Agriculture Reference
In-Depth Information
Figure 3.3
Cabbage seedpod weevil larvae damage of canola seeds.
2000
1500
1000
500
0
B. napus
B. rapa
B. juncea
S. alba
Species
No control
Partial control
Full control
Figure 3.4
Seed yield (t ha
−
1
) from four
Brassicaceae
species as affected by late-season insect infestation when grown with
full insect control, partial insect control and no insect control.
1993. Forty genotypes were grown in a pseudo-split-
plot design where each entry was grown under three
treatments: full weevil control with several insecticides,
partial control with one insecticide, and no chemical
control of the pest (Figure 3.4). The results differed
between the four species investigated. However, with-
out chemical control three of the four species showed
yield reductions (some to a large degree). It is also obvi-
ous that
Sinapis alba
has more insect resistance (or
tolerance) than the other species and indeed offered
breeders a source of resistance through intergeneric
hybridization (see later). Additional data regarding
cost of chemical application etc. can then be used in
co-ordination with these data to estimate the actual
economic effect of this pest on
Brassica
crop production.
A major difficulty in carrying out effective disease
impact trials is to remove variation in as many other
factors which may interact with those which are under
study, as possible. For example, if the effect of a par-
ticular air-borne fungus is to be studied, then attempts
