|Abstract or Summary
- With the development of new selective herbicides and the frequent
change in commercial wheat cultivars, information is needed as to the
possible interaction between cultivars and herbicides. The responses
of five genotypically diverse wheat cultivars (Bezostaya, Daws, Maris
Hobbit, Stephens and Yamhill) to diuron [3-(3,4-dichloropheny1)-1,1-
dimethylurea], diclofop methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]
propanoate and 2,4-D (2,4-dichlorophenoxy acetic acid) herbicides
were compared under field and greenhouse conditions during the 1979-80
Grain yield was considered as a measure of herbicide injury when
compared to the control plots for each cultivar. Effect on components
of yield, plant height and grain protein content also were investigated.
Differences in yield performance and related agronomic characters
could be attributed to specific herbicides, designated rates and growth
stages at the time of application. The lower (1.4 kg/ha) rate of
diuron, diclofop and 2,4-D reduced yields less than the higher rate
(2.8 kg/ha). Diuron and diclofop applied at the earlier (three to to five leaf) growth stage caused greater yield reductions than when
applied at the later (five to six tiller) growth stage.
Differential yield responses were found among and within the
five winter wheat cultivars. The higher rate of diuron (2.8 kg/ha)
caused the most injury in all of the cultivars tested. Major injury
from diclofop occurred on the cultivar Maris Hobbit with minor effects
on the other four cultivars. The primary reduction in yield from
application of 2,4-D was to the cultivar Bezostaya. Among the five
wheat cultivars tested in this experiment, Daws was the most tolerant
to the three herbicides tested.
Among the yield components (number of spikes per unit area,
kernels per spike and 1000 kernel weight), number of kernels per
spike accounted for most of the variation in yield. The data showed
a direct relationship between kernel number and grain yield. Grain
protein percentage of Daws, Maris Hobbit, Stephens and Yamhill significantly
increased at the higher rate of diuron; whereas a similar
increase was noted only in Bezostaya at the lower rate of 2,4-D.
These increases in protein were associated with significant decreases
Yield reductions due to herbicide treatments were generally lower
than those due to weed competition.
Reductions in yield and corresponding changes in the other
agronomic characteristics observed in this experiment were the result
of concentrations which are higher than those normally used in
spraying wheat for weed control. This high chemical dosage was chosen
for each herbicide to assure a greater differential response among and within the wheat cultivars. It also provided information for
the plant breeder as to which cultivars had higher levels of
tolerance. Such information is important when making hybrid combinations
for the development of future varieties if higher levels
of tolerance to specific herbicides are required.