Field experiments were conducted to determine the influence of winter wheat seeding date and forage removal on the efficacy of cheat control herbicides, forage and grain yields, and net returns to land, overhead, risk, and management for the various cheat control strategies. Economic analysis showed that net returns were higher when wheat was seeded during the traditional seeding period (October) than when either seeded early (September) for increased forage production or delayed (November) for cultural cheat control. Some herbicides were economically beneficial at two of three locations where the initial cheat population exceeded 170 plants/m2.

Root absorption of subtoxic levels of metribuzin and its ethylthio analog (ethyl-metribuzin) by downy brome, jointed goatgrass, and winter wheat increased by a factor of three to five times as temperature increased from 10 to 20 C. Absorption of ethyl-metribuzin per gram dry weight was similar for all three species. Absorption and distribution of ethyl-metribuzin, but not metribuzin, were similar per gram dry weight in downy brome and jointed goatgrass. Absorption of metribuzin per gram dry weight was lower for winter wheat than for the other two species at 20 C. In general, the ratio of absorbed ethyl-metribuzin detected in shoots to that in roots was less in winter wheat and jointed goatgrass than in downy brome. The absorption by roots of 14C-herbicides relative to water was similar for winter wheat and jointed goatgrass. Absorption of both 14C-herbicides by winter wheat and jointed goatgrass was nonpreferential with respect to water absorption at 10 and 15 C. However, at 20 C 14C-herbicide absorption was reduced 5 to 30% with respect to water absorption. Downy brome absorption of 14C-herbicides with respect to water was 30 to 50% less than that of the other two species.

Our objective was to identify traits in winter wheat important to competitiveness against jointed goatgrass, measured as increased wheat yields and reduced jointed goatgrass seed production. Jointed goatgrass is an important winter annual grass weed that cannot be controlled selectively in winter wheat. Seven cultivars of soft white winter wheat were grown with and without competition from jointed goatgrass over two growing seasons. Measurements of numerous traits of winter wheat and jointed goatgrass were recorded throughout each growing season. The data were analyzed using path analysis with latent variables to determine which traits most enhanced competitiveness. In a drier year, increased rate of height development was important in maintaining wheat yields when wheat was growing in competition with jointed goatgrass. Increased rate of height development also was an important trait in reducing jointed goatgrass seed production. In a wet year compared to a dry year, the number of wheat heads per plant, the rate of water use, and weight gain were positively correlated to maintaining winter wheat yields. Jointed goatgrass seed production in the wet year was reduced overall compared to the dry year, but from the cultivars tested, there were no traits identified that were critical in enhancing this loss of seed production. This study suggests that cultivars with greater height development rates will be more competitive when growing in fields infested with jointed goatgrass.

Inhibition of net photosynthesis of jointed goatgrass and downy brome protoplasts by metribuzin and its ethylthio analog (ethyl-metribuzin) was greater at 25 than at 10 C. As temperature increased from 10 to 25 C, the concentration of ethyl-metribuzin required to inhibit net photosynthesis 50% (I50) decreased by a factor of 3.5 and 4.3, respectively, in jointed goatgrass and downy brome. I50 values for metribuzin decreased by a factor of 1.5 and 2.5 in jointed goatgrass and downy brome, respectively, for the same 15 C increase in temperature. Based on I50 values at 10 C, metribuzin was nine times more inhibitory than ethyl-metribuzin in jointed goatgrass and eight times more inhibitory in downy brome. At 25 C, metribuzin was only 4.7 and 3.9 times more inhibitory than ethyl-metribuzin in jointed goatgrass and downy brome, respectively. Thus, cold temperatures reduced the activity of ethyl-metribuzin more than metribuzin. The activity of both herbicides was reduced less in protoplasts of jointed goatgrass than in protoplasts of downy brome over the 15 C range.