EFFECTS OF DINICONAZOLE ON ASPERGILLUS POPULATIONS AND AFLATOXIN FORMATION IN PEANUT UNDER IRRIGATED AND NONIRRIGATED CONDITIONS

Florunner peanuts (Arachis hypogaea) planted in irrigated and nonirrig ated plots were either not treated or sprayed four times with dinicona zole at 0.07, 0.14, and 0.28 kg/ha in 1988 and 1989. Paired plots in t he nontreated and 0.28 kg/ ha treatments were infested with a conidial suspension of Aspergillus parasiticus (a member of the Aspergillus fl avus group) or left noninfested. Populations of the A. flavus group an d the Aspergillus niger group were monitored in the soil throughout th e season as well as in the shells and seed after harvest. Treatment wi th diniconazole had no effect (P less-than-or-equal-to 0.05) on popula tions of the A. flavus group in the soil or shells, and reduced popula tions in seed only in 1989. The fungicide had no effect on soil popula tions of A. niger but reduced isolation frequencies from both shells a nd seed. Artificial infestation with A. parasiticus significantly incr eased A. flavus-group soil populations but had little effect on isolat ion frequencies from shells or seeds. Irrigation decreased isolation f requencies of both A.flavus and A. niger from shells and seed, but irr igation had no effect on soil populations of A. niger and variable eff ects on A. flavus populations. Aflatoxins were detected only in 1989. Mean concentrations were 11 and 2 ppb for the nonirrigated and irrigat ed plots, respectively. Neither fungicide treatment nor infestation wi th A. parasiticus affected aflatoxin levels. Aflatoxin concentrations were significantly correlated (P = 0.0001) with A. flavus-group popula tions in both shells and seed (r = 0.70 and 0.57, respectively).