The cucumber (Cucumis sativus L.) accession PI 390244 tolerated up to 0.56 kg/ha atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] whereas most cultivars and accessions were killed by 0.14 kg/ha. The possible mechanisms for tolerance were investigated by comparing growth rates, effects on photosystem II in isolated chloroplasts, and differences in uptake and translocation of 14C-atrazine between tolerant PI 390244 and the susceptible cultivar Marketmore 70. PI 390244 had significantly more leaf area than Marketmore 70, but less root biomass. Isolated chloroplast preparations from both cultivars were equally susceptible to the herbicide. Although PI 390244 absorbed more total 14C-atrazine, it translocated less radioactivity from the roots. While the concentration of 14C found in the PI 390244 roots was 10 to 30% greater than in Marketmore 70, the amount of radioactivity in the cotyledons, and first and second true leaves of Marketmore 70 were 53, 34, and 55% higher, respectively, after 48 h.

Weed-control evaluations in ratoon-cropped grain sorghum [Sorghum bicolor (L.) Moench.] indicated that acceptable broadleaf weed control (>80%) in the second crop could be achieved by the use of a contact herbicide plus a residual herbicide applied after first harvest. Annual grasses, especially volunteer grain sorghum, were controlled in the second crop with metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] plus propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] applied preemergence at planting and followed by metolachlor, cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] applied after first harvest. Second-crop grain yields were not adversely affected by any treatments, and it appeared that satisfactory weed control in the first crop lessened the need for a residual herbicide in the second crop.

Glyphosate was compared with other commonly used corn herbicides at three locations in Kentucky in 1998 and 1999. Sequential glyphosate treatments provided greater than 87% control of common cocklebur, ivyleaf morningglory, common lambsquarters, and giant ragweed. Control of these species with glyphosate treatments was similar to the control with atrazine plus other postemergence (POST) herbicides. Generally, treatments containing s-triazines and chloracetamides applied to the soil surface were not as effective as sequential glyphosate or atrazine plus POST herbicides. Corn yield was not significantly different at any location or for any year, whereas differences in net return occurred at one location in 1998.