In a 2-yr field study with preplanting-soil-incorporated treatments of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], tolerance of soybeans [Glycine max (L.) Merr.] to these herbicides, as measured by seed yield, was increased by increasing the seeding rate one-and-one-half or two times that normally recommended. These results agree with suggestions in the literature that plants can compete for herbicide in the soil, and suggest that increased seeding rates of soybeans can partially reduce the adverse effects of atrazine carryover or excessive metribuzin application.

Field experiments were conducted over a 4-yr period to determine the influence of selected herbicides on ozone injury in tobacco (Nicotiana tabacum L.). Isopropalin (2,6-dinitro-N,N-dipropylcumidine), pebulate (S-propyl butylethylthiocarbamate), and diphenamid (N,N-dimethyl-2,2-diphenylacetamide) were applied at the recommended rates of 1.7, 4.5, and 4.5 kg/ha, respectively. Treatment of tobacco plants with isopropalin or diphenamid reduced oxidant injury for the first 2 to 4 weeks after transplanting, but not later in the season. Pebulate had no consistent affect on the sensitivity of tobacco to ozone.