TEMPORAL DYNAMICS OF CHLOROTHALONIL RESIDUES ON PEANUT FOLIAGE AND THE INFLUENCE OF WEATHER FACTORS AND PLANT-GROWTH

The persistence of chlorothalonil residues on foliage of peanut (Arachis hypogaea) cultivar Florigiant was evaluated under field conditions. Chlorothalonil (Bravo 720) was applied at 1.26 kg a.i./ha with a boom sprayer. The results of seven trials over 3 yr yielded an average decay rate of -0.051 mug/cm2 per day, with values ranging from -0.093 to -0.036. This corresponds to a mean half-life of 13.6 days, with values ranging from 7 to 19 days. Decay rates increased with increasing rainfall. No influence of temperature on decay rates could be detected. A simulation model was developed to examine the effects of new leaf emergence on the measurement of residue dynamics. With the diluting influence of new leaf emergence, apparent residue half-life decreased from a true half-life of 13.6 days to 6.4 days. The model also demonstrated that because of new leaf emergence, significant amounts of unprotected foliage developed during the interval between successive fungicide applications.