Split application of herbicides for wild oat control may minimize wild oat competition with wheat while reducing the number of wild oat seeds returned to the soil. Field experiments were conducted in 2000 and 2001 to evaluate the effects of CGA-184927, fenoxaprop-P, flucarbazone, and ICIA 0604 at labeled and reduced rates on wild oat control, wild oat seed rain, and wheat yield. Each herbicide was applied once at 25, 33, and 100% of the labeled rate at the two-leaf stage of wild oat or split applied at 50 and 66% of the full rate as two equal applications. Excellent full-season wild oat control was obtained with CGA-184927, flucarbazone, and ICIA 0604 applied twice at reduced rates. ICIA 0604 or CGA-184927 split applied at 25 and 33% rates (totaled 50 and 66% of the full rate) provided wild oat control equal to one application of labeled rates. Wild oat seed rain was similar among all herbicide treatments, except plots treated with fenoxaprop-P once at 25 and 33% rates where seed rain was higher and equal to 47% of untreated plots. Wheat yields and net returns were highest and similar after treatment with CGA-184927 or ICIA 0604 applied either once at the labeled rate or split applied at 25 or 33% rates.

A bioassay, based on seedling shoot inhibition with difenzoquat at 10 mg/L, provides a rapid means of predicting hard red spring wheat (HRSW) cultivar response to foliar-applied difenzoquat. The tolerance of several cultivars to difenzoquat was determined by shoot length inhibition in the laboratory, and by visible crop injury and shoot dry weight in the greenhouse. Of the 19 cultivars tested, one cultivar that was susceptible in the laboratory assay was intermediate in tolerance to difenzoquat in the greenhouse assay; two cultivars that were tolerant in the laboratory bioassay were of intermediate tolerance in the greenhouse assay. Results from laboratory and greenhouse studies both identified cultivars distinctly susceptible to difenzoquat. Shoot inhibition indicated that HRSW cultivar susceptibility to difenzoquat involves continuous variation from tolerant to susceptible. This may explain why some cultivars show differential responses to difenzoquat under different environmental conditions.

Perron's test, Johansen cointegration analysis, and a vector error-correction (VEC) model are used to identify structural change, as well as to examine price dynamics in the U. S. and Canadian hard red spring (HRS) and durum wheat markets. It is found that, due to the U. S. Export Enhancement Program (EEP), price instability experienced in June 1986 has resulted in structural changes for Canadian HRS and durum prices. We also find that Canadian prices have significant effects on the determination of the U. S. prices in the North American wheat market.