Maataloustieteellinen A ikakauskirja
Voi 61: 15—31, 1989

Yield, its components and pest incidence in mixed intercropping
of oats (Avena sativa) and field beans (Vida faba)

JUHA HELENIUS and PÄIVI RONNI

Department of Agricultural and Forest Zoology, University of Helsinki,
SF-00710 Helsinki, Finland

Abstract. Seed yields, yield components, pest incidence and damage were examined in two
field experiments of mixed intercropping of oats (A vena saliva) with field beans (Vida faba)
in Southern Finland in 1984—1985.The stand types were monocrops and replacement series
of mixtures with 2/3 and 1/3 or 1/3 and 2/3 of oats and beans, respectively, on plots treated
or not treated with insecticide.

In the first season when the overall performance of the crops was poor and the numbers
of the main pest Rhopalosiphum padi (Horn., Aphididae) on oats low, the Land Equivalent
Ratio (LER) index indicated an intercroppingadvantage in the bean yield and a disadvantage
in the oat yield, the insecticide treatment having no effect on the overall nor on the relative
performance of the component crops. The site used during the second season was of high fer-
tility, thus favouring oats over beans. The LERs indicated no advantage or disadvantage in
mixed cropping for either oats or beans when R. padi was not controlled. Spraying against
R. padi improved the performance of oats, the mixture with 1/3 oats showing an advantage
over the monocrop. Simultaneously, there were signs (p=0.08) of a reduction in the relative
performance of the beans. The indicative results support the hypothesis of interspecific dy-
namics in compensatory yielding as an element of improved reliability in intercropping.

The yield components most sensitive to the change in cropping pattern were the number
of panicles per plant in oats and the seed weight in beans, both increasing in the mixtures.
Compared toknown responses to stand density in monocrops, the beans responded to the mixed
cropping in a more specific way than the oats.

Mixed cropping increased the numbers of aphids in oats. There were signs of a reduced
incidence, but not of a reduced average colony size, of Aphis fabae, and of a reduced rate
of notching by Silona spp. weevils on beans in mixed cropping. The results for damage by
the frit fly (Oscinella frit) were inconclusive.

Index words: Intercropping, oats, faba bean, yield, yield components, pest numbers, pest damage, Rhopalosiphum padi

15

JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND

https://www.c-info.fi/en/info/?token=zXjsJJ5EenxEBTHE.YZ38bgHTXMtc2Woj8ODnjw.JSY6uk_N9aOUaQikZ35R2uIRdfwBzEoywr8OYHj8EZ6Cs1j0iXezfJnxiChowkfhzzBOfySqC6PcPqi68IEybcIlLWvyTHiqBMH297NfHSYsS5G6ZIMhC04zifcJRxmtQhSo_V_BpF63yJuupfo_45eTcHQsHVxhbBVQrjGob7Tk1Au7yAWRW6j5TXvcRzMa


Introduction

Intercropping can be more profitable than
monocropping in certain systems. The advan-
tages of intercropping are due not only to an
increased total yield per unit area but also to
improved reliability from season to season.
The better yield is generally thought to be
based on complementarity in the use of avail-
able resources; the improvement in reliability
is thought to be due to the compensatory dy-
namics of yield formation in the component
crops (see Willey 1979; also Trenbath
1977). In the case of pest attack or other en-
vironmental stress on one of the components,
the hypothesis of compensation predicts an in-
crease in the yield of the associated compo-
nent (Trenbath 1976, Perrin 1977). The abil-
ity of the associated crop to compensate de-
pends primarily on the timing of damage in
relation to the development stages of the crops
and on the availability of resources for com-
pensatory development and growth.

Intercropping of grain legumes with cereals
has received special attention in research: it
is a widespread practice in many climatic con-
ditions, it produces high nitrogen yields and
it requires low nitrogen inputs. In many cases
intercropping improves the reliability of the
legume component in particular. In the sys-
tem studied by Rao and Willey (1980), i.e.
sorghum/pigeonpea cultivation in India, it
was estimated that monocrops would fail once
in five to eight years, but intercrops in only
one year out of 36. In Finland, intercropping
of a mixture comprising 60—70 % field beans
(Vida faba Linnaeus, Fabaceae) and 30—

40 % oats (A vena sativa Linnaeus, Poaceae)
has given better yield stability as compared to
the monocropping of beans (Varis et ai.
1982). Mixed cropping with oats was recom-
mended by the breeder for the Finnish culti-
vars of faba bean, Mikko and Ukko (Hovi-
nen 1982, 1984).

Intercropping can reduce pest damage (for
reviews see Norton 1975, Litsinger and
Moody 1976, Perrin 1977, Altieri and Lieb-
man 1986). A slight majority of studies report

a decrease rather than an increase in pest num-
bers (Altieri and Letourneau 1982, Risch et
al. 1983, Baliddawa 1985), but the changes
in pest numbers have not been studied suffi-
ciently in relation to the yielding of the crops.
The emphasis of this research should be on
the possibilities of reducing quantitative and
qualitative losses in yield, not on changes in
pest numbers per se.

The purpose of the study reported in this
paper was to elucidate the effects of mixed
cropping on the process of yield formation in
oats and field beans. The results are discussed
with reference to pest incidence and damage.
An attempt was made to test the hypothesis
of compensatory yielding from beans in the
mixtures in case of damage to oats caused by
cereal aphids. Some preliminary findings have
been described earlier by Helenius (1988),
and the increase due to mixed cropping in the
population densities of the main pests in the
system, cereal aphids, was reported separate-
ly (Helenius 1989).

Material and methods

Experimental designs

Monocrops of oats cv. Puhti and field
beans cv. Mikko were compared with mixed
intercrops of these two plants in two field ex-
periments, carried out during 1984 and 1985
in Helsinki. The experiments consisted of four
different crop types:

(1) Monocrop of oats (notation OOO) with
a normal seed density of 500 germinating seeds
per m 2.

(2) A mixture of 2/3 oats and 1/3 beans
(OOB) following the replacement principle
(de Wit 1960, see also Willey 1979): the
monoculture sowing density of field beans was
100 germinating seeds per m 2, and the 008
mixture was established by drilling 2/3 X 500
germinating seeds of oats and 1/3 X 100 ger-
minating seeds of beans per m 2.

(3) A mixture of 1/3 oats and 2/3 beans
(OBB). The 088 mixture was established by

16



following the same replacement principle used
for the 008 mixture.

(4) Monocrop of beans (BBB) with a nor-
mal seed density of 100 germinating seeds
per m 2.

The mixtures were established by drilling
the seed mixture, and in every case the
achieved seedling density was lower than the
targeted one (see Results, Fig. 2). The spac-
ing between rows was 125 mm in all stand
types. The rates of nitrogen fertilization were
80 kg/ha for 000, 40 kg/ha for 008 and
088, and 0 kg/ha for 888.

Experiment I (1984) employed a factorial
split-plot design with crop type as the main
plot factor having four levels, and abundance
of cereal aphids as the sub-plot factor having
two levels (i.e. one not sprayed and one
sprayed with insecticide). The plot size was
10 m x 10 m. The sub-plot in which the cereal
aphids were controlledconsisted of a 2.5 m x
10 m strip running across the plot. In the
spraying 0.75 1/haof dimethoate was applied
on 19 June at oats G.S. 31 (decimal code for
the growth stages of cereals, see Tottman
and Broad 1987), 6 days before the beans
started flowering. There were three replica-
tions (blocks).

Experiment II (1985) followed a complete-
ly randomized block design with three blocks.
All the eight factorial treatment combinations,
i.e. four stand types times two spraying lev-
els (unsprayed or sprayed), were randomized
withineach block on plots 7.3 m long and ten
rows wide (gross width 1.5 m). In the spray-
ings 6.25 g/ha deltamethrin was applied, for
the first time on 20 June at oats G.S. 21 and
for the second time on 3—4 July at oats G.S.
30, the same time as when the first bean flow-
ers opened. Benomyl (750 g/ha) was applied
to protect beans against bean leaf pathogens
(Botrytis cinerea Pers. ex Fr., Ascochyta sp.)
on 3 July over the whole experiment area.

Sampling for pests

In Experiment I the sampling for insect
pests was done in the unsprayed sub-plots

2

only, while in Experiment II the sprayed plots
were also sampled.

Cereal aphid populations were monitored
by taking random samples of 60—400 oat
tillers per plot in situ, usually twice a week.
Care was taken to avoid damaging the tillers
or the insects on the tillers during inspection.
Total numbers and the numbers of alatae
adults of the aphids, Rhopalosiphum padi
(Linnaeus), Sitobion avenae (Fabricius) and
Metopolophium dirhodum (Walker) (Horn.,
Aphididae), were recorded for each tiller sam-
pled. The score estimation method described
by Lowe (1984) was applied in certain cases
in Experiment 11. The cumulative numbers of
R. padi were calculated as aphid days in an
analogous way to degree days (e.g. Ruppel

1983). Mild visible symptoms of barley yellow
dwarf virus (BYDV) were found on 8 % of
the plants in all the stand types when sampled
on 15 August (Experiment I, n = 1 118) and
18 July (Experiment 11, n= 144).

The infestation level was estimated as the
proportion of oat stems infested by Oscinella
frit (Linnaeus) (Dipt., Chloropidae) in Ex-
periment I using guadrat plant samples (2x
0.25 m 2 per plot) on 25 June (G.S. 39). The
same sampling procedure was applied on 23
July (G.S. 70) in order to estimate the infesta-
tion of adventive tillers. As the incidence was
very low, being concentrated on late adven-
tive tillers in particular, it was not estimated
in Experiment 11.

Fifty stems per plot on 18 and 31 July in
Experiment I and 10 stems per plot on 11 July
in Experiment II were sampled for Aphis fa-
bae Scopoli and Acyrthosiphon pisum (Har-
ris) (Horn., Aphididae) on beans. The scores
were estimated in all cases except for A. pisum
in Experiment I, where the numbers were ac-
tually counted.

An estimate of the relative abundances of
bean weevils in the genus Sitona Germar
(Col., Curculionidae) in Experiment I was ob-
tained by comparing the pitfall catches. Pit-
fall trapping was carried out in order to as-
sess the activity abundances of epigeig poly-
phagous predators (in preparation). The traps

17



consisted of two plastic cups (diameter 80 mm)
in the two sub-plots of each plot where the in-
gress of epigeic arthropods was manipulated.
The incidence of notching was low and was
not estimated. No pitfall trapping was carried
out in Experiment 11, and notching by Sitona
was estimated by counting the numbers of
notches in the lowest leaf of at least three
leaflets in a sample of 10 stems per plot.

Analysis of yields

Two 0.25 m 2 quadrats per plot were sam-
pled from Experiment I, and 3 x 1 row meters
of oats, 3x2 row meters of beans per plot
from Experiment 11, in order to estimate the
densities and yield components of oats and
beans just before harvest, at oats G.S. 91.
Only the unsprayed plots were included in Ex-
periment 1.

The plots were harvested using a plot com-
bine. Seed moisture levels were determined at
harvesting in order to estimate the degree of
ripeness. The seed lots were dried, sorted by
species, weighed and, after determinationof
the moisture content, the yields per unit area
at 15 % moisture content calculated. Average
seed weights (1 000 seed weight) were deter-
mined, but only for the unsprayed treatments
in Experiment I. The total nitrogen content
of the seed yields was determined by the Kjel-
dahl method in Experiment 11.

Calculation of the land equivalent ratio,
LER (Willey 1979, Mead and Willey 1980),
was based on the achieved seedling densities,
not on the seeding rates. This was done in
order to improve the biological interpretability
of the LERs. The divisor for the control mix-
tures was the yield of the control monocrop,
and the divisor for the sprayed mixture was

Table 1. Comparison of treatment means of seed yields (kg/ha) of oats and field beans in control plots and plots
sprayed against cereal aphids on the monocrops and the mixtures. Analysis of variance for the treatment effects.

Monocrop 008 mixture 088 mixture
2/3 oats + 1/3 oats +

1/3 beans 2/3 beans

Exp. I (1984)
Oats control 3 074(408) 2 272(663) 828(210)

sprayed 3 465 (157) 2 268 (844) 839 (254)
abc

Beans control 1 169 (322) 736 (251) 1 146 (258)
sprayed 1 027 (302) 857 (210) 1 053 (272)

Exp. II (1985)
Oats control 4 538(730) 2 612(244) 1797(383)

sprayed 5 859 (74) 4 605 (466) 3 056 (212)
abc

Beans control 559 (115) 282 (70) 480 (140)
sprayed 517(118) 178 (50) 330(134)

abb

Analysis of variance: Oats Beans

source year df F-value df F-value
crop type 1984 2/4 31.0*** 2/4 1.2 ns

1985 2/10 63.9 *** 2/10 12.0 **

spraying 1984 1/6 2.3 ns 1/6 0.2 ns
1985 1/10 57.5 *** 1/10 3.7 (*)

interaction 1984 2/6 2.2 ns 2/6 0.9 ns
1985 2/10 1.4 ns 2/10 0.7 ns

block 1984 2/4 2.6 ns 2/4 0.2 ns
1985 2/10 0.5 ns 2/10 1.0 ns

Standard deviations given in brackets. Significant differences between stand types are indicated by letters within-row.

18



the yield of the sprayed monocrop (see Oye-

joea and Mead 1982).

Statistical procedures

Analysis of variance procedures were ap-
plied to the LERs as robust means of com-
parisons (see Oyejola and Mead 1982). Fre-
quency tables for mortality rates (binomial
case with logit link) or pest incidences (Pois-
son case with log link) were analysed by log
linear models (LOGLIN) using the GLIM
package (Baker and Nelder 1978). Student’s
t-test was referred to by lowercase t. 10, 5, 1
and 0.1 °7o risk levels were indicated by (*),

*, ** and ***, respectively. If not reported the
result of the analysis of variance tests for the
interaction term was not significant.

Results

Seed yields

The average monocrop yield of oats in Ex-
periment I was only two thirds of that in Ex-
periment 11, but the average monocrop yield
of beans in Experiment I was twice that in Ex-
periment II (Table 1).

Mixed cropping decreased the yield (kg/ha)
of oats. As expected, the decrease was the
greater the higher the proportion of beans in
the mixture. The yield of beans was not sig-
nificantly reduced in the mixtures in Experi-
ment I, but in Experiment II the absolute yield
of beans was significantly lower in the 008
mixture than in the 088 mixture, or in the
monocrop (Table 1).

In Experiment I the spraying treatment did
not have any significant effect on the yield
of either oats or beans. In Experiment II the
deltamethrin treatment significantly increased
the yield of oats in all the crop types. Howev-
er, there were signs that the spraying reduced
the yields of beans (p =0.08 in the F-test) (Ta-
ble 1). The average increase in the oat yield
and reduction in the bean yield was largest in

the mixtures (proportional change due to
spraying, %):

000 008 088 888
oats +29 +76 +7O
beans —37 —3l —8

However, the interaction of spraying X crop
type was not significant.

The relative performance of oats as meas-
ured by the LER index varied in relation to
the yield level of beans, and it was affected
most in the extreme 088 mixtures. At the
relatively high level in Experiment I, the
LERoats in the 088 mixture was significant-
ly lower than the LER e (i.e. LER exptected
on the basis of the relative seedling density)
(t = 2.63*, df= 5), but at the low level of bean
yield in Experiment II the opposite was true.
In the sprayed 088 mixture the LERoats was
significantly higher than the LER F (t = B.Bo*,
df=2) (Fig. 1). The relative yields in the

Fig. I. Relative (LER) seed yields of oats and beans
plotted against seedling densities in the 008
(sowing rate 2/3 oats + 1/3 beans) and 088
(1/3 oats + 2/3 beans) mixtures in control plots
(open dots) or plots sprayed against cereal aphids
(black dots). Dashed linear lines indicate rela-
tive yields proportional to seedling density, i.e.
no advantage or disadvantage of intercropping
as compared to the case when starting with the
same number of seedlings as a monocrop.

19



sprayed mixtures were higher than the relative
yields in the control mixtures for all crop types
(F= 16.99**, df= 1,6).

The relative performance of the beans was
significantly improved by mixed cropping in
Experiment I, where the LERbeans in the 008
mixture was significantly higher than the
LER e (t = 4.39**, df=s) (Fig. 1). In Experi-
ment II the LER values for beans did not sig-
nificantly deviate from the expectations. How-
ever, there were signs that spraying reduced
the LERbeans (F = 4.47, p = 0.08, df= 1,6)
(Fig. 1).

Yield components in oats
In Experiment I there was significant mor-

tality from seedling stage to harvest (F =

36.1***, df=l,6). The estimated mortality
rates were 40 % in the monocrop, 35 % in the
008 and 32 % in the 088 mixture (F =

4.2(*), df= 2,6) (Fig. 2).
The number of panicles per plant increased

with a decreasing proportion of oats in the
stand (F = 62.5**, df= 2,4): on an average
34.2 %, 39.4 % and 46.5 % of the panicles
were on adventive tillers in the monocrop, in
the 008 mixture and in the 088 mixture,
respectively (Fig. 3). Tillers consistently
produced smaller panicles: on an average 27.6
grains/panicle (SE = 1.8, n = 9) as opposed to

46.6 grains/panicle (SE =2.8, n= 9) (F =

74.0***, df = 1,6) for the main stem. In Ex-
periment I, the average size of the panicles on
the main or adventive stems (as number of
grains per panicle) was not influenced by in-
tercropping (F =0.5 n.s., df= 2,4).

In Experiment 11, the average size of the
panicles was 40.1 grains/panicle (SE=l.O,
n= 3) in the unsprayed monocrop, 42.3
(SE = 2.5) in the unsprayed 008 mixture and
47.0 (SE = 1.0) in the unsprayed 088 mixture,
but 45.5 (SE = 0.8) in the sprayed monocrop,
51.0 (SE = 0.5) in the sprayed 008 mixture
and 54.4 (SE= 1.8) in the sprayed 088 mix-
ture. Thus, the panicle size was increased up
to 18 % by intercropping (F = 6.0*, df= 1,6).
Spraying against cereal aphids increased the
panicle size by 16 ®/o (F= 19.9**, df= 1,6) in
all crop types.

Neither mortality nor tillering of oats were
measured in Experiment 11. The density of the
panicles in relation to seedling density was
1.00 (SE = 0.06, n =6) in the monocrop, 1.02
(SE = 0.06) in the 008 mixture and signifi-
cantly greater, 1.36 (SE = 0.08), in the 088
mixture (F = 46.0***, df = 2,10). As a result
of mortality after seedling emergence, these
figures are likely to underestimate the forma-
tion of panicle-bearing tillers per surviving
plant. The relative differences between stand
types in the densities of harvestable panicles
were less than those in the seedling densities
(Fig. 4).

Spraying significantly increased the ratio
between panicle density and seedling density
by 15 %, irrespective of stand type (F =

Fig. 2. Seedling densities (open bars) and densities at
harvest (dotted bars) of oats and beans, and
harvestable densities of beans (dark bars) in the
monocrops and mixtures (Experiment I). (Oats
monocrop, mixture with 2/3 oats and 1/3 beans,
mixture with 1/3 oats and 2/3 beans and beans
monocrop are indicated by 000, 008, 088
and 888, respectively. Vertical lines indicate
S.E.)

Fig. 3. Number of adventitious tillers bearing panicles
per plant in oats in the monocrop and mixtures
(Experiment I). (Vertical lines indicate S.E.)

20



21

20.9***, df= 1,10). Correspondingly, the es-
timated increase due to spraying in the num-
ber of panicles per unit area was 14 % (F =

10.8**, df= 1,10) in all crop types (Fig. 4).
The 1 000 seed weight (after sorting) was

not influenced by intercropping. In Experi-
ment I the average was 36.1 g. In Experiment
11 the sprayings significantly increased the
1 000 seed weight by 7.3 °/o: on the control
plots the average was 30.2 g (SE = 0.40, n = 9)
and on the sprayed plots 32.4 g (SE = 0.48,
n = 9) (F = 18.2**, df = 1,10).

Yield components in beans

The secondary shoot formation of the beans
was negligible and the density of the stems
reflected the total density of beans in autumn.
In Experiment I, the mortality rate of the
beans from seedling stage to harvest averaged
27 »/o (F = 5,4(*), df = 1,6) (Fig. 2) and in Ex-
periment II it averaged 21 % (determined
as loss of stems from seedling stage to har-
vest) and was significant (F = 18.3*, df= 1,4,
Fig. 4). The mortality did not depend on stand
type (Experiment I, F = 2.0 n.s., df = 2,6; Ex-
periment 11, F = 2.2 n.s., df= 2,4). Spraying
against cereal aphids had no effect on mor-
tality (Experiment 11, F = 0.02 n.s., df= 1,4).

In Experiment I there was an additional loss
of pod-bearing stems due to lodging and sub-
sequent rotting of 42 % in the monocrop,
35 % in the 088 mixture and 17 % in the

008 mixture. Mixed cropping reduced the
rate of lodging significantly (LOGLIN, logit,
AG 2

= 7.6*, df= 2). Owing to plant mortality
or losses due to lodging, the harvestable den-
sity of the beans was not significantly higher
in the monocrop than in the mixtures (F =3.8
n.s., df=2,4). The losses of beans were rela-
tively higher in the monocrop than in the mix-
tures (Fig. 2).

The number of pods per stem did not vary
significantly between stand types. In Experi-
ment I the average number was 9.4, in the
lodged plants only 3.2. Thus, the loss in yield
due to lodging was relatively less than the loss
in density due to lodging. In Experiment II the
number of pods averaged 6.2 (SE = 0.4, n = 9)
in the control plots and 4.7 (SE = 0.4, n = 9)
in the sprayed plots: deltamethrin sprayings
significantly reduced pod formation (F =

14.2**, df= 1,10).
The number of seeds per pod in the har-

vestable beans averaged 3.2 and 2.3 in Experi-
ments I and 11, respectively. The pod size was
not affected by intercropping (Experiment I,
F = 0.03 n.s., df= 2,4; Experiment 11, F = 0.3
n.s., df= 1,6) or by sprayings (Experiment 11,
F =0.4 n.s., df = 1,6).

The 1 000 seed weight was highest in the
008 mixture and decreased significantly with
an increasing proportion of beans in the stand
(Experiment I, F= 196.6***, df= 2,4; Experi-
ment 11, F = 13.4**, df= 2,10). It was not af-
fected by the aphicide sprayings (F =0.0 n.s.,
df= 1,10) (Fig. 5).

Fig. 4. Seedling densities (open bars), densities of stems
bearing panicle in oats not sprayed (dotted bars)
or sprayed (dark bars) against cereal aphids, and
densities of harvestable stems in beans (dotted
bars) in the monocrops and mixtures (Experi-
ment II). (Vertical lines indicate S.E.)

Fig. 5. The 1 000 seed weight of beans in the final yield
in the monocrop and mixtures (Experiments I
and II). (Vertical lines indicate S.E.)



Nitrogen Yield

Data were obtained from Experiment II
only. Mixed intercropping slightly but signifi-
cantly increased the total nitrogen content of
the oat (F = 6.3*, df = 2,10) and bean seeds
(F = 9.6**, df = 2,10). Deltamethrin treatment
had no effect on the nitrogen content of the
beans (F = 0.0 n.s., df= 1,10) but decreased
that of the oats significantly (F = 25.9***,
df= 1,10), by 12 % in all stand types (inter-
action crop type x treatment not significant,
F = 0.0 ns, df= 2,10) (Fig. 6).

The increase in the oat seed yield more than
compensated for the lower nitrogen content
in the sprayed plots. The highest total nitro-
gen yield, as estimated from the average seed
yields and nitrogen contents, was obtained
from the sprayed monocrop of oats, the
lowest from the sprayed monocrop of beans
(Table 2).

Crop maturity

An indirect estimate of crop maturity at
harvest was obtained by measuring the mois-
ture content of the seeds.

In Experiment I the seed moisture content
averaged 30.4 % (SE = 0.7, n = 9) in oats and
42.3 °7o (SE =0.9) in beans. There were no
statistically significant differences between
stand types (oats F = 1.1 n.s.; beans F = 0.8
n.s., df= 2,8). In Experiment 11, the moisture
content of oats at harvest was significantly in-
creased by intercropping (F=l7.4***, df=

2,10). Spraying slightly but significantly
reduced the moisture content at harvest,
equally in all stand types (F = 6.0*, df= 1,10).
The moisture content in beans was significant-
ly decreased by intercropping (F = 27.8***,
df=2,10); but was not affected by spraying
(F =0.6 n.s., df= 1,10) (Fig. 7).

Table 2. Nitrogen yields (kg/ha) as calculated by multiplying the treatment means of seed yields by the means of
seed nitrogen content (proportion of total N) in control (C) and sprayed (S) plots on the monocrops and the mixtures.

Oats 008 mixture 088 mixture Beans
monocrop 2/3 oats + 1/3 oats + monocrop

1/3 beans 2/3 beans

cs cs cs cs
Oats 96 108 56 89 42 63
Beans 14 9 23 16 26 24
Total 96 108 70 98 65 79 26 24

Data were obtained from Experiment II only.

22

Fig. 6. Total nitrogen content (%) in oat seeds not
sprayed (open bars) or sprayed against cereal
aphids (dotted bars), and in bean seeds in the
monocrops and mixtures (Experiment II). (Ver-
tical lines indicate S.E.)

Fig. 7. Moisture content (% water) at harvest in oat
seeds not sprayed (open bars) or sprayed against
cereal aphids (dotted bars), and in bean seeds in
the monocrops and mixtures (Experiment 11).
(Vertical lines indicate S.E.)



Pest incidence

Experiment I. The most abundant cereal
aphid on oats was R. padi. M. dirhodum also
reached relatively high densities (Table 3). The
peak densities of R. padi occurred after the
anthesis, around mid July. Stand type had no
consistent influence on the peak densities
(analysis of variance using plot means, In-
transformation: R. padi F = 1.1 ns, M. dirho-
dum F = 0.7 ns, df= 2,4). The cumulative
number of aphid-days for R. padi reached
150—250 per tiller by August, and they were
still slowly increasing at that time. There were
no significant differences between stand types
(F = 2.2 ns, df=2,4) (Fig. 8).

Frit fly (O. frit) infestation was severe and
averaged 48.6 °7o (proportion of yellowed
main stems) at G.S. 39; at that time it was not
affected by the cropping pattern to any con-
sistent degree (the interaction crop X block
was significant; LOGLIN, logit AG 2

= 12.1*,
df= 4). Four weeks later, at G.S. 70, the esti-
mated infestation on the adventive tillers aver-
aged 36 % (proportion of yellowed tillers) in
the monocrop, 30 % in the 008 mixture and
26 % in the 088 mixture (LOGLIN, logit,
AG 2 = 8.3*, df = 2).

On beans, A. fabae was more frequent in
the monocrop than in the mixtures. The inci-
dence, expressed as the proportion of infest-
ed tillers, increased from 18 to 31 July by 30 %

in the monocrop, 227 % in the 088 mixture
and 131 % in the 008 mixture (LOGLIN,
logit, AG 2 = 26.9***, df= 1). On 18 July the
incidences were 66 % and 70 % lower, and
on 31 July 14 % and 47 °7o lower in the 088
and 008 mixtures than in the monocrop
(LOGLIN, logit, AG 2 = 32.2***, df=2, inter-
action crop x date AG 2 = 7.6*, df=2). The
colony size of A. fabae, estimated from the
score samples, did not increase significantly
from 18 to 31 July (F =2.4 ns, df= 1,2). The
colony size averaged 544 specimens per stem

Table 3. A: Means of the peak densities of R. padi per tiller (n= 150) and highest observed numbers of S. avenae
and M. dirhodum per tiller of oats on the monocrop and the mixtures (Experiments I and II). B: Comparison of
mean numbers per tiller in control plots (C) and plots sprayed against cereal aphids (S) on 9 July, five days after
the last spraying (Experiment 11).

A: R. padi S. avenae M. dirhodum

Exp. I Exp. II Exp. I Exp. II Exp. I Exp. II
mean (SE) mean" mean mean mean mean

monocrop 13.3(1.2) 25.31.7 0.25.6 1.5
008 mixture 9.9(1.2) 29.82.1 0.16.8 0.9
088 mixture 16.0 (1.5) 32.5 K 2 (U 8J? 1.0

B: R. padi S. avenae M. dirhodum

C S C S C S
mean (SE) mean (SE) mean mean mean mean

monocrop 11.5(1.8) 3.1(0.8) 0 0 0.81.2
008 mixture 19.0 (2.7) 3.8 (0.9) 0 0 0.80.6
088 mixture 33.4(6.2) 7.9(1.2) 0 0
' score estimation 2 —5 July
OOB: 2/3 oats + 1/3 beans; 088 1/3 oats + 2/3 beans

23

Fig. 8. The cumulative number of aphid days for R. padi
on oats in the monocrop and mixtures in the ex-
periments I and II in June—July. ( ) oat
monocrop, ( ) 008 mixture with 1/3beans,
(---) 088-mixture with 2/3 beans.



(plot means SE = 24.4, n = 16, two samples
with no colonies), and was not influenced sig-
nificantly by the stand type (F = 1.4 ns,
df=2,2). The numbers of A. pisum remained
low in all stand types (Table 4).

Altogether 181 bean weevils (Sitona spp.)
were trapped in the pitfall traps during 18 May

20 July. Some weevils were always caught
during the catching period, but the peak ac-
tivity occurred in early to mid June, when the
beans had 4—6 leaflets, well before flower-
ing. The relative catch was 50 % in the
monocrop, 25 % in the 088 mixture, 14 %

in the 008 mixture and 11 % in the oats
monocrop (LOGLIN, log, AG 2

= 64.4***,
df= 3).

Experiment 11. Again, R. padi was the
most abundant cereal aphid on oats. The den-
sities of S. avenae and M. dirhodum were low
(Table 3). The peak numbers of R. padi per
tiller were double those in Experiment I. The
peaks occurred before anthesis, in the first
week of July. The highest score estimates for
R. padi were obtained 2—5 July. Compari-
son of the treatment means estimated from
these values indicate that the numbers per tiller
were significantly increased by intercropping
(ln-transformation: F = 10.3*, df= 2,4). By 9

July, the densities had already decreased in the
monocrop and 008 mixture, but were still
high in the 088 mixture (ln-transformation:
F=lo.s*, df=2,4) (‘controls’ in Table 3).
Consequently, the cumulative number of
aphid-days per tiller for R. padi was signifi-
cantly higher in the mixtures than in the
monocrop (F = 10.7*, df = 2,4) (Fig. 8). Del-
tamethrin spraying significantly lowered the
R. padi densities in all stand types (ln-trans-
formation, within-factor: F =26.2**, df= 1,6)
(Table 3). The infestation of oats by frit
fly (O. frit) was negligible.

The numbers of aphids on beans remained
low (Table 4). The relatively high figure for
the mean density of A.fabae in the monocrop
is due to the presence of a single heavily-
infested stem in the sample. The decreasing
trend in the incidences of A. fabae from
monocrop to 008 mixture, similar to that in
Experiment I, was evident but not significant
(LOGLIN, logit, AG 2 = 0.3 ns, df=2). The
numbers of aphids in the sprayed plots were
negligible.

Some notching of bean leaves by Sitona sp.
weevils was observed. Mixed cropping de-
creased the relative rate of notching by 40 %

(OBB) and 55 % (OOB) (LOGLIN, logit.

Table 4. Mean numbers per plant and incidences (p =proportion of occupied stems) of A. fabae, mean numbers
ofA. pisum per plant and mean numbers ofSilona notches per leaf (most lowest leafs, Experiment II only) on field
beans on the monocrop and the mixtures.

Exp. I (1984)* A. fabae A. pisum
18 July 31 July 18 July 31 July

mean mean
mean p mean p

monocrop 148.60.29 249.00.38 2.60.3
088 mixture 45.30.10 234.30.33 2.10.1
008 mixture 48.00.09 94.50.20 4.20.0

Exp. II A. fabae A. pisum Silona sp. notches
(ii July 1985) ; ; 7 ; 7control sprayed control sprayed control sprayed

mean mean mean meanmean p mean p

monocrop 14.20.33 0.30.10 2.50.2 1.00.4
088 mixture 1.10.30 0.30.10 0.20.1 0.50.3
008 mixture 1.50.27 0 0 0.5 0 0.50.1
" no data available from sprayed plots.
OOB: 2/3 oats + 1/3 beans; 088 1/3 oats + 2/3 beans

24



AG 2 = 9.6**, df=2). Deltamethrin spraying
reduced notching by an average of 59 °/o in
all crop types (LOGLIN, logit, AG 2 = 15.6***,
df= 1) (Table 4).

Discussion

Seed yields

The experiments consisted of replacement
series in which the interspecific and in-
traspecific components of plant interactions
are confounded. Thus, no conclusions can be
drawn concerning either optimum population
densities or the relative importance of inter/
intraspecific competition. The advantage in
the biological dimension was interpreted in
terms of the land equivalent ratio, LER, which
serves to illustrate land-use efficiency in mix-
tures as compared to monocrops; it lacks ex-
planatory value.

In the very poor growing conditions late in
the season in 1984, mixed cropping with oats
was more reliable than monocropping beans,
and the yield advantage in terms of LER was
clear. As the relative yield of oats was not
decreased by mixed cropping, the net result
favoured this over monocropping. During the
normal growing season in 1985, combined
with soil of high fertility (oats in the
monocrop showed no response to an increase
in N-fertilization; unpublished results from an
adjacent experiment), mixed cropping had no
clear advantage over monocropping. The bean
yield was very poor. The results support the
finding of high variation in the yield of grain
legume, irrespective of cropping pattern, as
well as the improvement in yield stability by
mixed cropping with cereals (Varis et ai.
1982). A proper study on reliability would re-
quire a long series of experiments carried out
over several seasons. However, some degree
of confirmation was obtained for the current
recommendation of mixed cropping of field
beans with oats in Finnish conditions.

Mixed cropping increased the nitrogen con-
tent of the oat seeds as well as thebean seeds.

This finding is consistent with earlier results
on mixed cropping of oats with grain legumes.
The nitrogen content of the cereal component
rises consistently, whereas the legume compo-
nent responds more variably (Bengtsson
1973, Varis 1983, Varis et ai. 1981). In ex-
periments carried out by Melaand Paatela
(1974) with Sisu oats, the stand density perse
did not affect the nitrogen content of the
seeds. Although the influence of stand densi-
ty was not controlled in the experiments
reported here, or in the earlier Finnish reports,
it can be concluded that the increase in the
nitrogen content of oats in the legume mix-
tures is a true intercropping effect, and can
be explained by interspecific complemantari-
ty in the nitrogen uptake. In the case studied
here, the oat monocrop produced a total nitro-
gen output that was only slightly higher than
the input as fertilizer, but in the mixtures the
output/input ratio varied around 200 %.

Formation of yield

In Experiment I the seed moisture content
did not fall to acceptable levels in any of the
crop types, and did not depend on the crop-
ping pattern; the weather factors dominated
the outcome. Experiment II confirmed the
earlier findings that mixed cropping delays the
ripening of oats, and hastens the ripening of
beans (e.g. Varis 1983).

The yield component of oats which was the
most sensitive to mixed cropping was the num-
ber of panicles per plant: tillering was the
higher the lower the proportion and density
of oats in the mixture. Martin and Snaydon

(1982) obtained a similar result for barley in-
tercropped with field beans. The result sug-
gests that tillering of oats takes place before
the beans attain a competitive capacity suffi-
cient to compensate for the low total plant
density of the mixtures. Thus the response
could not be caused by interspecific interac-
tion, but simply by the lower initial plant and
biomass density in the mixtures. This expla-
nation is in accordance with the result of
Mela and Paatela (1974) in that tillering

25



sharply increases when the density of an oat
crop decreases below 300—400 plants/m 2

.

On tillers the average size of the panicles
was only ca. 2/3 of that on the main stems.
According to Mela and Paatela (1974), the
panicle size on the adventive tillers of sparse
monocrops can fall to 1/6 of those on the
main stems. In the poor growing conditions
in Experiment I, the increase in the propor-
tion of panicles produced by tillers resulted in
a decrease in the overall size of panicles, al-
though theaverage size of the panicles of the
main stems or tillers was not affected in mixed
cropping. However, in the more normal con-
ditions in Experiment 11, the increase in the
number of panicles per plant in the mixtures
was followed by an increase of overall pani-
cle size, not a decrease as predicted by the hy-
pothesis of negative correlations of the yield
components.

The reduced average panicle size, when not
compensated for by other components of the
yield, decreases the harvest index and thus the
efficiency of resource usage in yield formation
(cf. Mela and Paatela 1974). In addition to
the relative inefficiency, one disadvantage in
yielding via tillers may be a decrease in the
homogeneity of grain quality if less mature
grains with a high hull content become more
frequent. One implication of these consider-
ations is that in order both to improve the
management properties of the mixtures and
to increase the predictability of the final mix-
ture ratio, it would be beneficial to develop
oat varieties for mixed cropping with a low
susceptibility to tillering. On the other hand,
the inherited susceptibility for tillering is an
adaptative property of the small grain cereals
that allows for considerable variation in the
sowing rate and the initial seedling density
without affecting the yield.

The seed weight of a component crop usual-
ly increases as the mixture proportion de-
creases. This was true in the case of oats in-
tercropped with field beans (e.g. Varis 1983)
or with peas Pisum sativum L. (e.g. Bengts-
son 1973), but was not observed in the ex-
periments reported here. In fact, the opposite

case was indicated by an indirect measurement
in Experiment I.

The increased seed weight of field beans
caused by mixed cropping is consistent with
earlier results (Varis 1983). During the wet
and cool autumn of 1984, the relative density
of harvestable stems was also increased by
mixed cropping, and was the main reason for
the improvement in the reliability. The pod
size and the number of pods per stem were not
influenced by the cropping pattern. The
results indicate that when intercropped with
a more competitive cereal, beans respond in
a specific way that cannot be explained by the
changes in density alone. The number of pods
per stem is usually the yield component that
is most sensitive to varying density (Thomp-
son and Taylor 1977, Barry and Storey

1979, Graf and Rowland 1987), whereas pod
size is usually the component most stable in
the face of environmental variation (Dantu-
ma and Thompson 1983; see also Stoddard
1986). Pulli and Vestberg (1981) reported a
decrease in both these components as well as
in seed weight with an increase in density.

In a competitive situation (full crop), the
hypothesis of intra-plant compensation of the
temporally sequential yield components shar-
ing a common limited metabolicpool predicts
oscillatory dynamics in the number of pani-
cles or pods per plant, the number of seeds
per panicle or pod and, finally, seed weight
(Adams 1967, Adams and Grafius 1971). In
intercropping,-the negative correlations of the
yield components may not become so pro-
nounced when the intensity of interplant com-
petition is reduced. This assumption implies
that in intercropping in replacement series, the
yield components may come closer to poten-
tial levels than in the case of monocrops.

Pest incidence

The only pest species found in harmful
numbers were the bird cherry oat aphid (R.
padi), and the frit fly (O. frit) on oats. The
increase in cereal aphid numbers per tiller on
oats caused by mixed cropping was reported

26



and discussed elsewhere, as well as the slower
development of the incidence to mean ratio
of R. padi in the mixtures (Helenius 1989).

O. frit infested oats (1984 only) in equal
proportions in the monocrop and mixtures
early on during the season. In contrast, the
late adventitious tillers were more infested in
the monocrop than in the mixtures. Discus-
sion of this result would require more detailed
information about the tillering of oats in the
system studied. The results of Adesiyun

(1978) indicated that a reduction in oats stand
density can decrease the rates of colonization,
oviposition and the survival of larvae. On the
other hand, a decrease in stand density com-
bined with intercropping by the replacement
method promotes tillering and provides more
oviposition sites per plant. O. frit is very mo-
bile (e.g. Nielsen 1985), and an experiment
with field plots provides a patchy environment
where any habitat (crop type) preferences in
colonization by adults are likely to be diluted
by movement between the patches.

The incidence, but not the average colony
size, of A. fabae was decreased by mixed crop-
ping. Way and Heathcote (1966) studied the
influence of monocrop density of beans on
A. fabae: on the smaller plants in the dense
stands the mean population density per plant
was lower than that in the sparse stands, due
to a lower incidence times a lower rate of
reproduction. It is interesting, however, that
the incidence first increased with host densi-
ty, from 26 % infested plants at a density of
9.3 plants/m 2 to 34 % infested at a density
of 34 plants/m2

, and then decreased consis-
tently to 12 % infested plants at a density of
99 plants/m 2 (percentages obtained from Ta-
ble 3 in Way and Heathcote 1966). Cam-
mell and Way (1983) concluded that dense
monocrops are likely to be less severely
damaged than sparse monocrops, but that un-
dersowing or intercropping could bring about
a reduction in incidence and virus spread.
Taking the dispersive host-finding behaviour
of colonizers into account (Kennedy et al.
1959), these results support the hypothesis,
presented elsewhere in the case of R. padi

(Helenius 1989), that intercropping interferes
with secondary dispersal after alighting on the
crop, primarily via the increased distance be-
tween individual host plants. This mechanism
wouldhave the greatest effect in replacement
intercrops, where the host density is well be-
low the normal density used in monocrops.
The consequences of a decrease in the inci-
dence to damage function, even for virus
spread, are obvious.

As is the case with O. frit, the observations
on Sitona in experiments consisting of mosa-
ic crop patches should be interpreted as choice
experiments. The reduced notching of bean
leaves by Sitona weevils on the intercrop plots
confirms the finding of Baliddawa (1984).
Assuming that the activity of individuals is not
influenced by the stand type, the pitfall trap
results revealed that the decrease in notching
detected in the mixtures was proportional to
the decrease in population density in the mixed
crop patches as compared to monocrops. The
catch in the oats monocrop plots 100 m 2 in
size, bordering on the plots with beans, was
obviously due to the dispersive movements
(crawling and flying) of the weevils. The
main damage mechanism could be larval feed-
ing on root nodules, which was not measured
in this study.

Sampling for pests other than cereal aphids
was not intensive enough to give more than
indicative results. The responses of O. frit on
oats and A. fabae and Sitona spp. on beans
would merit further study.

Insecticide treatments in the mixtures

In 1984, spraying against cereal aphids had
no effect on the oat yield. The most likely ex-
planation is that both the cereal aphid num-
bers and the yield level were too low for any
damage to appear. The proportional yield
reduction caused by S. avenae is related not
only to pest numbers but also to the level of
attainable yield: it increases as the yield level
rises (Rabbinge and Coster 1984, Roermond
et al. 1986); it is realistic to assume a similar
relationship for R. padi, too. If the field beans

27



respond to the manipulation of cereal aphid
numbers via competitive interaction with oats,
then the lack of response in 1984 is as ex-
pected.

The oat yield level as well as the aphid den-
sities were higher in Experiment II than in Ex-
periment I, and spraying against cereal aphids
considerably increased the oat yield. There
were signs that the increase was higher in the
mixtures than in the monocrop and was as-
sociated with a decrease in the bean yield.
These indicative results support the hypothe-
sis of compensatory yielding in the mixtures.
However, there was also some indication that
spraying caused a decrease (although relatively
smaller) in the monocrop yield of beans, too.
One alternative explanation for the competi-
tive suppression by oats could be a relatively
stronger negative effect of spraying on the
beans in the mixtures than in the monocrop.
If pollinators were repelled by the spraying,
repellence could well be stronger in the mix-
tures with a higher leaf area and more closed
canopy than monocrops at the same time dur-
ing the season. The spraying treatments
reduced pod formation in beans, as would be
expected if pollinators were harmed; the earli-
est flowers are the least autofertile ones
(Bond and Poulsen 1983).

The deltamethrin treatments increased the
panicle density, panicle size and seed weight
of oats, equally in all stand types. It is as-
sumed here that these increases were achieved
through the virtually complete elimination of
R. padi from the treated plots. The aphid
populations peaked during the reproductive
phase (before anthesis but after the vegetative
phase). A further source-sink study would re-
veal whether an additional sink for assimilates
(aphid feeding) combined with a reduced rate
of photosynthesis (leaves covered by aphids
and honeydew) would result in similar dam-
age at this stage. It is well known that tiller
growth and survival are influenced by post
tillering conditions as a result of the priority
of the main stem in resource allocation. The
yield component most sensitive to cereal aphid
damage is usually seed weight, but with high

aphid densities even the number of grains per
panicle or ear can be reduced (Rautapää
1968, Wratten 1975, 1978, Vickerman and
Wratten 1979, Hinz and Daebeler 1980,
1982, Kuroli 1983,Kieckhefer and Kantack
1986). The possible contribution of the mild
infestationby BYDV was not evaluated in this
study.

The reduction in the nitrogen content of
oats caused by the spraying was evidently
primarily due to the increase in seed weight
and total yield (c.f. Wratten 1978, Vereij-
ken 1979, Jahn et al. 1987). The slightly
earlier maturation of the seeds, as indicated
by the reduction in the moisture content of
oats at harvest, resulting from cereal aphid
spraying could simply have been caused by a
faster depletion of resources in producing the
higher yield.

General conclusion

The mixed crop system studied here is an
example of the profitable use of intercropping
in temperate agriculture. It was demonstrated
that the process of yield formation is greatly
influenced by the choice of cropping pattern.
It was also demonstrated that each member
of the pest complex of the system is likely to
respond to intercropping in an individualistic
way that is not attributable to simple one-
to-one causalities; a realistic approach to the
study of numerical influences based on the
stages in pest population dynamics has already
been outlined by Perrin (1977).

Ideally, manipulation of pest numbers when
studying the dynamics of yield in intercrop-
ping must not lead to confounding side ef-
fects: manipulation by spraying is likely to be
a crude method in most cases. Furthermore,
because interspecific competition is a prequi-
site for compensatory yielding by a compo-
nent crop, the field experiment should include
controls for this. In a system involving com-
peting plant species and a herbivore common
to both, the interaction between competition
and herbivory may manifest itself in root
growth, above ground vegetative growth

28



and/or seed production (c.f. Bentley and
Whittaker 1979). The results supported the
view that the aspects of compensatory dynam-
ics between component crops and the change
in damage function due to management adap-
tationof the host plant should be included in
an intercropping study that attempts to evalu-
ate the effects of crop diversification on the

likelihood and nature of pest damage.

Acknowledgements. The data was compiled by Päivi
Ronni and Juha Helenius co-operatively. The manuscript
was written by Juha Helenius. The authors thank Anna-
Liisa Varis for criticism of the manuscript and John
Derome and Sevastiana Ruusamo for linguisticrevision.
The study was funded by the National Research Council
for Agriculture and Forestry and the Tiura Foundation.

References

Adams, M.W. 1967. Basis of yield component compen-
sation in crop plants with special reference to field
beans, Phaseolus vulgaris. Crop Sci. 7: 505—510.
& Grafius, J.E. 1971. Yield component compensa-
tion alternative interpretations. Crop Sci. 11:
33—35.

Adesiyun, A. 1978. Effects of seedling density and spa-
tial distribution of oat plants on colonization and de-
velopment of Oscinella frit (Diptera: Chloropidae).
J. Appi. Ecol. 15: 797—808.

Altieri, M.A. & Letourneau, D.K. 1982. Vegetation
management and biological control in agroecosystems.
Crop Protection 1: 405—430.
& Liebman, M. 1986. Insect, weed, and plant disease
management in multiple cropping systems. In: Mul-
tiple cropping systems, p. 183—218 (ed. C.A. Francis).
New York.

Baker, R.J. & Nelder, J.A. 1978. The GLIM system.
Generalized linear interactive modelling, release 3. The
Numerical Algorithms Group. Oxford.

Baliddawa, C.W. 1984. Movement and feeding activity
of adult pea leaf weevil, Sitona lineatus L. in an oat-
broadbean diculture. Insect Sei. Appi. 5: 33—39.
1985. Plant species diversity and crop pest control.

An analytical review. Insect Sei. Appi. 6: 479—487.
Barry, P. & Storey, T.S. 1979. Influence of some cul-

tural practices on the yield, development and quality
of field beans (VidafabaL.). Irish J. Agric. Res. 18:
77—88.

Bengtsson, A. 1973. Försök av samodling av ärter och
havre. Lantbr.högsk. Medd. A 200: 1—24.

Bentley, S. & Whittaker, J.B. 1979. Effects of grazing
by a chrysomelid beetle, Gastrophysa viridula, on
competition between Rumex obtusifoUus and Rumex
crispus. J. Ecol. 67: 79—90.

Bond, D.A. & Poulsen, M.H. 1983. Pollination. In: The
Faba Bean ( Vida faba L.), p. 77—101 (ed. P.D.
Hebblethwaite). London.

Cammell, M.E. & Way, M.J. 1983. Aphid pests. In: The
Faba Bean ( Vida faba L.), p. 315—346 (ed. P.D.
Hebblethweite). London.

Dantuma, G. & Thompson, R. 1983. Whole crop phys-

iology and yield components. In: The Faba Bean
(Vidafaba L.), p. 143—158 (ed. P.D. Hebblethweite).
London.

Graf, R.J. & Rowland, G.G. 1987. Effect of plant den-
sity of yield and components of yield of faba bean.
Can. J. Plant Sci. 67: I —lO.

Helenius, J. 1988. Choice of crop species assemblages as
a tool in management. An example of intercropping
oats and field beans. Ecological Bulletins, 39; 97—98.

Helenius, J. 1989. The influence of mixed intercropping
of oats with field beans on the abundance and spa-
tial distribution of cereal aphids (Horn., Aphidi-
dae). Agriculture, Ecosystems and Environment, 25:
53—73.

H inz, B. & Daebeler, F. 1980. Auswirkungen eines
Haferblattlausbefalls auf Ertrag und Qualität von
Sommergerste. Nachr.bl. Pfl.schutz DDR 34: 5—7.
& Daebeler F. 1982. Schadwirkung der Haferblatt-
laus, Rhopalosiphum padi (L.), an Sommergerste bei
geringer Befallstärke. Wiss. Z. Wilhelm-Pieck Univ.
Rostock Naturwiss. R. 31; 61—62.

Hovinen, S. 1982. Hankkijan Mikko-härkäpapu. Hank-
kijan Kasvinjal.lait. Tied. 7. 20 p.
1984. Hankkijan Ukko-härkäpapu. Hankkijan Kas-
vinjal.lait. Tied. 14. 13 p.

Jahn, 8., Merbach, W., Freier, 8., Köllner, V. & Wet-
zel, T. 1987. Untersuchungen zur Wechselwirkung
zwischen Haferlaus (Rhopalosiphum padi (L.)) und
Weizenpflanze unter Beriicksichtigung der ISN-Ver-
teilung. J. Appi. Ent. 103: 107—111.

Kennedy, J.S., Booth, C.O. & Kershaw, W.J.S. 1959.
Host finding by aphids in the field, 11. Aphis fabae
Scop, (gynoparae) and Brevicoryne brassicae L.; with
a reappraisal of the role of host-finding behaviour in
virus spread. Ann. Appi. Biol. 47: 424—444.

Kieckhefer, R.W. & Kantack, B.H. 1986. Yield losses
in spring barley caused by cereal aphids (Homoptera:
Aphididae) in South Dakota. J. Econ. Entomol. 79:
749—752.

Kuroli, G. 1983. Damage by oat aphids (Rhopalo-
siphum padi L.) in cereals. Z. Angew. Ent. 96:
463—469.

29



Litsinoer, J.A. & Moody, K. 1976. Integrated pest
management in multiple cropping systems. ASA
(American Society of Agronomy) Spec. Pubi. 27:
293—316.

Lowe, H.J.B. 1984. The assessment of populations of
the aphid Silobion avenae in field trials. J. Agric. Sci.
(UK) 102: 487—497.

Martin, M.P.L.D. & Snaydon, R. 1982. Intercropping
barley and beans. I. Effects of planting pattern. Exp.
Agric. 18: 139—148.

Mead, R. & Willey, R.W. 1980. The concept of a Land
EquivalentRatio and advantages in yield from inter-
cropping. Exp. Agric. 16: 217—228.

Mela, T. & Paatela, J. 1974. Grain yield of spring
wheat and oats as affected by population density.
Ann. Agric. Fenn. 13: 161—167.

Nielsen, L.B. 1985. Differential flight behaviour of Os-
cinella spp. (Dipt., Chloropidae). Z. Angew. Ent. 100:
392—398.

Norton, G.H. 1975. Multiple cropping and pest control.
An economic perspective. Meded. Fac. Landb.vet.
Rijksuniv. Gent 40: 219—228.

Oyejola, B.A. & Mead, R. 1982. Statistical assessment
of different ways of calculating land equivalent ra-
tios (LER). Exp. Agric. 18: 125—138.

Perrin, R.M. 1977. Pest management in multiple crop-
ping systems. Agro-Ecosystems 3: 93—118.

Pulli, S. & Vestbero, M. 1981. Genetic and manage-
ment adaptation of field bean (Vidafaba L.) in Fin-
land. J. Scient. Agric. Soc. Finland 53: 328—340.

Rabbinge, R. & Coster, G. 1984. Some effects of cereal
aphids on growth and yield of winter wheat. In: Pest
control: recent advances and future prospects (ed. P.
Bailey & D. Swincer). Proc. 4th Australian Appi. Ent.
Res. Conf., 24—28 Sept. Adelaide, Australia, p.
163—169, Adelaide.

Rao, M.R. & Willey, R.W. 1980. Evaluation of yield
stability in intercropping: studies on sorghum/pigeon
pea. Exp. Agric. 16: 105—116.

Rautapaa, J. 1968. Changes in the yield and protein
quantitiy of oat caused by Rhopalosiphumpadi (L)
(Horn., Aphididae). Ann. Agr. Fenn. 7: 95—104.

Risen, S.J., Andow, D. & Altieri, M.A. 1983. Agro-
ecosystem diversity and pest control: data, tentative
conclusions, and new research directions. Environ-
mental Ent. 12: 625—629.

Roermond, H.J.W, van, Groot, Rossing,
W.A.H. & Rabbinoe, R. 1986. Calculation of aphid
damage in winter wheat, using a simulation model.
Meded. Fac. Landb., Rijksuniv. Gent 51/3a: 1125
1130.

Ruppel, R.F. 1983. Cumulative insect days as an index
of crop protection. J. Econ. Ent. 76: 375—377.

Stoddard, F.L. 1986. Effects of irrigation, plant densi-
ty and genotype on pollination, fertilization and seed
development in spring field beans ( Vida faba L.). J.
Agric. Sci. (UK) 107; 347—355.

Thompson, R. & Taylor, H. 1977. Yield components
and cultivar sowing date and density in field beans
(Vida faba). Ann. Appi. Biol, 86: 313—320.

Tottman, D.R, & Broad, H. 1987. The decimal code for
the growth stages of cereals, with illustrations. Ann.
Appi. Biol. 110; 441—454.

Trenbath, B.R. 1976. Plant interactions in mixed crop
communities. ASA (American Society of Agronomy)
Spec. Pubi. 27: 129—169.
1977. Interactions among diverse hosts and diverse

parasites. Ann. New York Acad. Sci, 287: 124—150.
Varis, E. 1983. Härkäpavun seosviljely. In: Biologinen

typensidonta peltokasvien viljelyssä. Suomen Akate-
mian Sopimustutk. 383 Loppur. p. 149—174.

—, Hovinen, S. & Kansanen, P. 1981. Födersädens
kvalitet i trinsädesblandningar. In: Nordisk Cerealist-
förbund XXI Kongr. p. 244 —256.

—, Hovinen, S., Kansanen, P. & Kauppila, R. 1982.
Legumes in Finnish agriculture. II Nat. Symp. Biol.
Nitr. Fix. p. 219—231. Helsinki.

Vereijken, P.H. 1979. Feeding and multiplication of
three cereal aphid species and their effect on yield of
winter wheat. Agr. Res. Rep. 888. 58 pp. Pudoc,
Wageningen.

Vickerman, G.P. & Wratten, S.D. 1979. The biology
and pest status of cereal aphids (Hemiptera: Aphidi-
dae) in Europe: a review. Bull. Ent. Res. 69: 1—32.

Way, M.J. & Heathcote, G.D. 1966. Interactions of
crop density of field beans, abundance of Aphis fa-
bae Scop., virus incidence and aphid control by chem-
icals. Ann. Appi. Biol. 57: 409—423.

Willey, R.W. 1979. Intercropping its importance and
research needs. Field Crop Abstr. 32: 1—lO, 73—85.

de Wit, C.T: 1960. On competition. Versl. Landbouwk.
Onderzoek. 66.8. 82 p. Wageningen.

Wratten, S.D. 1975. The nature of the effects of the
aphids Silobion avenae and Melopolophium dirho-
dum on the growth of wheat. Ann. Appi. Biol. 79:
27—34.
1978, Effects of feeding positions of the aphids

Silobion avenue and Melopolophium dirhodum on
wheat yield and quality. Ann. Appi. Biol. 90: II—20.

Ms received March 15, 1988

30



SELOSTUS

Sadonmuodostus ja tuholaisien
esiintyminen kauran ja härkäpavun
seoskasvustoissa

Juha Helenius ja Päivi Ronni
Helsingin yliopisto. Maatalous- ja
metsäeläintieteen laitos,
00710 Helsinki

Kahdessa kenttäkokeessa vuosina 1984 ja 1985 selvi-
tettiin kauran (Puhti) ja härkäpavun (Mikko) sekavilje-
lyn vaikutusta satoisuuteen ja sadonmuodostukseen se-
kä tuholaisten runsauteen puhdaskasvustoihin verrattu-
na. Tavoitteena oli myös testata hypoteesia lajien väli-
sestä satokompensaatiosta tilanteessa, jossa tuholainen
vioittaa seoskomponenteista vain toista. Koejäsenet oli-
vat puhdaskasvustot jakorvausperiaatteen (replacement
series) mukaisesti perustetut seokset, joissa oli joko 1/3
kauraa + 2/3 papua tai 2/3 kauraa + 1/3 papua nor-
maalikylvömäärästä. Lisäksi koetekijänä oli kauran tu-
holaisen, luomikirvan Rhopalosiphum padi, vioituksen
intensiteetti, jota manipuloitiin inseklisidiruiskutuksin
(verranteet vs. ruiskutetut ruudut).

Ensimmäisessä kokeessa (1984) kasvuolot olivat epä-
edulliset etenkin loppukauden märkyydestä johtuen; li-
säksi tuomikirvojen lukumäärät kauran versoilla jäivät
suhteellisen pieniksi. Insektisidikäsittelyllä ei ollut vaiku-
tusta satoihin tai pinta-alavastaavuussuhteena(LER-in-
deksi) mitattuun seosviljelytehoon. Pavun seosviljelyte-
ho muodostui positiiviseksi, muttakauran jäi negatiivi-
seksi. Toisessa kokeessa (1985) kasvuolot suosivat kau-
raa. Ruiskuttamattomissa ruuduissa seosviljely ei kum-

maikkaan lajille ollut merkitsevästi edullisempaa tai epä-
edullisempaakuin puhdaskasvustojenviljely. Tuomikir-
van torjunta muutti seoskomponenttien kilpailusuhdet-
ta kauran eduksi; kauran seosviljelyleho kohosi positii-
viseksi (p<0.05) ja pavun seosviljelyleho laski (lähes
merkitsevä tulos, p =0.08). Tulos tukee hypoteesia, jon-
ka mukaan lajienvälinen kompensoiva satodynamiikka
on sekakasvustojen viljelyvarmuuden osatekijä.

Satokomponenttejakoskevien tulosten perusteella pää-
teltiin, että seosviljelyn vaikutuksessa kauran sadonmuo-
dostukseen määräävänä on lajinsisäinen kilpailu, kun taas
pavun sadonmuodoslus on ensisijaisesti lajienvälisen kil-
pailun säätelemää. Tämä johtopäätöstukee aikaisempia
suomalaisia tuloksia kauran vallitsevuudesta härkäpapu-
seoksissa.

Seosviljelyssä tuomikirva esiintyi kauran versoilla run-
saampanakuin kauran puhdaskasvustoissa. Papukirvan
Aphisfabae keskimääräinen koloniakoko ei seosviljelyssä
muuttunut,mutta saastuneiden versojen osuus laski. Seos-
viljely vähensi hernekärsäkkään Sitona spp. aikuisten
syöntivioitusta pavussa. Myös kahukärpäsen Oscinella frit
aiheuttaman vioituksen esiintymisessä havaittiin eroja kas-
vustotyyppien välillä.

31