EFFECTS OF SOIL-INCORPORATED INSECTICIDES AND FOLIAR-APPLIED CHEMICALS ON CORN GAS-EXCHANGE PARAMETERS

A 2-year field study was conducted to examine the effects of pesticide applications on key field corn (Zea mays L.) plant physiological parameters. The influence of five soil insecticides, applied at planting time, and ten foliar-applied chemicals (eight insecticides, one acaricide, and one plant growth regulator) on corn photosynthetic rate and stomatal conductance was evaluated. Of the soil insecticides. trimethacarb had the greatest effect on photosynthetic rate (reduction by as much as 18.9%). This reduction persisted for 54 days after application in 1988. Effects of the other soil insecticides on photosynthesis were transient, i.e. stimulant on photosynthesis at some sample dates and inhibitory at other sample dates. Carbaryl (flowable formulation) and methidathion had the most serious effects of the foliar pesticides on plant physiology, although all the toxicants significantly reduced the corn photosynthetic rate during at least one sampling period. Stomatal conductance was affected in a manner similar to that of photosynthetic rate by the pesticides, but to a lesser degree. The interaction of chemical treatments with environmental conditions, especially soil moisture, was apparently an important factor in the plant responses.