Stand Establishment and Yield of Corn as Affected by Herbicides and Seed Vigor

Seed quality and herbicide injury are factors that might interact to affect corn {Zea mays L.) yields. Field studies were conducted to determine if corn grown from low-quality seed was more susceptible to herbicide injury than corn grown from high-quality seed. Seed lots with standard warm germinations above 90% but cold test germinations ranging from 50 to 96% were obtained for three U.S. Corn Belt hybrids. Herbicide treatments of cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl) acetamide], and EPTC⁺ [S-ethyl dipropylthiocarbamate plus R-25788 (N,N-diallyl-2,2-dichloroacetamide)] were preplant incorporated at rates ranging from one to three tunes those normally used for soil types common to these experiments. The soils were Drummer silty clay loam (Typic Haplaquoll) and Flanagan silt loam (Aquic Arguidoll). Seed quality, hybrid, and seedbed environment all interacted to affect emergence, herbicide injury, stand density at harvest, and grain yield. Seedlings from seed lower in vigor received greater herbicide injury in two of the five seedbed environments investigated, but this interaction was not significant for percent seedling emergence, plant density at maturity, and grain yield. Some herbicide treatments caused grain yield reductions of 4 to 13% but were limited to above-normal rates of cyanazine and EPTC⁺ and were not associated with plant death. Visual symptoms of herbicide injury on seedlings were usually out-grown with no resultant effect on grain yield. Grain yield reductions of up to 32% occurred from seed low in cold test germination. Yield reductions from low quality seed did not occur with all hybrids or in all seedbeds, but when yield reductions did occur, they were associated with decreases in plant density. We conclude that any interaction of corn seed quality with herbicides applied at recommended rates is minor compared with effects of poor seed quality per se, unwarranted high herbicide rates, hybrid differences, or limited soil moisture.