Agricultural and Food Science in Finland 347 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. © Agricultural and Food Science in Finland Manuscript received April 2001 Weeds in spring cereal fields in Finland – a third survey Jukka Salonen, Terho Hyvönen and Heikki Jalli MTT Agrifood Research Finland, Plant Production Research, FIN-31600 Jokioinen, Finland, e-mail: jukka.salonen@mtt.fi A survey of weeds in spring cereal fields was conducted in 16 regions of southern and central Finland in 1997–1999. Data were collected from conventional and organic farms, both of which applied their normal cropping practices. A total of 690 fields were investigated by counting and weighing the weed species from ten sample quadrats 0.1 m2 in size in late July – early August. Altogether 160 weed species were found, of which 134 were broad-leaved and 26 grass species. The total number of weed species ranged from 41 to 84 between regions. In organically farmed fields, the average species number was 24 and in conventionally farmed fields 16. The most frequent weed species were Viola arvensis 84%, Stellaria media 76% and Galeopsis spp. 70%. Only 18 species exceeded the frequency level of 33%. The average density of weeds was 136 m–2 (median= 91) in sprayed conventional fields, 420 m–2 (374) in unsprayed conventional fields and 469 m–2 (395) in organic fields. The average air- dry above-ground biomass of weeds was 163 kg ha–1 (median=63), 605 kg ha–1 (413) and 678 kg ha–1 (567), respectively. Weed biomass accounted for 3% of the total biomass of the crop stand in sprayed conventional fields and for 17% in organic fields. Elymus repens, the most frequent grass species, produced the highest proportion of weed biomass. Key words: weeds, cereals, biodiversity, organic farming, crop protection Introduction MTT Agrifood Research Finland has carried out two extensive surveys of weeds in spring cereal fields in Finland, the first in 1961–1964 (Muku- la et al. 1969) and the second in 1982–1984 (Erviö and Salonen 1987). Similar surveys have been conducted elsewhere, e.g. in England (Chancellor and Froud-Williams 1984), Den- mark (Andreasen et al. 1991), Germany (Al- brecht 1995) and Hungary (Tóth et al. 1999). Regular weed surveys are considered a nec- essary and valuable way of monitoring the re- sponses of weed floras to changes in agricultur- al practices and habitats. The most frequent and abundant weed species are of interest in terms of control measures. Current research projects focus not only on agricultural features of weed occurrence but also on biodiversity in agricul- mailto:jukka.salonen@mtt.fi 348 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salonen, J. et al. Weeds in spring cereals in Finland tural environments (Becker and Hurle 1998, Hald 1999). In the 1990s, crop production in Finland un- derwent changes that apparently affected weed floras in fields. The most marked changes were 1) the implementation of an extensive fallow scheme in the early 1990s, which peaked in 1994 at 505 000 ha (almost 25% of the cultivated area), 2) the switch to organic farming by roughly 5000 farms, accounting now for 6% of the cultivated field area and 3) the shift from the use of phe- noxy acid herbicides to sulphonylureas, which differ from the former in selectivity among weed species. Since 1995, when Finland became a member of the European Union, the economic basis of crop production has had to contend with cuts in prices of products. To compensate for losses to farmers, the government introduced a system of area-based subsidies taking into account certain special conditions. The Agri-Environmental Sup- port Scheme was launched with the aim, among others, of promoting the environmentally sus- tainable use of fertilizers and pesticides (Minis- try of Agriculture and Forestry 1999). A longer term change in agriculture has been the regional specialization of production. Now- adays, southern and south-western Finland are characterized by a high dominance of cereal crops in rotation whereas in central and eastern Finland the use of arable land is more diverse, many farms practising crop rotation based on grassland for silage and hay and pasture for cat- tle. Since this diversity of crop rotation has been found to have some effect on the species com- position (Bàrberi et al. 1997) and species diver- sity (Doucet et al. 1999) of weed communities, we expected to find differences between regions. The objective of the survey was to investi- gate the current status of weed occurrence in spring cereal fields, examining both convention- ally and organically cultivated fields. This first report focuses on the botanical composition of fields. It is aimed, on the one hand, at farmers, advisory services and the chemical industry with a view to promoting specific weed control meas- ures and, on the other, at scientists and authori- ties as a report on the diversity of weed flora. A more detailed analysis of the factors explaining weed occurrence and changes in weed floras over the decades will be given separately. Material and methods Study regions, farms and fields The present weed survey was carried out in southern and central Finland in 1997–1999. The 16 regions surveyed (Fig. 1, Table 1) are referred to in tables and figures by the numbers given in Table 1. Regions 1 and 2 were studied in 1997 as a preliminary survey. The other regions (nos. 3–16) were chosen from those studied in surveys conducted in the 1960s and 1980s. The initial intention of this survey was to visit exactly the same fields as those studied earlier but this was not entirely practicable, since spring cereals were Fig. 1. Weed survey regions in 1997–1999. Key to region numbers: 1 = Jokioinen, 2 = Lammi, 3 = Nauvo/Korppoo, 4 = Tammela, 5 = Laukaa/Toivakka, 6 = Kitee, 7 = Mikke- li, 8 = Paimio/Tarvasjoki, 9 = Laihia, 10 = Nivala, 11 = Laitila, 12 = Nurmijärvi, 13 = Vieremä, 14 = Kihniö/Par- kano, 15 = Iitti, 16 = Imatra/Ruokolahti. 349 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. not grown in many of the study fields in the par- ticular study year. The choice of study regions reflects the prev- alence of spring cereal crops in rotation in dif- ferent regions. Consequently, the highest number of fields was studied in south-western Finland, where spring cereals are grown in more than 50% of the arable area and annual spring-sown crops are predominant. The number of study fields decreased towards the east and north, where spring cereals account for less than 50% of the cultivated area, and many farms include grass- land in their crop rotation. The number of farms visited was 305, of which 229 engaged in conventional and 76 in organic farming. The study farms were either crop husbandry farms (174) without grassland in crop rotation or animal husbandry farms (131) with pasture in crop rotation. The fields of crop husbandry farms exceeded 70% of the studied fields in five regions (Nauvo/Korppoo, Paimio/ Tarvasjoki, Laihia, Nurmijärvi and Iitti) and those of animal husbandry farms in four regions (Jokioinen, Kitee, Nivala, Vieremä). The farm types were not evenly distributed over the study regions but reflected, as said, regional differenc- es in farming structure. The survey region in the south-western archipelago, Nauvo/Korppoo (3), was the only one without organically cultivated spring cereal fields. The proportion of organic Table 1. Number of fields surveyed by region, production type and cereal species. Number of fields Region Production type Cereal species Year No Total Conventional5 Organic Barley Oat Wheat Others Municipality 1997 Jokioinen1 01 62 47 (43) 15 41 15 05 01 Lammi2 02 63 44 (42) 19 21 29 08 05 1998 Nauvo/Korppoo 03 40 40 (36) 00 19 13 08 00 Tammela 04 53 44 (32) 09 34 13 04 02 Laukaa/Toivakka 05 46 34 (26) 12 20 26 00 00 Kitee 06 24 15 (10) 09 06 17 01 00 Mikkeli3 07 42 26 (26) 16 20 17 00 05 Paimio/Tarvasjoki4 08 73 57 (43) 16 22 06 45 00 1999 Laihia 09 42 37 (37) 05 27 11 04 00 Nivala 10 31 21 (16) 10 20 11 00 00 Laitila 11 51 38 (38) 13 34 14 03 00 Nurmijärvi 12 43 35 (35) 08 24 05 14 00 Vieremä 13 26 17 (12) 09 18 06 00 02 Kihniö/Parkano 14 33 24 (16) 09 09 23 01 00 Iitti 15 35 27 (26) 08 18 13 03 01 Imatra/Ruokolahti 16 26 19 (19) 07 10 14 01 01 Total 6900 525 (457) 1650 3430 2330 97 17 1 incl. Humppila, Jokioinen, Koski Tl, Loimaa municipality, Somero, Ypäjä 2 incl. Hämeenkoski, Kärkölä, Lammi, Mäntsälä, Pukkila 3 incl. Joroinen, Juva, Mikkeli, Mikkeli rural municipality 4 incl. Lieto 5 number of sprayed fields in parentheses 350 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salonen, J. et al. Weeds in spring cereals in Finland survey fields was highest, 30–38%, in Lammi, Kitee, Mikkeli, Nivala and Vieremä. Typically, a great majority of study fields were sown in mid-May (weeks no. 19–21) and sprayed with herbicides in mid-June (weeks no. 23–25). Weather conditions varied considerably between study years and regions (Table 2). On each farm, one to eight spring cereal fields were examined, giving a total of 690 fields: 343 under barley (Hordeum vulgare L.), 233 under oats (Avena sativa L.), 97 under wheat (Triticum aestivum L.) and 17 in mixed cultivation. Alto- gether 525 study fields were cultivated conven- tionally and 165 organically. To gain an overview of actual weed popula- tions in the middle of the growing season, no instructions on crop management, e.g. on herbi- cide use or fertilization, were given to farmers in advance. At the sampling time, the informa- tion on cropping measures was recorded by in- terviewing the farmers. The national regulation on organic cereal production bans the applica- tion of chemical fertilizers and pesticides and sets an upper limit on the use of organic fertiliz- ers (Ministry of Agriculture and Forestry 1999). The average area of the 690 study fields was 4.3 ha (range 0.2 ha – 35.3 ha), distributed in different size classes as follows: < 1 ha 065 fields 1–2 ha 151 fields 2–5 ha 257 fields 5–10 ha 148 fields > 10 ha 069 fields Herbicides had been applied in 457 out of 525, i.e. 87%, conventionally cultivated fields. Four major types of active ingredients had been used: pure MCPA (4-chloro-2-methylphenoxy- acetic acid) in 23% of treated fields, MCPA + other phenoxy acids (20%), sulphonylureas Table 2. Weather conditions in survey regions. Survey region Monthly precipitation ETS1 Year Region mm DD5 Municipality No May June July Total by 31-July Weather station 1997 Jokioinen 01 15 1010 1410 257 819 Jokioinen Lammi 02 12 73 1200 205 764 Lammi 1998 Nauvo/Korppoo 03 42 62 41 145 671 Korppoo Tammela 04 65 99 70 234 762 Jokioinen Laukaa/Toivakka 05 26 96 1120 234 688 Jyväskylä Kitee 06 53 1010 1460 300 712 Joensuu Mikkeli 07 32 83 1120 227 738 Mikkeli rural municipality Paimio/Tarvasjoki 08 27 93 72 192 817 Turku 1999 Laihia 09 21 36 35 092 822 Ylistaro Nivala 10 49 39 92 180 806 Nivala Laitila 11 06 30 16 051 918 Mietoinen Nurmijärvi 12 19 34 20 073 901 Vihti, Maasoja Vieremä 13 47 28 75 150 785 Kajaani Kihniö/Parkano 14 31 17 98 146 786 Ähtäri Iitti 15 17 52 49 118 943 Utti Imatra/Ruokolahti 16 06 30 35 071 10300 Lappeenranta (Source: Finnish Meteorological Institute) 1 ETS = Effective temperature sum in degree days accumulated above a base temperature of 5°C (DD5) 351 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. (42%) and phenoxy acids + sulphonylureas (15%). Weed sampling The present survey was carried out in 1997–1999 during a 4-week period starting in mid-July (weeks no. 28/29), by which time the spring ce- reals had reached their heading stage and at least 1 month had elapsed since herbicide treatment. The occurrence of weeds was assessed from 10 sample quadrats randomly placed in each field. For this purpose, each field was split in a 10 × 10 cell grid in which the positions of sam- ple quadrats were set with a random number cal- culator. The size of grid cells varied between fields according to the area of each field. Two sample quadrats were placed at a distance of 1– 3 m from the sown field edge and the other eight more than 5 m from the edge. Weed density was determined by counting the number of plants or shoots of grass weeds by species in a rectangular frame measuring 0.1 m2 (25 cm × 40 cm), which was a corner area with- in a larger quadrat measuring 1.0 m2 (1.0 m × 1.0 m). The larger quadrat was used for obser- vations of the presence/absence of each species. In 1997 (Jokioinen and Lammi), only the 0.1 m2 sample quadrats were used in the sampling. The results presented in the tables and figures derive from data collected from the 0.1 m2 quadrats and pooled over the samples in each field. A com- plete list of the additional weed species found in the presence/absence observation is given in Appendix 1 as a supplement to the 42 species presented in the tables. In four out of ten small sample quadrats, weeds and cereals were cut at the soil surface and their biomass was weighed by species after the samples had been dried in an air-flow dryer at 40°C for some days. The average biomass of a single plant was calculated by dividing the biomass of each species by the numbers of that plant in fields where the species was present, pro- vided that data were available from at least 20 fields. Nomenclature and data analysis As the present survey focused on the diversity of weed flora, all weed species found in sam- pling areas were assessed. Nevertheless, some genera/taxa, e.g. Galeopsis spp. and Lamium spp., had to be pooled since they could not be identified by species at the small seedling stage. The plant species nomenclature follows Hämet-Ahti et al. (1998), and the BAYER codes of weeds were derived from the BAYER AG company (Bayer 1992). The most recent change in nomenclature concerns Polygonum species, as they are now divided into four families: Aco- nogonon, Bistorta, Persicaria and Polygo- num (Hämet-Ahti et al. 1998). Consequently, Bistorta vivipara (L.) Gray (alias Polygonum viviparum L.), Persicaria hydropiper (L.) Spach (alias Polygonum hydropiper L.), Persicaria la- pathifolia (L.) Gray (alias Polygonum lapathi- folium L.) and Persicaria maculosa Gray (alias Polygonum persicaria L.) have been re-named. The full scientific names with attribution are given in Table 3. The term frequency indicates the proportion of fields where the species was found. The fre- quency results are classified as in Mukula et al. (1969). For each field, the total weed density and biomass were summed, and the averages, stand- ard deviations and median values are given in the text. To ensure consistency with the manner of data presentation in previous surveys (Muku- la et al. 1969, Erviö and Salonen 1987), the av- erage weed densities and dry weights by species are presented. Median values are given for total biomass and density but not for single species since most of the median values would have been zero due to the low frequency. The results of the three surveys should none- theless be compared with caution as the sampling technique used in the present survey was slight- ly modified in terms of size and number of quad- rats. Furthermore, in contrast to previous sur- veys, the majority, 66%, of the fields studied were sprayed with herbicides. The similarity of species composition be- tween regions was compared by Jaccard’s simi- 352 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salonen, J. et al. Weeds in spring cereals in Finland Table 3. Frequencies (%) of weed species by region. Year / Region Species / Taxon 1997 1998 1999 Average 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1997–99 Achillea millefolium L. 3 5 0 8 7 21 10 0 0 3 2 5 12 15 9 4 5 Brassica rapa L. ssp. oleifera (DC.) METZG. 15 14 0 2 11 0 5 3 12 0 20 14 0 27 9 4 9 Capsella bursa-pastoris (L.) MEDIK. 15 24 8 28 39 58 45 16 7 10 18 5 31 39 14 12 22 Cerastium fontanum BAUMG. 0 3 0 13 22 46 21 4 2 19 0 0 46 12 0 4 10 Chenopodium album L. 77 83 65 60 80 83 52 56 50 77 80 63 65 79 63 39 68 Cirsium arvense (L.) SCOP. 29 22 18 38 17 8 17 33 14 13 4 33 19 12 29 31 22 Elymus repens (L.) GOULD 63 73 60 68 76 96 81 43 62 74 61 47 65 70 77 81 66 Epilobium angustifolium L. 2 0 0 11 9 8 7 14 0 7 2 0 15 18 0 12 6 Equisetum arvense L. 18 14 20 21 20 8 21 40 5 6 12 12 35 15 3 8 17 Erysimum cheiranthoides L. 36 48 55 55 63 71 57 43 26 55 33 21 73 64 37 42 47 Fallopia convolvulus (L.) À. LÖVE 50 54 35 66 22 46 38 69 71 48 65 61 8 24 66 85 52 Fumaria officinalis L. 32 56 25 36 61 46 24 45 17 16 27 74 23 33 51 69 40 Galeopsis L. spp. 79 87 38 68 91 79 57 77 60 94 61 40 89 88 54 62 70 Galium spurium L.a 37 38 83 64 20 29 19 53 55 7 53 47 19 0 49 42 41 Gnaphalium uliginosum L. 7 29 0 47 83 71 57 23 0 84 8 2 92 70 11 46 34 Juncus bufonius L. 0 2 0 15 26 38 36 0 0 19 0 0 12 15 0 4 9 Lamium L. spp. 32 25 78 28 15 8 14 60 12 0 43 35 0 9 26 39 30 Lapsana communis L. 47 79 80 68 74 54 81 36 7 0 69 35 0 15 66 89 52 Lathyrus pratensis L. 18 5 0 8 0 0 2 8 5 3 0 2 8 0 6 8 5 Matricaria matricarioides (LESS.) PORT. 26 25 8 45 85 63 57 29 17 61 20 0 65 58 31 42 37 Myosotis arvensis (L.) HILL 37 46 23 51 72 58 91 67 31 23 22 7 54 52 37 54 46 Persicaria hydropiper (L.) SPACH 0 0 0 23 11 29 31 0 0 3 18 0 0 9 17 42 10 Persicaria lapathifolia (L.) GRAY 40 59 15 45 54 46 36 37 29 74 20 2 85 88 20 62 42 Persicaria maculosa GRAY 0 0 0 11 0 0 0 34 0 0 22 21 0 0 17 23 9 Plantago major L. 8 14 10 21 50 75 50 7 2 26 8 0 89 21 11 27 22 Poa annua L. 7 3 0 23 7 33 41 7 5 3 24 5 8 6 9 27 12 Polygonum aviculare L. 55 73 18 59 52 71 41 44 43 81 75 67 73 73 71 42 58 Ranunculus acris L. 7 16 0 11 54 4 10 6 0 10 2 0 50 55 0 0 13 Ranunculus repens L. 0 25 8 13 37 67 36 10 2 55 6 5 62 9 6 27 19 Rumex acetosa L. 0 5 0 0 30 0 5 1 0 7 2 0 12 36 0 4 6 Rumex acetosella L. 3 8 0 15 11 25 12 3 5 10 0 0 15 0 0 4 6 Sonchus arvensis L. 36 71 23 47 70 25 41 25 17 26 20 19 42 36 46 58 38 Spergula arvensis L. 39 64 33 62 87 71 71 34 21 65 35 21 77 82 40 50 51 Stellaria media (L.) VILL. 87 86 58 85 78 100 67 89 64 90 67 35 69 85 57 85 76 Taraxacum officinale WEBER in WIGGERS 45 8 3 45 13 71 12 51 0 7 0 7 54 18 6 54 24 Thlaspi arvense L. 15 25 3 8 9 4 2 11 7 19 8 2 0 12 20 12 10 Trifolium L. spp. 26 57 28 36 41 67 33 32 19 35 14 14 77 45 31 27 35 Tripleurospermum inodorum (L.) SCH. BIP. 53 41 45 55 43 13 45 71 14 52 10 28 31 24 34 31 40 Tussilago farfara L. 2 10 3 23 20 8 19 11 0 7 6 0 23 12 6 12 10 Veronica serpyllifolia L. 0 0 0 13 13 17 5 6 0 10 0 0 73 15 0 12 8 Vicia cracca L. 16 16 3 15 0 13 14 8 7 10 16 14 23 18 9 4 12 Viola arvensis MURRAYb 81 91 93 87 94 92 100 89 83 65 80 56 85 82 71 96 84 a = incl. G. aparine, b = incl. V. tricolor 353 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. larity coefficient Sj (Jaccard 1912) (Sj = c/(A + B – c), where c = number of species common to both samples A and B, A = number of species in sample A, B = number of species in sample B). The data were pooled over all fields of each re- gion before the analysis. The results of similari- ties were presented as dendrograms in which average-linkage clustering (the unweighted pair- group method) was applied (see Krebs 1999). The diversity of weed species was described by species richness and evenness. The number of species was used as a measure of species rich- ness. Since the number of species depends on the sample size and since the number of sam- pled fields varied between regions, total species numbers between regions could not be compared. Therefore, the expected number of species E(Sn) was calculated for each region by rarefaction: where E(Sn) = expected number of species in a random sample of n individuals, S = total number of species in the entire collection, Ni = number of individuals in species i, N = total number of individuals in the collection, n = sample size (number of individuals) chosen for standardiza- tion (see Heck et al. 1975, Krebs 1995). In rarefaction, the number of species of larg- er samples are scaled down to the given number of individuals which permits the comparison of species numbers between samples differing in size. Since the lowest number of individuals observed was 3386, we scaled sample sizes down to 3300 individuals in the data sets of all fields. In conventional sprayed and organic fields the lowest numbers of individuals were 1519 and 1867, respectively, and we scaled the number of individuals down to 1500. In all data sets, the lowest number of individuals was in the Nurmi- järvi region. The sample size of 1500 individu- als was used in both data sets to permit the com- parison of numbers of species between conven- tional sprayed and organic fields. Hill’s even- ness index E2,1 where pi is the proportion of the total sample be- longing to the ith species (for properties of the index, see Alatalo 1981) was used as a measure of evenness. Species richness and evenness were calculated for each field separately. Data from the ten 0.1 m2 sample quadrats were pooled be- fore the calculation. The evenness index was calculated by using data on the number of indi- viduals. Results Frequency of weed species The occurrence of the 42 most frequent weed species that exceeded the overall frequency lev- el of 5% in the small sample quadrats is present- ed by region (Tables 3, 8–9); the remaining spe- cies observed from the larger quadrats are listed by region (Appendix 1). The five most common weed species were Viola arvensis, Stellaria media, Galeopsis spp., Chenopodium album and Elymus repens. These species occurred in more than 60% of the fields studied (Table 3). In contrast, most of the ob- served 160 weed species were fairly rare as they were found in less than 2% of the survey fields (Table 4 and Table 5). With a frequency of 66%, Elymus repens was by far the most common grass weed (Table 3). The next most common grass species, although much lower in the ranking list, were Poa annua (frequency 12%), Phleum pratense (3%) and Alopecurus geniculatus (3%). With the excep- tion of E. repens and P. annua, however, the grass species could not always be identified by spe- cies at seedling stage. Thus, they were only re- corded and pooled to a monocot class that reached a frequency level of 26%. The ranking list of the ten most frequent weed species in the conventional fields sprayed with 354 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salonen, J. et al. Weeds in spring cereals in Finland herbicides was somewhat different from that in the organic fields (Table 6). Highly productive perennial weeds occurred more frequently in organic than in conventional farming; Elymus repens had a frequency of 81% in organic and 60% in conventional farming, Sonchus arvensis 54% and 31% and Cirsium arvense 34% and 15%, respectively. Similarly, typical grassland weed species such as Achillea millefolium 15% vs. 2%, Ranunculus repens 30% vs. 12% and Taraxacum officinale 30% vs. 20% were more frequent in organic than in conventional farm- ing. The most common weed species were found every year and in all regions, although their rank order varied between the regions. In contrast, some species, e.g. Lamium spp. in south-west- ern Finland, Gnaphalium uliginosum in central Finland and Veronica serpyllifolia in the Vieremä region, were common only in some regions. The analysis of species composition with similarity indices revealed two main groups of which the first consisted of two subgroups (Fig. 2), one in south-western (Jokioinen, Laitila and Paimio/Tarvasjoki) and one in southern Finland (Lammi, Iitti, Imatra/Ruokolahti and Nurmijärvi) and the Laihia region in Ostrobothnia. The sec- ond main group included regions (Tammela, Mikkeli, Laukaa/Toivakka, Vieremä, Kihniö/ Parkano, Kitee and Nivala) throughout Finland. The most striking difference in species compo- sition between the two main groups was the ab- sence of many species (Cerastium fontanum, Juncus bufonius, Veronica serpyllifolia, Ranun- culus acris and Epilobium angustifolium) from some regions of the first group whereas in the Table 4. Distribution of annual and perennial weed species into frequency classes. Frequency Life history % Annuals % Perennials % Total % 00–2 34 50 64 70 98 61 03–4 04 06 06 07 10 06 05–8 01 01 10 11 11 07 09–16 09 13 04 04 13 08 17–32 04 06 06 07 10 06 33–64 13 19 01 01 14 09 65– 03 04 01 01 04 03 Total 68 92 1600 Table 5. Distribution of broad-leaved and grass weed species into frequency classes. Frequency Growth form % Broad-leaved % Grass % Total % 00–2 78 58 20 77 98 61 03–4 07 05 03 12 10 06 05–8 11 08 00 00 11 07 09–16 12 09 01 04 13 08 17–32 09 07 01 04 10 06 33–64 14 10 00 00 14 09 65– 03 02 01 04 04 03 Total 1340 26 1600 355 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. second group they were found in all regions (Ta- ble 3). The species composition in the Nauvo/ Korppoo region (no organic farming) differed most markedly from that in any of the other re- gions because some species, e.g. Gnaphalium uliginosum, Persicaria hydropiper and Poa an- nua, were not found there at all (Table 3). Species diversity Altogether 188 weed species were found in the large (1.0 m2) sampling quadrats and 160 in the small (0.1 m2) quadrats. The total number of observed species, SOBS, in regions ranged from 41 to 84 (Table 7). In three regions (Nauvo/Korp- poo, Laihia and Nurmijärvi), the number of ob- served species was below 50 and in two regions (Tammela and Mikkeli) it exceeded 80. The same regions had the lowest and the highest expected number of species, E(Sn), calculated by rarefac- tion analysis (Table 7). No clear regional trend in the variation in the total number of species was observed. For example, the regions with the highest species number included regions in both eastern (Kitee, Mikkeli and Imatra/Ruokolahti) and south-western (Tammela and Paimio/Tarvas- joki) Finland. In 11 out of 15 regions, the total number of observed species, SOBS, was higher in organical- ly farmed than in sprayed conventional fields, whereas the expected number of species, E(Sn), was higher in organically farmed fields in nine regions (Table 7). However, even though the number of species might be almost the same, the species composition could be very different. For example, in the Imatra/Ruokolahti region the difference in the number of observed species, SOBS, was only two but the proportion of co-oc- curring species was as low as 54.9% (Table 7). Table 6. Frequency of ten most common weed species in two cropping systems. Rank Sprayed conventional (N = 457) % Organic (N = 165) % 01 Viola arvensis 81 Chenopodium album 96 02 Stellaria media 65 Stellaria media 95 03 Elymus repens 60 Galeopsis spp. 93 04 Galeopsis spp. 60 Viola arvensis 93 05 Chenopodium album 53 Spergula arvensis 83 06 Lapsana communis 52 Erysimum cheiranthoides 82 07 Polygonum aviculare 50 Elymus repens 81 08 Fallopia convolvulus 48 Polygonum aviculare 70 09 Galium spurium 43 Fallopia convolvulus 63 10 Fumaria officinalis 39 Myosotis arvensis 60 Fig. 2. Similarity (Jaccard’s similarity coefficient) of weed communities between regions. Key to region numbers: 1 = Jokioinen, 2 = Lammi, 3 = Nauvo/Korppoo, 4 = Tammela, 5 = Laukaa/Toivakka, 6 = Kitee, 7 = Mikkeli, 8 = Paimio/ Tarvasjoki, 9 = Laihia, 10 = Nivala, 11 = Laitila, 12 = Nur- mijärvi, 13 = Vieremä, 14 = Kihniö/Parkano, 15 = Iitti, 16 = Imatra/Ruokolahti. Ja cc a rd ’s s im ila ri ty c o e ff ic ie n t 356 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salonen, J. et al. Weeds in spring cereals in Finland The average number of weed species per field was 18. In organically farmed fields, the average species number was 24 and in conventionally farmed fields 16. However, in conventional fields the difference between sprayed and unsprayed fields was ten species (15 vs. 25 species). The difference in the average number of weed spe- cies between the poorest and the richest regions was 11 in both sprayed conventional and organ- ic fields (Fig. 3). The number of species was, however, higher in organic fields (variation in averages 14–25.1) than in sprayed conventional fields (6.6–17.6). The greater the number of spe- cies in sprayed conventional fields, the lower were the values of the evenness index (i.e. some species dominated the weed community); a sim- ilar trend was not observed in organic fields. Weed density The average density of weeds in all fields studied was 243 plants m–2 (SD = 261, median = 160, N = 690). Correspondingly, the average density of weeds in sprayed conventional fields was 136 plants m–2 (SD = 136, median = 91, N = 457) and in organic production 469 plants m–2 (SD = 340, median = 395, N = 165). The average weed density in untreated conventional fields was 420 plants m–2 (SD = 238, median = 374, N = 68). The three most abundant weed species ac- counted for 32–53% of the total density in each region. There were considerable differences in the abundance of weeds between the regions (Table 8), reflecting both annually changing fac- tors such as weed control measures and weather conditions and more permanent factors such as soil conditions and farming practices. Some less frequent species, e.g. Juncus bufonius, Persi- caria hydropiper and Veronica serpyllifolia, were of importance in some regions. The five most abundant weed species in or- ganic fields were Chenopodium album (on aver- age 91 plants m–2), Elymus repens (49), Spergu- la arvensis (49), Stellaria media (49) and Viola arvensis (31). Correspondingly, the five most abundant weed species in sprayed conventional fields were Elymus repens (21 plants m–2), Viola arvensis (15), Stellaria media (12), Chenopo- dium album (8), and Spergula arvensis (7). Table 7. Observed (S OBS ) and rarefied (E(S n ) with SD) number of species by region and production type, and proportion of co-occurring species between sprayed conventional and organic fields. Region All fields Conventional sprayed Organic Co-occurring S OBS E(S 3300 ) SD S OBS E(S 1500 ) SD S OBS E(S 1500 ) SD species (%) 01 Jokioinen 54 51.8 1.24 41 38.0 1.27 47 41.5 1.63 66.7 02 Lammi 62 53.2 2.04 48 39.8 2.01 57 44.7 2.19 72.6 03 Nauvo/Korppoo 41 38.1 1.41 39 34.0 1.62 – – – – 04 Tammela 84 64.6 2.64 65 51.3 2.35 55 48.2 2.00 57.1 05 Laukaa/Toivakka 68 57.1 2.13 48 40.2 1.76 53 46.1 2.03 64.7 06 Kitee 72 62.5 2.11 47 43.3 1.54 60 52.2 1.92 59.7 07 Mikkeli 81 69.5 2.41 66 56.7 2.24 64 50.1 2.47 60.5 08 Paimio/Tarvasjoki 72 56.9 2.40 46 40.5 1.77 55 42.0 2.30 54.2 09 Laihia 42 41.2 0.81 40 38.0 1.23 26 25.2 0.81 57.1 10 Nivala 56 44.8 2.21 42 37.1 1.71 47 33.8 2.12 64.3 11 Laitila 61 48.4 2.38 51 40.5 2.26 46 36.9 1.83 59.0 12 Nurmijärvi 44 43.9 0.36 33 32.9 0.27 40 38.7 1.03 65.9 13 Vieremä 66 55.4 2.36 47 45.3 1.20 49 40.4 1.90 68.2 14 Kihniö/Parkano 60 54.5 1.59 39 34.5 1.62 47 43.2 1.46 63.3 15 Iitti 55 51.0 1.63 43 35.0 1.99 46 36.5 1.98 67.3 16 Imatra/Ruokolahti 71 61.9 2.17 54 43.9 2.12 56 49.7 1.85 54.9 357 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. Weed biomass The average biomass production of weeds was 329 kg ha–1 (SD = 444, median = 141, N = 690) (Table 9). The difference between cropping prac- tices was considerable, as in sprayed convention- al fields the average weed biomass was 163 kg ha–1 (SD = 248, median = 63, N = 457) and in organic production it was about four times as high, namely 678 kg ha–1 (SD = 547, median = 567, N = 165). Moreover, in terms of median values, the difference in biomass production was 9-fold. In untreated conventional fields the aver- age weed biomass was 605 kg ha–1 (SD = 560, median = 413, N = 68). Although the average biomass production of weeds varied between the regions (Table 9), the annual averages pooled over the regions were at roughly the same level: 227 kg ha–1 in 1997, 251 kg ha–1 in 1998 and 244 kg ha–1 in 1999. In all regions, the three most abundant weed species together accounted for more than 50% of the average total biomass production in the region. The same species were quite often the most productive (e.g. Elymus repens, Chenopo- dium album) in different regions. Perennial Fig. 3. Number of species and values of evenness index (E 2,1 ) by region in sprayed conventional and organically cultivated fields. The square in the box denotes the mean of the data, and the horizontal lines the 25th, 50th and 75th percentile values. The error bars denote the 5th and 95th percentile values, and the crosses below and above them the 1st and the 99th percentile values, respectively. Key to region numbers: 1 = Jokioinen, 2 = Lammi, 3 = Nauvo/Korppoo, 4 = Tammela, 5 = Laukaa/Toivakka, 6 = Kitee, 7 = Mikkeli, 8 = Paimio/Tarvasjoki, 9 = Laihia, 10 = Nivala, 11 = Laitila, 12 = Nurmijärvi, 13 = Vieremä, 14 = Kihniö/Parkano, 15 = Iitti, 16 = Imatra/Ruokolahti. 358 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salonen, J. et al. Weeds in spring cereals in Finland Table 8. Weed density (plants m–2) by region. + indicates <1 plant m–2. Year / Region Species / Taxon 1997 1998 1999 Average 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1997–99 Achillea millefolium + + 0 + + + + 0 0 + + + + + + + + Brassica rapa ssp. oleifera + + 0 + + 0 + + 2 0 1 + 0 + + + + Capsella bursa-pastoris + 2 1 3 2 8 6 + + + 1 + + 2 2 + 2 Cerastium fontanum 0 + 0 + + 5 + + + + 0 0 1 2 0 + + Chenopodium album 22 63 17 21 13 28 24 18 23 73 48 24 32 39 83 16 33 Cirsium arvense 1 + + + + + + 1 + + + 1 + + 1 + + Elymus repens 28 23 11 33 32 73 49 9 6 45 18 11 22 37 58 81 29 Epilobium angustifolium + 0 0 + + + + + 0 + + 0 + 1 0 + + Equisetum arvense 1 + 1 1 + + + 3 + + + + + 1 + + + Erysimum cheiranthoides 3 5 3 3 8 7 10 5 9 10 2 + 3 10 12 3 6 Fallopia convolvulus 3 4 1 7 + 1 1 5 6 2 4 6 + + 9 21 4 Fumaria officinalis 2 3 2 2 7 2 + 2 + + 1 6 + 2 3 3 2 Galeopsis spp. 9 19 + 9 17 6 9 8 7 42 12 3 24 14 7 3 12 Galium spurium 4 9 14 5 + + + 4 3 + 5 2 + 0 7 10 4 Gnaphalium uliginosum + 6 0 11 31 28 11 1 0 29 + + 37 12 2 9 9 Juncus bufonius 0 + 0 4 3 1 8 0 0 2 0 0 + 1 0 + 1 Lamium spp. 5 2 10 2 4 + + 10 + 0 2 2 0 + 2 8 3 Lapsana communis 3 13 5 9 13 18 17 1 + 0 14 1 0 + 14 35 8 Lathyrus pratensis + + 0 + 0 0 + + + + 0 + + 0 + + + Matricaria matricarioides 5 2 2 3 31 16 10 4 + 25 1 0 18 23 6 10 8 Myosotis arvensis 1 3 + 9 7 4 12 8 1 3 3 + 2 3 3 5 4 Persicaria hydropiper 0 0 0 2 3 1 2 0 0 + 3 0 0 + + 2 + Persicaria lapathifolia 11 13 4 4 9 3 3 2 1 27 3 + 18 9 + 2 7 Persicaria maculosa 0 0 0 + 0 0 0 5 0 0 + + 0 0 + + + Plantago major + + + 1 8 13 5 + + 3 + 0 15 + 1 3 2 Poa annua + + 0 5 2 9 16 + + + 3 + 2 + + 8 3 Polygonum aviculare 2 2 1 4 2 5 + 2 1 5 9 7 12 6 6 4 4 Ranunculus acris + + 0 + 2 + + + 0 + + 0 1 13 0 0 + Ranunculus repens 0 1 + + 3 6 1 + + 12 + + 8 3 + + 2 Rumex acetosa 0 + 0 0 1 0 + + 0 + + 0 + 2 0 + + Rumex acetosella 1 + 0 + + + + + + + 0 0 + 0 0 + + Sonchus arvensis 1 7 1 6 14 1 7 1 + 3 4 + 3 2 4 8 4 Spergula arvensis 19 20 8 19 52 28 25 5 1 46 9 2 36 41 18 10 20 Stellaria media 24 28 10 48 32 22 17 32 8 62 25 3 17 19 14 25 25 Taraxacum officinale 2 + + 1 + 6 + 4 0 + 0 + 3 1 + 3 1 Thlaspi arvense + 1 + + + + + + + 1 + + 0 1 10 2 1 Trifolium spp. + 6 + 2 3 5 3 + + 2 2 + 6 4 10 + 3 Tripleurospermum inodorum 3 5 1 2 6 3 2 16 + 5 2 + 3 2 4 + 4 Tussilago farfara + + + 2 2 1 3 + 0 + + 0 + + + 1 + Veronica serpyllifolia 0 0 0 + 2 + + + 0 + 0 0 6 3 0 + + Vicia cracca + + + 1 0 + + + + + + + + + + + + Viola arvensis 12 29 30 14 16 20 30 19 15 25 23 6 12 13 17 28 19 Other broad-leaved 4 5 2 6 9 18 6 13 + 7 3 1 10 14 11 8 7 Other grasses + 6 1 3 28 7 16 10 6 28 3 + 39 41 6 3 11 Mean total, plants m–2 173 280 129 245 365 350 302 187 96 459 202 79 330 322 303 314 243 Median total, plants m–2 108 208 88 188 290 270 249 129 52 299 105 41 298 255 134 305 160 359 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. weeds such as Cirsium arvense, Sonchus arven- sis and Tussilago farfara also ranked high, since one individual perennial plant alone may pro- duce more biomass than 100 seedlings of annual broad-leaved weeds. The five weed species producing the highest amounts of biomass in organic fields were Ely- mus repens (average 178 kg/ha), Chenopodium album (140), Spergula arvensis (53), Galeopsis spp. (47) and Stellaria media (37). Correspond- ingly, the five most productive weed species in sprayed conventional fields were Elymus repens (81 kg ha–1), Chenopodium album (10), Stella- ria media (7), Galeopsis spp. (7), and Persicaria lapathifolia (6). The average biomasses of individual weed plants and their rank order differed in sprayed conventional and organic cropping as indicated in the list of the 15 most productive species (Ta- ble 10). Eleven of these were the same species in both cropping types. Broad-leaved species accounted for 43% of the average total biomass production in sprayed conventional fields and for 72% in organic fields. Elymus repens was the most efficient biomass producer, as it accounted for 26% of the total weed biomass production pooled over all organ- ic fields and for as much as 50% in sprayed con- ventional fields. In all, the proportion of weed biomass rela- tive to total vegetative biomass (crop + weeds) was fairly low (mean = 3.0%) in sprayed con- ventional fields, somewhat higher (mean = 12.6%) in untreated conventional fields and highest (mean = 17.1%) in organic fields. Discussion Species diversity in cereal fields was fairly high, a total of 160 weed species, actually 188 spe- cies, being found in the surveyed fields. The clas- sification of species into broad-leaved/grass and annual/perennial types showed a similar distri- bution over the frequency classes. Characteris- tic of weed infestation in spring cereal fields is the occurrence of broad-leaved annuals and Ely- mus repens. Only 42 weed species/taxa exceeded the overall frequency level of 5%. Furthermore, al- though the number of weed species observed was fairly high, the number of dominant weed spe- cies was quite low, as only 18 species exceeded the frequency level of 33% and more than 60% of the species remained below the 2% frequen- cy level. In terms of successful cereal produc- tion, shifts in the rank order of the most frequent and dominant species should have greater im- plications for the planning of weed management than have actual changes in the diversity of weed communities, as suggested also by Légère and Derksen (2000). The present finding of 160 (188) weed spe- cies along with the earlier finding of 304 spe- cies (Mukula et al. 1969) shows that spring ce- real fields support a much more diverse weed flora than which is important in terms of crop protection. Due to the difference in sample sizes, however, the findings of these two surveys can- not be directly compared. Further, we may ex- pect that some weed species detected previous- ly are now extinct or extremely rare in Finnish arable fields. Such a decline in arable flora has been observed in other countries, too (Albrecht 1995, Andreasen et al. 1996, Sutcliffe and Kay 2000). Regional specialization of agricultural prac- tices has taken place in many countries – includ- ing Finland – during the last decades. The study regions in southern and south-western Finland can be regarded as this country’s main cereal production area. In other study regions, the use of arable land is more diverse as many farms base their crop rotation on grassland for silage and hay and pasture for cattle. These two areas proved to have a different weed species compo- sition and species diversity. Regions in central and eastern Finland had, in general, higher av- erage weed species numbers than did regions in southern and south-western Finland. Species absent from southern and south-western Finland were those typical of Finnish grasslands (Raa- 360 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salonen, J. et al. Weeds in spring cereals in Finland Table 9. Average biomass (kg ha–1) of weeds by region. + indicates <1 kg ha–1. Year / Region Species / Taxon 1997 1998 1999 Average 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1997–99 Achillea millefolium 0 2 0 + + 2 + 0 0 0 0 + + 2 + 0 + Brassica rapa ssp. oleifera 4 2 0 + + 0 0 + 2 0 17 1 0 3 + 0 2 Capsella bursa-pastoris + + + + 1 3 5 + 0 0 + 0 + 3 + + + Cerastium fontanum 0 0 0 0 0 + + 0 0 0 0 0 + 1 0 0 + Chenopodium album 31 123 4 10 7 17 11 4 95 75 93 31 107 60 69 53 47 Cirsium arvense 11 3 9 31 0 0 + 32 2 + 0 9 7 + 7 8 9 Elymus repens 102 91 49 140 154 175 215 58 41 142 63 43 136 128 133 309 112 Epilobium angustifolium 0 0 0 0 + + + 0 0 0 0 0 + 3 0 + + Equisetum arvense 2 + 6 6 + 0 2 11 3 + 2 5 4 2 0 0 3 Erysimum cheiranthoides + 3 + 2 2 4 8 2 14 4 1 + 3 15 14 6 4 Fallopia convolvulus 6 9 + 8 + + 1 4 9 3 8 13 0 + 15 32 7 Fumaria officinalis 2 2 + 2 7 2 + 2 3 + 5 2 + 3 4 3 2 Galeopsis spp. 11 25 + 25 28 15 27 25 31 46 27 3 50 31 10 8 22 Galium spurium 2 8 9 7 + + 3 11 1 0 7 + 0 0 3 4 4 Gnaphalium uliginosum 0 + 0 2 3 + + 0 0 3 0 0 3 1 0 + + Juncus bufonius 0 + 0 4 + + 6 0 0 0 0 0 + + 0 0 + Lamium spp. 2 + 1 1 2 + 0 6 0 0 1 1 0 + + 3 1 Lapsana communis + 11 + 10 6 16 18 + + 0 10 + 0 + 5 33 6 Lathyrus pratensis + 0 0 3 0 0 0 + 0 0 0 0 + 0 0 + + Matricaria matricarioides + + + 1 16 5 3 2 0 6 + 0 15 9 2 4 3 Myosotis arvensis 0 1 + 3 2 1 6 1 + + + 0 + 1 + 1 1 Persicaria hydropiper 0 0 0 3 + 2 3 0 0 + + 0 0 + + 2 + Persicaria lapathifolia 9 37 5 8 14 3 5 3 4 77 4 0 28 13 + 14 13 Persicaria maculosa 0 0 0 + 0 0 0 1 0 0 + + 0 0 1 + + Plantago major 1 0 + + 3 2 7 + + + + 0 2 + + 2 1 Poa annua + + 0 3 + 1 3 + + 0 + + + + 0 1 + Polygonum aviculare 2 3 1 3 2 4 + + 2 6 9 10 34 7 4 7 5 Ranunculus acris 0 0 0 0 + 0 0 0 0 0 0 0 + 2 0 0 + Ranunculus repens 0 + 0 + 3 2 2 + 0 4 0 0 4 3 0 + + Rumex acetosa 0 0 0 0 + 0 0 0 0 + 0 0 + 1 0 0 + Rumex acetosella + 0 0 + + + + 0 + + 0 0 0 0 0 0 + Sonchus arvensis 5 19 1 31 27 + 30 + + 9 8 + 5 4 9 35 11 Spergula arvensis 2 14 8 23 44 17 36 5 3 50 26 + 56 65 9 7 20 Stellaria media 6 9 2 52 28 37 20 35 6 32 14 1 19 16 6 16 19 Taraxacum officinale 0 + 0 + + 9 + + 0 0 0 3 + + + 0 + Thlaspi arvense 0 + 0 + + 1 + 0 + + + 0 0 2 5 1 + Trifolium spp. + 5 0 + 2 + 2 + + + + + 6 1 8 + 2 Tripleurospermum inodorum + 1 + 2 6 + 2 3 + 2 1 + 4 1 1 2 2 Tussilago farfara 0 1 0 45 3 + 5 + 0 + 1 0 0 2 0 + 4 Veronica serpyllifolia 0 0 0 0 + 0 0 0 0 0 0 0 + + 0 0 0 Vicia cracca + 5 0 3 0 0 3 0 + + 1 + + 2 + 0 1 Viola arvensis 1 5 3 6 3 4 11 3 3 7 7 + 3 7 2 14 5 Other broad-leaved 2 4 1 6 2 9 4 3 + 3 6 2 + 4 11 25 5 Other grasses 0 6 + 7 35 5 31 4 5 7 2 + 48 16 3 6 10 Mean total, kg ha-1 204 389 103 448 402 342 468 216 225 478 319 129 537 408 317 599 329 Median total, kg ha-1 86 233 38 193 288 273 316 63 53 190 98 35 509 200 173 294 141 361 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. tikainen and Raatikainen 1975). Therefore, re- gional specialization in agricultural production can be regarded as one reason for differences in the composition of weed communities between these two areas. Another factor affecting the species compo- sition in different regions (probably in interac- tion with cropping practices) was soil proper- ties, organic soils being predominant in some regions of central and eastern Finland (e.g. Kitee and Nivala). Soil properties have been found to be an important factor explaining the species composition of weed communities (Andreasen et al. 1991). Salonen (1993) and Erviö et al. (1994) analysed the data of the second weed sur- vey and found that Chenopodium album, Lam- ium spp. and Fallopia convolvulus were more abundant in clay than in coarse mineral or or- ganic soils. Furthermore, Galeopsis spp. and Polygonum lapathifolium favoured organic soils and Poa annua and Lapsana communis coarse mineral soils. It should also be kept in mind that in both cereal and animal husbandry production systems the intensity of farming has increased tremen- dously and in many ways. The most striking changes during the last four decades have been the greater use of herbicides, increased nitrogen fertilization and improved tillage and sowing practices with combined seed and fertilizer drill methods (Elonen 1983, Mukula and Rantanen 1987). It is thus unlikely that any single factor alone can adequately explain the changes in weed flora (Haas and Streibig 1982, Salonen 1993). Another factor which should be taken into account when comparing regions is that the sur- veys were conducted in different years and un- der different weather conditions. Both 1997 and 1999 were fairly dry years, whereas 1998 was very wet. Surprisingly, however, the annual av- erages of weed biomass pooled over the regions were close to each other. Moreover, some regions were studied during the latter part of the one- month survey period; this obviously had some effect on the biomass results but not so much on the frequency and density records. Therefore, it was appropriate to use a qualitative similarity index, which treats all species equally, irrespec- tive of their abundance, in the comparison of species composition between regions although the rare species are assigned the same importance as the dominants. Both the average and median weed density and weed biomass were fairly high, particularly Table 10. The 15 most productive weed species (air-dry biomass, g/plant) in two cropping types. Sprayed conventional Organic Species g No of fields Species g No of fields Galeopsis speciosa 0.63 038 Cirsium arvense 2.39 056 Equisetum arvense 0.47 062 Brassica rapa ssp. oleifera 1.02 026 Elymus repens 0.44 273 Vicia cracca 0.41 041 Brassica rapa ssp. oleifera 0.25 028 Elymus repens 0.37 133 Tussilago farfara 0.24 024 Persicaria lapathifolia 0.35 087 Galeopsis bifida 0.24 092 Galeopsis speciosa 0.34 051 Cirsium arvense 0.24 070 Equisetum arvense 0.29 045 Persicaria lapathifolia 0.16 153 Galeopsis bifida 0.28 090 Fallopia convolvulus 0.15 219 Fallopia convolvulus 0.24 104 Taraxacum officinale 0.11 093 Sonchus arvensis 0.20 089 Sonchus arvensis 0.11 140 Lathyrus pratensis 0.18 020 Fumaria officinalis 0.10 180 Chenopodium album 0.17 159 Polygonum aviculare 0.10 228 Polygonum aviculare 0.16 115 Chenopodium album 0.10 241 Achillea millefolium 0.13 025 Lapsana communis 0.09 236 Spergula arvensis 0.12 137 362 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salonen, J. et al. Weeds in spring cereals in Finland in organic production and in the unsprayed fields of conventional production. In the early 1980s, the average weed density in unsprayed sample quadrats was 170 plants m–2 (median 124) and the average weed biomass 320 kg per hectare (median 183) (Salonen 1993). Furthermore, the biomass production of weeds in the 1960s aver- aged 1000 kg per hectare (Mukula 1974). The use of herbicides started to increase in cereal production in Finland in the early 1960s, the peak volume (kg active ingredients) being reached in the early 1980s (Hynninen and Blomqvist 1997). Since the 1990s, sulphonylu- reas have replaced phenoxyacid herbicides to such an extent that the current sprayed area of spring cereals is about the same for both herbi- cide types. Herbicide treatment in cereal produc- tion is still a common practice on conventional farms (Londesborough et al. 2000). Most of the survey farms used the lowest recommended ap- plication rate. The main reason for annual inter- ruptions to herbicide application was the unsuit- ability of weather conditions, either drought or an excess of rain. Viola arvensis, Fumaria officinalis and Ga- lium spurium represent species that were com- mon in cereal-dominated production areas in southern Finland but cannot be successfully con- trolled with sulphonylureas. In general, the in- tensive manipulation of arable land in favour of crops has also favoured species such as Elymus repens and Viola arvensis, which can adapt to the strong competition in cereal stands. In organic farming Chenopodium album, Stellaria media, Galeopsis spp. and Viola arven- sis were found in more than 90% of fields stud- ied. The majority of Finnish organic farms con- verted from conventional to organic cropping after 1995, when Finland became a member of the European Union. Therefore, the botanical composition of fields is still in the process of changing. However, in terms of species diversi- ty, even the short period of organic farming has already been beneficial. Not only did the organ- ic fields have a higher number of weed species but the sprayed conventional and organic fields differed in the most frequent species. Use of herbicides has been found to reduce the number of species in weed communities (Hyvönen and Salonen 2002). In general, farmers should consider some kind of weed control during the growing season, as the weed infestation on organic farms was fairly high and hardly any direct control meas- ures were carried out. Particularly, perennial weed species such as Elymus repens, Sonchus arvensis and Cirsium arvense may threaten the future of organic cereal production if their con- trol is not given due consideration in crop rota- tion. Of interest is that these perennial species were not particularly common in a recent Swed- ish survey of organic farms (Rydberg and Mil- berg 2000). Taking into consideration the frequency and biomass production of weed species, Elymus re- pens is by far the most harmful weed species for spring cereals in Finland. Glyphosate is one of the best selling herbicides in this country (Londe- sborough et al. 2000) but the conditions for spraying are often unsuitable and its efficacy on E. repens is seldom optimal as it is mostly ap- plied on stubble after harvest in September. In conclusion, economy was the driving force in the decision-making of crop production in the 1990s. Indirectly, this is reflected in weed floras now that organic farming has become a common practice and the inputs for cereal production are judiciously considered in conventional farming, too. The decrease in cropping intensity gives weeds an opportunity to make a comeback. Acknowledgements. The weed survey was part of the Finn- ish Biodiversity Programme’s (FIBRE) project “Biodiver- sity in agricultural environments” coordinated by Dr. Juha Tiainen. FIBRE is a comprehensive six-year research pro- gramme launched in Finland in 1997 (see Walls et al. 1999). We thank farmers who allowed us to visit their fields and provided us with information about their farming practic- es. Our permanent survey staff, Eira-Maija Tanni, Anne Muotila and Riina Paju, and a team of field assistants are acknowledged for their intensive toil. Constructive remarks from two anonymous referees are acknowledged. The sur- vey was financed by MTT Agrifood Research Finland and the Ministry of Agriculture and Forestry. 363 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 347–364. References Hynninen, E.-L. & Blomqvist, H. 1997. Pesticide sales continue to slide as planned. Kemia – Kemi 24: 514– 517. Hyvönen, T. & Salonen, J. 2002. Weed species diversity and community composition in cropping practices at two intensity levels – a six-year experiment. Plant Ecology (in press). Jaccard, P. 1912. 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Weeds in spring cereals in Finland SELOSTUS Kolmas kevätviljapeltojen rikkakasvikartoitus Jukka Salonen, Terho Hyvönen ja Heikki Jalli MTT (Maa- ja elintarviketalouden tutkimuskeskus) Kevätviljapeltojen rikkakasvillisuutta kartoitettiin Etelä- ja Keski-Suomessa vuosina 1997–1999 yhteen- sä 16 tutkimusalueella. Aineistoa kerättiin tavanomai- sesti ja luonnonmukaisesti viljellyiltä pelloilta. Tut- kimuksessa oli mukana yhteensä 690 peltoa. Rikka- kasvien tiheys laskettiin kymmeneltä ja kuivapaino määritettiin neljältä 0,1 m2 (40 × 25 cm) laskentaruu- dulta. Pienet laskentaruudut olivat osa 1,0 m2 näyte- alaa, jolta havainnoitiin lajien esiintyminen 0/1-as- teikolla. Näytteet kerättiin heinäkuun puolivälin ja elokuun alkupuolen välisenä aikana. Vastaavat kar- toitukset on tehty 1960- ja 1980-luvun alussa. Kevätviljapelloilta löydettiin yhteensä 188 rikka- kasvilajia (1,0 m2 havaintoalat). Varsinaisilta näyte- aloilta (0,1 m2) löytyi 160 kasvilajia, joista 134 oli leveälehtisiä ja 26 heinämäisiä rikkakasveja. Tavan- omaisesti viljeltyjen torjunta-aineilla ruiskutettujen peltojen yleisimmät rikkakasvit olivat pelto-orvokki (81 % tutkituista pelloista), pihatähtimö (65 %), pil- likkeet (60 %), jauhosavikka (53 %), linnunkaali (52 %) ja pihatatar (50 %). Luonnonmukaisesti vil- jeltyjen peltojen yleisimmät lajit olivat puolestaan jauhosavikka (96 %), pihatähtimö (95 %), pillikkeet (93 %), pelto-orvokki (93 %), peltohatikka (83 %) ja peltoukonnauris (82 %). Yleisin heinämäinen rikka- kasvi oli juolavehnä, jota tavattiin 60 % tavanomai- sen viljelyn pelloista ja 81 % luomupelloista. Kaik- kiaan 18 rikkakasvilajia oli sellaisia, joita löydettiin vähintään joka kolmannelta tutkitulta pellolta. Kes- kimääräinen lajimäärä kaikilla pelloilla oli 18. Luon- nonmukaisesti viljellyillä pelloilla keskimääräinen la- jimäärä oli 24 ja tavanomaisesti viljellyillä 16 (ruis- kutetuilla 15 ja ruiskuttamattomilla 25). Ruiskutetuilla tavanomaisen viljelyn pelloilla kasvoi rikkakasveja keskimäärin 136 kpl/m2, ruiskut- tamattomilla 420 kpl/m2 ja luonnonmukaisesti viljel- lyillä pelloilla 469 kpl/m2. Rikkakasvien tuottama biomassa oli vastaavasti 163 kg/ha, 605 kg/ha ja 678 kg/ha. Rikkakasvien osuus kevätviljapeltojen kasvi- massasta (vilja + rikkakasvit) oli ruiskutetuilla tavan- omaisen viljelyn pelloilla keskimäärin 3 % ja luomu- pelloilla 17 %. Juolavehnä tuotti eniten biomassaa. Rikkakasveja kasvoi viljapelloilla runsaammin kuin 1980-luvun alussa, jolloin edellinen kartoitus tehtiin. Yleisimmät rikkakasvit ovat tavanomaisessa viljelyssä pääosin samoja lajeja kuin 1980-luvulla, mutta esim. juolavehnä on yleistynyt ja runsastunut. Tavanomaisessa viljelyssä on kymmenen yleisimmän lajin joukossa mm. pelto-orvokki, pihatatar, peltoma- tara ja peltoemäkki, joiden kemiallinen torjunta vaa- tii erikoisaineita. Luonnonmukaisen viljelyn yleisty- misen myötä pelloille näyttävät palaavan sellaiset la- jit kuin peltohatikka ja peltoukonnauris sekä kesto- rikkakasveista peltovalvatti ja pelto-ohdake, jotka ta- vanomaisessa viljelyssä saadaan pidettyä kurissa ke- miallisella torjunnalla ja viljan kilpailukyvyllä. Vil- jelyn voimaperäisyys tulee vaikuttamaan rikkakasvil- lisuuden tulevaan kehitykseen. A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Appendix 1 Frequency (% in parentheses) of additional weed species found by region. VERCH (8), ALOPO (4), AGSSS (4), AGSTE (4), ARBTH (4), BARVU (4), BETSS (4), CENCY (4), CIRSS (4), CMPRA (4), DECCA (4), EPIPA (4), KNAAR (4), LYSVU (4), MENAR (4), PIEAB (4), PIUSI (4), PTLAN (4), RUBID (4), SILVU (4), VICSE (4), VICSS (4) Mikkeli (42 fields) HORVS (26), ARTVU (21), URTDI (21), RUMLO (12), SAIPR (12), VERSS (12), AGSSS (10), ALOAE (10), EPISS (10), PHLPR (10), PTLNO (10), STAPA (10), TRFPR (10), ACHPT (7), AVESA (7), BIDTR (7), MENSS (7), RORIS (7), VICSS (7), VIOPA (7), ALCSS (5), ANKSY (5), BRSRA (5), CHERU (5), CHYLE (5), EPIPA (5), FESSS (5), RAPRA (5), SOLTU (5), VERAG (5), AEOPO (2), ATXPA (2), BIDRA (2), DECCA (2), EQUSY (2), FESPR (2), GAGSS (2), GALUL (2), LEBAU (2), LINVU (2), MENAR (2), OXAAC (2), PIBSA (2), POAPA (2), POASS (2), POLSS (2), PTLAN (2), PTLER (2), RUBID (2), RUMSS (2), TRZAS (2), VERCH (2), VICHI (2) Paimio/Tarvasjoki (73 fields) SONAS (40), PLALA (12), ALOGE (8), BIDTR (8), MYSMI (8), CHYLE (7), CERAR (5), LIUUT (5), POLVI (5), RUMLO (5), TRFPR (5), BRSNN (4), BRSRA (4), CIRPA (4), SCRAN (4), AVESA (3), CHEPO (3), CIRHE (3), EPISS (3), FESSS (3), RANSS (3), RAPRA (3), SAIPR (3), SONOL (3), SONSS (3), ANKSY (1), ANTTI (1), ARTVU (1), ATXPA (1), EPIMO (1), EQUSS (1), EQUSY (1), FESPR (1), FIIUL (1), GALPA (1), HORVS (1), LEBAU (1), LOLSS (1), LTHLI (1), PHLPR (1), PIEAB (1), PIUSI (1), POAPR (1), POGSS (1), POLSS (1), SOLSS (1), STAPA (1), VERAG (1), VICSS (1), VIOPA (1) Laihia (42 fields) POAPR (21), ALOGE (7), POATR (7), PHLPR (5), BARVU (2), CIRHE (2), CVPTE (2), DECCA (2), FESSS (2), GEURI (2), PLALA (2), POASS (2), SONAS (2), STAPA (2), TRFPR (2) Nivala (31 fields) BARVU (42), PHLPR (26), ALOPR (23), POASS (23), LEBAU (19), DECCA (16), BIDSS (6), BRSRA (6), EPISS (6), ALOGE (3), ARTVU (3), BETSS (3), BIDRA (3), BRASS (3), FESPR (3), FIIUL (3), MENAR (3), POAPR (3), POATR (3), VIOPA (3) Laitila (51 fields) ARTVU (20), AVEFA (16), CHEPO (12), BIDTR (10), CIRVU (8), RAPRA (6), SENVU (6), SONAS (6), ALOGE (4), CIRHE (4), EPIMO (4), GEURI (4), PHLPR (4), PIUSI (4), STASI (4), TRFPR (4), VIOPA (4), AGSTE (2), Jokioinen (62 fields) POLVI (24), RANSS (11), PTLAN (8), LIUUT (6), ACHPT (5), SENVU (5), RAPRA (3), BARVU (2), BIDTR (2), FAGES (2), FIIUL (2), RUMLO (2), SONSS (2), TRFPR (2), VICSA (2), VIOPA (2) Lammi (63 fields) VICSS (13), PHLPR (10), ARTVU (8), CHERU (6), STAPA (6), URTDI (6), PTLAN (5), BIDSS (3), LEBAU (3), POATR (3), RUMSS (3), SCRAN (3), ACHPT (2), ALOGE (2), AVEFA (2), CIRVU (2), LINVU (2), MENSS (2), RAPRA (2), SOLTU (2), SONAS (2), VERSS (2) Nauvo/Korppoo (40 fields) VICSS (28), TRFPR (18), EPHHE (15), BIDTR (10), PHLPR (5), SONAS (5), VERSS (5), ALOMY (3), CENCY (3), CHYLE (3), GERSY (3), LIUUT (3), MATCH (3), POLSS (3), POLVI (3), RUMCR (3), SOLNI (3) Tammela (53 fields) BIDTR (15), URTDI (13), ARTVU (11), ALOGE (9), SCRAN (9), POLVI (8), PTLAN (8), RUMLO (8), AVESA (6), BARVU (6), EPISS (6), HORVS (6), PHLPR (6), RAPRA (6), STAPA (6), VERSS (6), ALOPR (4), CENCY (4), CERAR (4), DECCA (4), LEBAU (4), PIEAB (4), RANSS (4), RUBID (4), SAIPR (4), SAXSS (4), SENVU (4), THCFL (4), VERAG (4), VICSS (4), VIOPA (4), ACHPT (2), AEOPO (2), ALOMY (2), ALSPA (2), ANRSY (2), BIDSS (2), CIRVU (2), EPHHE (2), EPIPA (2), EQUPA (2), FAGES (2), LINVU (2), LIUUT (2), MEDSS (2), POAPR (2), PTEAL (2), RORIS (2), SOLSS (2), SONAS (2), SONOL (2), STEGR (2), VICVI (2) Laukaa/Toivakka (46 fields) HORVS (22), SAIPR (22), ACHPT (13), EPIPA (13), URTDI (13), LEBAU (11), PHLPR (11), CHEPO (9), RUMLO (9), VIOPA (9), RAPRA (7), SCRAN (7), ALOGE (4), AVESA (4), BIDTR (4), BRASS (4), CHERU (4), FESSS (4), POAPR (4), VERAG (4), ACRPL (2), AGSTE (2), ARBTH (2), BARVU (2), BIDRA (2), CHYLE (2), CIRPA (2), FIIUL (2), GALPA (2), GEURI (2), LIUUT (2), MYSMI (2), PIUSI (2), VICSS (2) Kitee (24 fields) SAIPR (33), TRFPR (33), URTDI (33), BIDRA (29), HORVS (25), RANSS (25), RORIS (25), LEBAU (21), EPISS (17), FESPR (17), PHLPR (17), RUMLO (17), VIOPA (17), ALCSS (13), ALOAE (13), ARTVU (13), CIRVU (13), GALUL (13), POASS (13), VERSS (13), VIOTR (13), ACHPT (8), ANKSY (8), CHYLE (8), CLTPA (8), FAGES (8), LINSS (8), PTLNO (8), RAPRA (8), CONAR (2), FIIUL (2), GALTF (2), LEBAU (2), PLALA (2), RUMLO (2), THLCA (2), URTDI (2), VERAG (2), VIOTR (2) Nurmijärvi (43 fields) SONAS (12), CHEPO (9), STAPA (9), ARTVU (7), PHLPR (7), ALOGE (5), BIDTR (5), LEBAU (5), POASS (5), FESPR (2), GALTF (2), LINVU (2), RAPRA (2), SCRAN (2), SENVU (2), URTDI (2) Vieremä (26 fields) RORSY (35), PHLPR (27), ACHPT (19), EPIPA (19), AVESA (15), PIEAB (12), RUMLO (12), SAIPR (12), VERSS (12), ALCSS (8), ALOGE (8), BIDTR (8), CHYLE (8), CHYVU (8), LEBAU (8), PIUSI (8), POAPR (8), SONAS (8), VERAG (8), CENCY (4), CIRHE (4), CMPPA (4), EQUSY (4), GEURI (4), HORVS (4), RANAU (4), STAPA (4), STEGR (4), TRFPR (4), URTDI (4), VICSS (4), VIOPA (4) Kihniö/Parkano (33 fields) HORVS (42), EPIPA (33), ALOGE (30), SAIPR (21), VIOPA (21), PHLPR (18), RUMLO (18), CIRPA (15), POAPR (12), ARTVU (9), CHYLE (9), PIEAB (9), ACHPT (6), BIDTR (6), PIUSI (6), URTDI (6), AEOPO (3), AGSSS (3), AGSTE (3), ALOPR (3), AVESA (3), CENCY (3), LEBAU (3), RUBID (3), TRFHY (3) Iitti (35 fields) TRFPR (20), STAPA (17), PHLPR (11), VICSS (11), CENCY (9), PIUSI (9), ALOGE (6), ARTVU (6), POAPR (6), AGSGI (3), ALOPR (3), BETSS (3), CENJA (3), CHEPO (3), CHERU (3), EPIPA (3), FESOV (3), LEBAU (3), POLSS (3), PTLAN (3), RANSS (3), RAPRA (3), RUMCR (3), RUMSS (3), VERSS (3), VICHI (3), VIOPA (3) Imatra/Ruokolahti (26 fields) LEBAU (23), ARTVU (19), PHLPR (19), VICHI (19), ACHPT (15), RAPRA (15), PIUSI (12), ALCSS (8), BIDSS (8), CHERU (8), LINVU (8), MENAR (8), RORIS (8), SCRAN (8), URTDI (8), VIOPA (8), ALOGE (4), ALOPR (4), AVEFA (4), CHEPO (4), CHYLE (4), EPIPA (4), EPISS (4), EROCI (4), GEURI (4), HYPPE (4), LOLPE (4), PIBSA (4), POAPR (4), PTLAN (4), PTLNO (4), RANSS (4), RUMCR (4), RUMSS (4), TRFHY (4), TRFPR (4), VICSS (4) Key of Bayer code abbreviations: ACHMI Achillea millefolium, ACHPT Achillea ptarmica, ACHSS Achillea spp., ACRPL Acer platanoides, AEOPO Aegopodium podagraria, AGRRE Elymus repens, AGSSS Agrostis spp., AGSTE Agrostis capillaris, ALCSS Alchemil- la spp., ALOAE Alopecurus aequalis, ALOGE Alopecurus geniculatus, ALOMY Alopecurus myosuroides, ALOPR Alopecurus pratensis, ALSPA Alisma plantago-aquatica, ALUSS Alnus spp., ANKSY Angelica sylvestris, ANRSY Anthriscus sylvestris (silvestris), ANTTI Anthemis tincto- ria, ARBTH Arabidopsis thaliana, ARTVU Artemisia vul- garis, ATXPA Atriplex patula, AVEFA Avena fatua, AVESA Avena sativa, BARVU Barbarea vulgaris, BETSS Betula spp., BIDRA Bidens radiata, BIDSS Bidens spp., BIDTR Bidens radiata, BRASS Brachiaria spp., BRSNN Brassi- ca napus L. var. oleifera, BRSRA Brassica rapa, BRSRO Brassica rapa L. ssp. oleifera, CAPBP Capsella bursa- pastoris, CENCY Centaurea cyanus, CERAR Cerastium arvense, CERFO Cerastium fontanum, CHAAN Epilobium angustifolium, CHEAL Chenopodium album, CHEPO Chenopodium polyspermun, CHESS Chenopodium spp., CHYLE Leucanthemum vulgare, CIRAR Cirsium arven- se, CIRHE Cirsium helenioides, CIRPA Cirsium palustre, CIRSS Cirsium spp., CIRVU Cirsium vulgare, CLTPA Callitriche palustris, CMPRA Campanula rapunculoides, DECCA Deschampsia cespitosa, EPHHE Euphorbia helio- scopia, EPIMO Epilobium montanum, EPIPA Epilobium palustre, EPISS Epilobium spp., EQUAR Equisetum ar- vense, EQUPA Equisetum palustre, EQUSS Equisetum spp., EQUSY Equisetum sylvaticum, CHYVU Tanacetum vul- gare, ERYCH Erysimum cheiranthoides, FAGES Fagopyrum esculentum, FESPR Festuca pratensis, FESSS Festuca spp., FIIUL Filipendula ulmaria, FUMOF Fumaria officinalis, GAEBI Galeopsis bifida, GAESP Galeopsis speciosa, GAESS Galeopsis spp., GAETE Galeopsis tet- rahit, GAGSS Galega spp., GALPA Galium palustre, GALSP Galium spurium, GALSS Galium spp., GALUL Galium uliginosum, GERSY Geranium sylvaticum, GEURI Geum rivale, GNAUL Gnaphalium uligonosum, HORVS Hordeum vulgare, spring barley, IUNBU Juncus bufonius, KNAAR Knautia arvensis, LAMAL Lamium album, LAMPU Lamium purpureum, LAMSS Lamium spp., LAPCO Lapsana communis, LEBAU Leontodon autum- nalis, LINSS Linaria spp., LINVU Linaria vulgaris, LIUUT Linum usitatissimum, LOLSS Lolium spp., LTHLI Lathy- rus linifolius, LTHPR Lathyrus pratensis, LYSVU Lysi- machia vulgaris, MATCH Matricaria chamomilla (recuti- ta), MATIN Tripleurospermum inodorum, MATMT Mat- ricaria matricarioides, MATSS Matricaria spp., MEDSS Medicago spp., MENAR Mentha arvensis, MENSS Men- tha spp., MYOAR Myosotis arvensis, MYSMI Myosurus minimus, OXAAC Oxalis acetosella, PHLPR Phleum prat- ense, PIBSA Pisum sativum L. var. arvense, PIEAB Picea abies, PIUSI Pinus silvestris (= sylvestris), PLALA Plan- tago lanceolata, PLAMA Plantago major, POAAN Poa annua, POAPA Poa palustris, POAPR Poa pratensis, POASS Poa spp., POATR Poa trivialis, POGSS Polygala spp., POLAV Polygonum aviculare, POLCO Fallopia con- A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Appendix 1 volvulus, POLHY Persicaria hydropiper, POLLA Persicar- ia lapathifolium, POLPE Persicaria maculosa, POLSS Polygonum spp., POLVI Bistorta vivipara, PRNPA Pru- nus padus, PTEAL Pteridium aquilinum, PTLAG Poten- tilla argentea, PTLAN Potentilla anserina, PTLER Po- tentilla erecta, PTLNO Potentilla norvegica, RANAC Ra- nunculus acris, RANRE Ranunculus repens, RANSS Ranunculus spp., RAPRA Raphanus raphanistrum, RORIS Rorippa palustris, RUBID Rubus idaeus, RUMAA Rumex acetosella, RUMAC Rumex acetosa, RUMCR Rumex cris- pus, RUMLO Rumex longifolius, RUMSS Rumex spp., SAIPR Sagina procumbens, SAXSS Salix spp., SCRAN Scleranthus annuus, SECCE Secale cereale, SENVU Sene- cio vulgaris, SILVU Silene vulgaris, SOLNI Solanum ni- grum, SOLSS Solanum spp., SOLTU Solanum tuberosum, SONAR Sonchus arvensis, SONAS Sonchus asper, SONOL A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Appendix 1 Sonchus oleraceus, SONSS Sonchus spp., SPRAR Sper- gula arvensis, STAPA Stachys palustris, STEGR Stellaria graminea, STEHO Stellaria holostea, STEME Stellaria media, TAROF Taraxacum officinale, THCFL Thalictrum flavum L. ssp. flavum, THLAR Thlaspi arvense, TRFPR Trifolium pratense, TRFRE Trifolium repens, TRFSS Tri- folium, TRZAS Triticum aestivum, spring wheat, TTTDD Dicot weed species, TTTMM Monocot weed species, TUSFA Tussilago farfara, URTDI Urtica dioica, VERAG Veronica agrestis, VERCH Veronica chamaedrys, VERSE Veronica serpyllifolia, VERSS Veronica spp., VICCR Vi- cia cracca, VICHI Vicia hirsuta, VICSA Vicia sativa, VICSE Vicia sepium, VICSS Vicia spp., VICVI Vicia vil- losa ROTH ssp. villosa, VIOAR Viola arvensis, VIOPA Viola palustris, VIOSS Viola spp., VIOTR Viola tricolor L. ssp. tricolor Title Introduction Material and methods Results Discussion References SELOSTUS Appendix 1