Field experiments were established to evaluate the effect of herbicide treatments on control of tall fescue before spring or fall no-till alfalfa planting and to determine the effect of fescue control on alfalfa seedling establishment, forage yield, and forage quality. No treatment provided significantly greater tall fescue control than the standard two applications of paraquat at 13- to 21-day intervals. Fescue control values with this treatment ranged from 86 to 99% over experiments and were associated with maximum values for alfalfa ground-cover and alfalfa yield percentage parameters, 52 to 83% and 64 to 96%, respectively. Glyphosate and SC-0224 at 2.2 kg/ha and greater generally gave tall fescue control equivalent to the paraquat treatment in both spring and fall seedings as did sethoxydim at 0.6 kg/ha in spring seedings. Applications of fluazifop or HOE-0661 did not result in satisfactory tall fescue control or alfalfa establishment. Adding nonionic surfactant to glyphosate or SC-0224 did not increase tall fescue control. There was a direct linear relationship between tall fescue control and both alfalfa seedling establishment and yield percentage.

In full-season soybean experiments, adding glyphosate, paraquat, or HOE-0661 to chlorimuron, chlorimuron plus linuron, chlorimuron plus metribuzin, or imazaquin was required for effective weed control, especially eastern black nightshade. In double-crop soybean experiments, chlorimuron plus linuron provided similar weed control and yields with or without either glyphosate, paraquat, or HOE-0661. In both full-season and double-crop soybeans, metolachlor combined with chlorimuron mixtures did not enhance weed control or increase yield. These studies indicate a potential for reducing the use of nonselective herbicides or metolachlor when chlorimuron or imazaquin are components of tank mixes, particularly in double-crop no-till soybeans.

Experiments were conducted in 1988 and 1989 at four sites in Virginia to test weed control efficacy in double-crop, no-till soybean production systems with reduced rates of nonselective herbicides. Chlorimuron plus linuron at 0.04 plus 0.46 kg ha-1 gave more than 94% control of five weed species, but only 81 to 86% control of three weed species. Tank mix additions of reduced rates of either glyphosate, HOE-0661 or paraquat to the chlorimuron plus linuron treatment increased large crabgrass and common ragweed control.