Evaluation of herbicide-resistant soybean response to heat stress and weed management systems

Weed management studies were conducted in soybean to compare treatments within three herbicide-resistant varieties and a conventional variety system with an accompanying greenhouse based dose response analysis of glyphosate and glufosinate on sicklepod and Texas panicum. Each variety had four treatments: (a) PRE, (b) grass PRE followed by one appropriate POST, (c) broadleaf PRE followed by one appropriate POST, and (d) appropriate POST only herbicide applications. Treatments using glyphosate and glufosinate provided the same or a higher level of weed control compared to a PRE only treatment within each system. Yield was highest with treatments using glyphosate and glufosinate compared to a PRE only treatment within each system. The dose response analysis showed that glyphosate controlled Texas panicum better than glufosinate and glufosinate controlled sicklepod better than glyphosate. Field and greenhouse studies were conducted to compare agronomic and physiological characteristics of selected herbicide-resistant and conventional soybean (Glycine max) varieties. Under conditions of heat stress, glyphosate-resistant varieties did not perform as well as conventional varieties of soybeans. Under heat stress conditions glyphosate-resistant soybean not only produced lower yields, but they also suffered from elevated levels of stem splitting.