- In previous research, bromacil gave good performance when
it was applied in early fall with fairly dry soil conditions and before
the fall germinating weeds had started growth. On the other hand,
if bromacil was applied in late November, December, or January
on nearly saturated soil with weeds that had grown for one or two
months, weed control was quite noticeably reduced. Field and
greenhouse studies were conducted at Corvallis, Oregon, to determine the influence of soil moisture and time of herbicide application on bromacil movement and performance.
In one field trial, two or six acre-inches of water were applied
by sprinkler irrigation at intervals following herbicide treatment. Intervals used were one day, two, four, or eight weeks following herbicide application on dry soil. Field bioassay with rape, wheat, oats,
annual bluegrass, sugar beets, and winter field peas indicated that
the performance of bromacil applied to dry soil was not affected by differences in irrigation levels or by the time interval between
application and irrigation. Bioassay of core segments taken from
the top six inches of soil showed no difference due to treatment
and indicated that bromacil was not leached below three inches
regardless of irrigation treatment. Of the bromacil found in the
top three inches, approximately half of it was in the 0-1 inch segment.
Difficulty in duplicating fall conditions appeared to have a
definite effect on results of field studies. Extensive loss of soil
moisture due to evaporation was probably the main factor causing
deviation from the desired conditions.
Another field trial included 0-, 1.5-, 3-, and 6-inch sprinkler
irrigation rates on an annual bluegrass stand which had been treated
with either pre- or post-emergence applications of bromacil. Irrigations were applied immediately after the post-emergence treatment. Both pre- and post-emergence applications of bromacil gave
good control of annual bluegrass regardless of subsequent post-emergence
irrigation. However, total precipitation during the first
month was only 0.25 inches and where there was no irrigation,
bromacil did not give adequate control.
Greenhouse leaching studies with soil columns did not give
satisfactory results. Consistent patterns of leaching throughout
replications could not be accomplished. When bromacil movement was determined by the use of soil columns and subirrigation with 1.5
inches of water, there was no difference in movement whether it was
applied to water-saturated or dry soil. A preliminary experiment
with a shorter subirrigation period, however, resulted in less
movement of the bromacil applied to dry soil.
Bromacil movement in soil by subirrigation is not the same
as leaching downward. Water moving through soil from subirrigation occurs through all except the very large pores; whereas in
downward leaching, water primarily moves by gravity through the
large pores once the small pores are filled.