Trifluralin was evaluated at 1.1, 2.2, and 4.5 kg/ha in 1983 and 1984 at two locations in Iowa for residue carryover injury to corn the following seasons. Three methods of seedbed preparation (no-till, moldboard, and chisel plowing) for corn planting were also examined. There was no effect on corn growth at the 1.1 kg/ha rate of trifluralin. Averaged over the four experiments, reductions in corn height of 8 and 24% were observed 5 weeks after planting at 2.2 and 4.5 kg/ha, respectively. The relative degree of stunting due to trifluralin decreased as the growing season progressed. Early-season carryover injury was more severe in reduced tillage than in moldboard plow treatments in the 1983-84 Nashua experiment. Moldboard and chisel plowing reduced the concentration of trifluralin in the 0- to 7.5-cm zone of the soil profile by 62 and 31%, respectively, when compared to no-till. No yield reductions were observed at the 1.1 or 2.2 kg/ha rate of trifluralin. In 1984, grain yields were reduced by 8 and 16% at Ames and Nashua, respectively, by the 4.5 kg/ha trifluralin rate.

Simulated sprayer tank residues of the broadleaf weed herbicides dicamba, chlorsulfuron, and clopyralid applied alone and with the grass weed herbicides sethoxydim and diclofop on sunflower, tame mustard, and lentil, respectively, caused visible crop injury and reduced dry weight and yield. Dry weight production in the greenhouse and crop tolerance ratings in the field indicated that the grass weed herbicides enhanced crop injury from dicamba, chlorsulfuron, and clopyralid. Yield reductions in field experiments were also greater when dicamba and clopyralid were mixed with grass weed herbicides and applied on sunflower and lentil, respectively. This did not occur with chlorsulfuron applied to mustard. When mixed with simulated broadleaf weed herbicide residues, diclofop enhanced dry weight reductions and crop injury and reduced yield to a greater extent than sethoxydim. Crop tolerance ratings differentiated treatments and rates but were not a good estimate of the extent of yield loss. When broadleaf weed herbicides were applied at rates simulating sprayer tank residues alone or combined with grass weed herbicides, yield losses ranged up to 40% in sunflower, 70% in mustard, and 95% in lentil, compared to the untreated check.

Corn hybrids and inbreds were ranked for their relative tolerance to soil-incorporated clomazone, as assessed by the level of discoloration injury in the greenhouse. Inbred W117 was the most tolerant corn line tested. Some corn lines were affected similarly by clomazone. Inbred A619 was in the most susceptible group. Clomazone injury to A619 (susceptible) and W117 (tolerant) corn was similar when the clomazone rate was 10-fold greater on W117 than on A619. The distribution of corn lines on a sensitivity scale was of limited range; the distribution of hybrids on this scale was a single symmetrical peak. Changing the growth temperature or soil composition would change the absolute level of corn injury caused by a rate of clomazone but did not change the relative ranking of the corn lines in the test. A subset of the greenhouse-tested corn lines also was evaluated in several field locations. The tolerance of corn in a given field was highly (P<0.005) correlated with tolerance in the greenhouse; however, the absolute levels of injury differed among locations. The tolerance of- hybrids of known pedigree was highly (P<0.0002) correlated with the tolerance of the parent inbreds, indicating this trait was inherited.