Volunteer Legume Control in Legume Seed Crops with Carbon Bands and Herbicides. I. White Clover1

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Abstract
In legume seed production, volunteer legumes from seed in the soil may result in contamination of seed lots. No herbicides are available which can selectively control volunteer legumes in seeded legumes when both are exposed to the herbicide. Greenhouse and field experiments on white clover (Trifolium repens L.) were conducted in western Oregon to determine the potential of using activated carbon applied in bands over the seed row, with nonselective herbicides, to selectively control volunteer legumes. A 25‐mm band of activated carbon was applied to the soil surface over the seeded row during planting and a nonselective herbicide was applied broadcast immediately. Weed control was visually evaluated, and stand and seed yield of the white clover was measured. The carbon: herbicide ratios required for protection with 0.5 kg/ha of diuron [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea], atrazine [2‐chloro 4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine], and simazine [2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine] were 50:1, 200:1, and 200:1, respectively. This reduction resulted in seed yields of 80, 40, and 14% of the check at first harvest of fall‐planted white clover. Atrazine and simazine at 1.25 and 1.5 kg/ha, respectively, reduced seedling numbers to the same extent as diuron at 2 kg/ha. In the second harvest of these treatments, seed yields from plots established with diuron at 2 and 3 kg/ha were similar to those from the check plots. Seed yields from white clover established with carbon bands in the spring were not reduced by diuron. White clover injury was greatest when diuron was applied to soil that was wet on the surface. Seed germination and seed weight were not influenced by the herbicides used in these experiments. Weed control between the carbon bands was good but grasses and broadleaf weeds also were protected by the carbon band. With carbon banding, volunteer white clover and volunteer narrow birdsfoot trefoil (Lotus tenuis Waldst. & Kit) were both reduced 95% by diuron applied at 2 and 3.3 kg/ha. Individual circumstance will determine whether the increase in seed lot quality that results from the control of volunteer legumes will offset the reduction in the quantity of seed produced.

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