Impact of Corn Gluten Meal Applications on Spring-Transplanted Onion Injury and Yields

Abstract

Research to determine the relative benefits among alternative herbicides for weed control in onions (Allium cepa L.) should focus on weed control efficacy, and the impact of herbicides on crop injury, and the resulting weed competition on crop yields. Herbicide injury and weed competition can produce disproportionate reductions in onion yields as a result of onion's slow growth rate, short height, non-branching plant structure, low leaf area, and shallow root system. Field research was conducted in 2002 and 2003 in southeast Oklahoma (Lane, OK) to determine crop safety and yield response of selected pre-emergent synthetic herbicides and corn gluten meal (CGM) on spring-transplanted onion, cv. Hybrid Yellow Granex PRR, production. There were 21 treatments [12 synthetic herbicide treatments, five CGM applications, a full-season weed-free (hand-weeded) treatment, a full-season weedy-check, a partial-season weed-free (weed-free for the first half of the growing season by handweeding, then the weeds were allowed to grow), and a weedy-check without onions]. Synthetic herbicide treatments included pendimethalin applications at 0.5, 1.0, and 1.5 kg·ha−1 ai, oxyfluorfen at 0.1, 0.2, and 0.3 kg·ha−1 ai, and also tank-mixed at these three levels. In addition, the highest rate of each herbi-cide-pendimethalin (1.5 kg·ha−1 ai), oxyfluorfen (0.3 kg·ha−1 ai), and the tank mix of pendimethalin (1.5 kg·ha−1 ai) plus oxyfluorfen (0.3 kg·ha−1 ai)-were applied and kept weed-free by hand to determine the crop safety of these herbicides. CGM was applied at 1,000,2,000,3,000, and 4,000 kg·ha−1. A weed-free (hand-weeded) treatment was also combined with the highest CGM rate (4,000 kg·ha−1) to determine the effect of the CGM on crop injury and growth. Visual crop injury ratings were collected at 3, 5, 10, 20, and 30 days after planting, along with yields of marketable bulbs segregated by size. No phytotoxic symptoms or yield reductions were observed due to the synthetic herbicides or CGM applications. These compounds provided sufficient crop safety when applied at the rates studied. Increased weed competition caused a shift in bulb size distribution across the four bulb categories (colossal, large, medium, and small), resulting in a decreased number of colossal and large bulbs and an increase in small bulbs. Although the synthetic herbicides and CGM provided crop safety, and to some extent early weed control, reductions in crop yields as a result of weed competition demonstrated the need to include supplemental weed control with post-emergence herbicides or other weed control methods to produce maximum onion yields.