a1 Graduate Research Assistant, Department of Horticulture, Iowa State University, Ames, IA 50011.
a2 Professor, Department of Horticulture, Iowa State University, Ames, IA 50011.
Weeds are considered the most important pest group for farmers interested in lowering external inputs and avoiding synthetic chemical use. Corn gluten meal (CGM) is a natural preemergence weed control used in turfgrass, which reduces germination of many broadleaf and grass weeds. The objective of this study was to investigate weed cover and vegetable seedling survival in field plots when CGM is incorporated before planting. Three studies were conducted, with three replications for each study. Five rates of powdered CGM (0,100, 200, 300, and 400 g m–2) were weighed and incorporated into the top 5–8 cm of soil in recently disked 1.5-m by 2.7-m plots. Seeds of eight vegetables were each planted in rows 1.4 m long and 0.3 m apart. Seedling survival and percentage of weed cover were recorded for each plot. Corn gluten meal at rates of 100, 200, 300, and 400 g m–2 reduced mean weed cover by 50, 74, 84, and 82%, respectively, compared with the control. Seedling survival at 100 g CGM per m2 was reduced by 67% for ‘Comanche’ onion, 35% for ‘Ruby Queen’ beet, 41% for ‘Red Baron’ radish, 71% for ‘Provider’ bean, 73% for ‘Scarlet Nantes’ carrot, 59% for ‘Maestro’ pea, and 68% for ‘Black Seeded Simpson’ lettuce, compared with the control. Seedling survival for ‘Daybreak’ sweet corn was not reduced by rates of 100 or 200 g CGM per m2, but was reduced by 26% at a rate of 300 g CGM per m2 compared with the control. Because of the reduction in seedling survival at even the lowest rate of CGM (100 g m–2), direct seeding of these vegetables into soil into which CGM has been incorporated is not advisable. Using transplants may be an alternative that takes advantage of the herbicidal effects of CGM and the nitrogen it provides.