- Equipment for strip-till planting is under development in wheat-fallow
rotations in the Columbia Basin of Oregon. This involves the
absence of tillage during the fallow season. At planting time, the
strip-till planter creates a narrow band into which the wheat seed is
placed. The area between the rows is undisturbed except for the
deposition of a 2-cm thick layer of soil displaced from the tilled
area. Chemical weed control is required between the rows. Preliminary work has shown that metribuzin [4-amino-6-tert-butyl-3-
(methylthio)-as-triazin-5(4H)-one] is a promising herbicide for this
purpose. Factors influencing the application, effectiveness, and
selectivity of metribuzin used in conjunction with strip-till planting
were investigated in the laboratory and greenhouse.
Application of metribuzin in combination with liquid fertilizer
would be convenient and economical. Laboratory experiments were conducted to determine the physical compatibility of four liquid fertilizers: Solution 32 at 56 kg N/ha, 10-34-0 at 45 kg P₂0₅/ha,
0-0-15 at 22 kg K/ha, and 11-0-0-26 at 22 kg S/ha, with three metribuzin formulations each of Sencor and Lexone at 112 g a.i./ha.
Wettable powder, flowable, and dispersible granule formulations
of both Sencor and Lexone were tested. Only the wettable powder
formulations were sufficiently compatible with the liquid fertilizers
tested to be recommended for practical commercial use. Large
differences were seen between the other formulations. Their use with
liquid fertilizers might require the addition of compatibility agents
or mixing them with water first, before adding them to the fertilizers. When compatibility is obtained after mixing them with water
first, continuous agitation might be required to maintain the suspension. No major differences were observed between comparable formula
tions of Sencor and Lexone.
Greenhouse experiments were conducted to determine the biological compatibility of Solution 32 and metribuzin on downy brome (Bromus
teetorum LJ, the effect of Solution 32 on downy brome and wheat
emergence, the effect of soil layer on metribuzin effectiveness for
downy brome control, and the effect of banding width over the wheat
row and wheat seeding depth on metribuzin phytotoxicity to wheat.
More effective downy brome control was obtained when metribuzin
was mixed with Solution 32 than when it was used alone. Solution 32
was used at 0, 36, 54, and 79 kg N/ha, and metribuzin at 0, 14, 28,
56, and 112 g a.i./ha. Solution 32 itself had some phytotoxic
effects on downy brome at the high rates. Wheat was not affected as
severely as downy brome. Application of metribuzin to the surface of the newly deposited
soil layer was more effective in controlling downy brome than when
the herbicide was applied and then covered with the soil layer. Results suggested that better downy brome control could be obtained
with metribuzin applied after the strip-tiller had deposited the soil
layer between the rows, especially if adequate rainfall is expected.
Under such rainfall conditions, metribuzin covered with a soil layer
may leach deeper out of the root zone and less effectiveness could
Both seeding depth of wheat and width of the unsprayed area were
factors influencing metribuzin phytotoxicity to wheat. Greater wheat
injury was observed when the herbicide was applied on top of, or too
close to, the seed row, particularly when wheat was planted shallow.
The results suggested that wheat should be planted 3 cm deep or
deeper when the unsprayed band is 15 cm wide, and at least 5 cm deep
when the unsprayed band is 10 cm wide.