ABSTRACT
This chapter summarizes what is known of the variable environmental factors and how they impinge upon the activity of the imidazolinone herbicides. Several studies indicate that temperature plays an important role in the activity of the imidazolinone herbicides. Differences in crop tolerance and weed control have been observed with imazamethabenz-methyl, imazaquin, imazethapyr, and imazapyr. Imazethapyr was tested under various temperatures to determine the effect of temperature on phytotoxicity in soybeans and alfalfa. After soil application, rainfall is required for good activity of most herbicides, including the imidazolinones. It has been widely observed with the imidazolinones that poor activity may result if inadequate rainfall is received after preemergence and, sometimes, preplant-incorporated applications. Soil moisture is an important factor. Increased uptake of imazaquin by corn and imazamethabenz-methyl by wheat has been demonstrated with increased soil moisture, particularly under conditions of excess soil moisture.
