Corn inbreds are often more sensitive to herbicides than hybrids. Field experiments were conducted with three corn inbreds to (1) evaluate inbred sensitivity to the acetamide herbicides acetochlor, dimethenamid, flufenacet, and metolachlor, (2) compare the effects of various crop safeners in combination with acetochlor and metolachlor, and (3) measure the effect of herbicide microencapsulation on acetochlor injury. Herbicides were applied preemergence at the registered rate and at two, three, or four times the registered rate in corn. Injury ratings, plant population, and the percentage of plants showing acetamide injury symptoms were used to measure herbicide effect. The inbreds ‘Mo17’ and ‘Great Lakes 15’ (GL15) were sensitive to acetamide injury. Reductions in plant population and increases in the injury rating and the percentage of injured plants were caused by acetochlor, dimethenamid, flufenacet, metolachlor, and flufenacet + metribuzin when applied at three times the registered rate. The inbred ‘B73’ was not injured. The safeners benoxacor and dichlormid reduced injury caused by metolachlor. The percentage of plants injured by metolachlor 15 days after treatment (DAT) was lower when benoxacor was the safener compared to dichlormid. By 28 DAT, plants treated with safeners recovered from injury, and there were no differences between the treatments. The safeners dichlormid and furilazole reduced, but did not always eliminate, injury caused by acetochlor applied at three times the registered rate. Microencapsulation of acetochlor reduced injury to GL15. When the safeners dichlormid or furilazole were included in an acetochlor formulation, microencapsulation did not further reduce corn injury.

Corn injury from isoxaflutole has been reported in sites across the corn belt, and variation in tolerance to isoxaflutole has been observed among corn hybrids. Greenhouse trials were conducted to study the variation and the inheritance of isoxaflutole tolerance in corn. Inbred lines from two families were treated with isoxaflutole applied preemergence, at four times the typical use rate, to study plant response. Plant height of corn inbreds treated with isoxaflutole compared with the untreated control ranged from 47 to 96% among eight lines within the B73 family and from 54 to 97% among six lines within the C103 family. One tolerant and one sensitive inbred line were selected from each family. The inbred lines were crossed in the field to produce four F1 hybrids. The four hybrids were treated with isoxaflutole in the greenhouse, and the tolerance of each hybrid was compared with the parent inbred lines. Data indicate that sensitivity to isoxaflutole is a heritable trait that is mediated by nuclear genes. Tolerance of corn hybrids to isoxaflutole can be predicted from the response of the parent inbreds.