Vol. 16—1962 - NorthEastern Weed Science Society

DISCUSSION
One Year After Application (1959):
395
Observations one year after treatment showed a high degree of
weed control but some weeds, broadleaves in particular, were present
in many of the plots. There was regrowth of some grasses
such as sandbur and crabgrass (shallow roots), and of broadleaf
species such a Linaria, Stellaris, Lepidium and Chenopodium within
the plots at the lower two rates. Living plants of equisetum
were found in both the diuron and simazine plots, except at the
two higher rates.
I
Eliminating the two higher rates in which weed control was
so complete as to show no differences, the data shows diuron t¢
be appreciably more effective than simazine on grasses, and equal
to or slightly more effective than simazine against broadleaf
weeds (Table II). In fact, on grasses, 10 pounds of diuron usually
performed as well as 16 pounds of simazine (Tables II and IV).
Thus, these tests indicate that the first year diuron gives more
effective weed control than simazine on an equal active ingredient
basis. As the rate of application increases above the minimum
required for complete kill, differences in the materials are not
evident.
This difference in efficiency between the two compounds must
be taken into account in evaluating the data on surface washing
on slopes. As can be seen from the data, the effect of down-Slope
washing was not appreciably different·, between the two compouncll.s
at equal lower rates. (Table III) Both materials tended to wash,
as would be expected. At equal higher rates, the effect of diuron
was more pronounced, but Whether this was due to a greater ten~
dency to wash, or to its greater herbicidal efficiency, is not
clear from these data.
Second Year After Application (1960):
Observations the second year after application (Table VI)
showed 50 to 60 per cent vegetation control in the plots at the
10 pounds per acre rate of both materials; 60 to 80 per cent c~ntrol
at the 16 pounds per acre rates; but 80