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Herbicide Applications in Tillered Winter Wheat for Doublecrop Soybean Weed Control¹

M. J. McHarry and George Kaputa²

Effective, doublecrop soybean [Glycine max (L.) Merr.] weed control usually requires a foliar-active herbicide to control emerged weeds and one or two residual herbicides to control those that emerge after planting. This combination is expensive in relation to the narrow profit margin frequently experienced. If timely rainfall does not occur shortly after application, poor weed control may occur, resulting in reduced soybean yields. Field studies were conducted on a Weir silt loam (fine, montmorillinic, mesic Typic Ochraqualfs) to evaluate alternative methods of herbicidal weed control in doublecrop soybeans.

Oryzalin (3,5-dinitro-N⁴, N⁴-dipropylsulfanilamide) and USB 3153 (N³,N³-di-N-propyl-2,4-dinitro-6-trifluoromethyl-M-phenylenediamine) applied after the winter wheat (Triticum aestivum L.) was fully tillered but prior to the jointing stage (full-tiller) did not cause any visual injury or yield reduction any of the 3 years of the study. Oryzalin at 2.8 kg/ha in 1976 and at 1.68 kg/ha in 1977 and 1978 controlled at least 85% of all weeds and volunteer wheat in the doublecrop soybeans that followed the wheat harvest. USB 3153 applied at 1.12 kg/ha hi 1977 controlled more than 85% of the large crabgrass [Digitaria sanguinalis (L.) Scop.], ivyleaf morningglory (Ipomoea hederacea), and Pennsylvania smartweed (Polygonum pennsylvanicum L.) but common ragweed (Ambrosia artemisiifolia L.) and volunteer wheat control was not acceptable (<80%). In 1978, USB 3153 at 0.84 and 1.12 kg/ha controlled 95% or more of all weeds and volunteer wheat. Herbicides applied after doublecrop soybean planting provided acceptable weed control in 1976 and 1977 but poor control in 1978. These results indicate that oryzalin and USB 3153 applied over-the-top of tillered wheat provide good weed control in doublecrop soybeans and do not affect wheat yields at rates needed for acceptable weed control. Similar studies are needed at other locations to fully evaluate these treatments under different soil and environmental conditions.

Key Words: Full-tiller stage • Foliar-active herbicide • Grass and broadleaf weeds • Over-the-top application • Volunteer wheat

² Graduate research assistant and associate professor.

Received for publication March 12, 1979.