Field experiments were conducted at two locations in Georgia to evaluate wild radish control and soft red winter wheat tolerance of herbicides applied February 1 (one- to five-tiller stage) or March 1 (three- to seven-tiller stage). Bromoxynil controlled wild radish with no wheat grain or forage yield reductions in any experiment. Thiameturon controlled wild radish when applied at rates >0.02 kg/ha on March 1. Metribuzin, dimethylamine salt of 2,4-D, and dimethylamine salt of MCPA provided late-season control of wild radish. February 1 treatments of metribuzin reduced wheat stands at Plains. The difference was attributed to environmental conditions, wheat tiller number at application, and possibly to differences in soil fertility at planting. Metribuzin, thiameturon, dimethylamine salt of dicamba, MCPA, and 2,4-D reduced wheat forage yield at Tifton. Dicamba did not control wild radish and reduced grain yield when applied at a rate of 0.3 kg ai/ha on March 1.

When applied correctly, atrazine can be used safely in certain areas of the United States for weed control in winter wheat, but persistence in the soil may injure wheat replanted after crop failure. Studies were conducted at Moro, OR, in 1989–90 and 1990–91 to determine the effect of September preplant applications of atrazine at 0.56, 1.12, and 2.24 kg a.i. ha-1 (1X, 2X, and 4X label rates) on wheat seeded at that time and on wheat re-seeded 2 or 6 mo later. Yield of winter wheat re-seeded in November following September atrazine applications was not reduced at any rate. The September-planted wheat was killed with glyphosate in the spring to simulate winter killing, then plots were re-seeded to spring wheat. The commercial rate of atrazine, 0.56 kg ha-1, caused only minor injury to spring wheat, but injury at the 2X and 4X rates was excessive.

Sixteen field experiments were conducted across Oklahoma to evaluate the effects of MON 37500 time of application on cheat control, and winter wheat injury and yield. Winter wheat injury from MON 37500 applied preemergence (PRE) was slight and was influenced by cumulative precipitation for 10 d after application. Winter wheat injury was more frequent with early vs. late postemergence (POST) applications and was influenced by wheat growth stage and mean, high, and low air temperatures before and after application. Cheat control averaged 75% (n = 16 treatments with four to six replicates) when applied PRE and 88% (n = 126 treatments with four to six replicates) when applied POST. Cheat control from MON 37500 applied POST declined with increasing cheat growth stage at application and with decreasing mean diurnal low temperatures 0 to 14 d and 0 to 21 d before application. MON 37500 applied PRE increased yields 52 and 66% compared with the untreated control in Year 1 and Year 2, averaged over eight experiments each year. MON 37500 applied POST increased wheat yields 68 to 69% compared with the untreated check in Year 1 and Year 2, when averaged over all applications in eight experiments each year. Wheat yields were greater from fall POST applications than from late-winter applications.

Field studies were conducted to evaluate the tolerance of Italian ryegrass and the metribuzin-sensitive winter wheat cultivar Dozier to metribuzin, chlorsulfuron, flufenacet plus metribuzin, chlorsulfuron plus metsulfuron, diclofop, and combinations of these herbicides applied preemergence (PRE) and postemergence (POST) to wheat in the two- to three-leaf (2–3 LF) at Feekes' stage 1 and to one to two tiller wheat (TILL) at Feekes' stage 3. Italian ryegrass control was 80% or greater with diclofop at all rates and application timings; flufenacet plus metribuzin PRE at all rates; metribuzin POST at 2–3 LF at all rates; and chlorsulfuron or chlorsulfuron plus metsulfuron PRE followed by (fb) metribuzin POST at 2–3 LF. Control of 2–3 LF Italian ryegrass was inconsistent with flufenacet plus metribuzin, chlorsulfuron, and chlorsulfuron plus metsulfuron. Italian ryegrass control was poor with flufenacet plus metribuzin TILL, metribuzin PRE, and metribuzin TILL. Metribuzin applied alone and after chlorsulfuron or chlorsulfuron plus metsulfuron injured wheat. Wheat recovered from flufenacet plus metribuzin injury. However, injury from metribuzin at 280 g ai/ha PRE, 2–3 LF, and at 420 g/ha, 2–3 LF, resulted in season-long injury. Yields were significantly reduced because of metribuzin (PRE, 2–3 LF, or TILL) injury and also by chlorsulfuron or chlorsulfuron plus metsulfuron (PRE) fb metribuzin (2–3 LF).