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 (Arach is 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 dec ay 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 rain fall. No influence of temperature on decay rates could be detected. A simulation model was developed to examine the effects of new leaf emer gence on the measurement of residue dynamics. With the diluting influe nce 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 ap plications.