Soybean Plant Damage and Yields as Affected by Metribuzin and Seed Quality1

Abstract

AbstractCrop safety is a concern when metribuzin [4‐amino‐6‐tert‐butyl‐3‐(methylthio)‐as‐triazin‐5(4H)‐one] is used as a preemergence for weed control in soybeans [Glycine max (L.) Merr.] on coarse textured soils having a low organic matter content. Six field experiments were conducted on soils that were Typic Hapludults, Typic Udifluvents, and Typic Paleudults. In each experiment three soybean cultivars were used to determine if excessive metribuzin rates interact with various seed quality factors to influence the margin of safety to soybean plants. The cultivars were ‘Bragg’, ‘Bossier’, and ‘Hampton 266A’. Seed quality factors included 1 and 2‐year‐old seed with different germination percentages, physically damaged vs. nondamaged seed, and large vs. small seed sizes. Metribuzin was applied at 0.0, 0.84, and 1.68 kg/ha to the soil surface immediately after planting.In most experiments, both metribuzin and seed quality factors affected plant damage ratings, final stands, mature plant heights, and grain yields. In seed germination and seed damage experiments, none of the seed quality ✕ metribuzin interactions were significant for any of the measured parameters. However, in the seed size experiments, metribuzin caused more plant damage and a greater reduction in final stands and heights of plants from small than from large seed, but grain yields were not affected. From a practical standpoint, this may be of little or no importance since seed size extremes in these studies probably do not occur in normal seed lots, and plant performance differences did not appear to warrant separating specific seed sizes from a given lot. Our results suggest that metribuzin ✕ seed quality interactions do not frequently result in increased plant damage, reduced stands and height of plants, and lower grain yields, but their effects are additive. Therefore, uneven stands and apparent herbicide damage symptoms may be diagnosed only as herbicide damage when actually seed quality factors may be contributing to the problem.