Effect of temperature and humidity on the formation of dibutylurea in benlate fungicide

Benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate] is the active ingredient in DuPont Benlate fungicides. The formation of N,N'-dibutylurea (DBU), a phytotoxic degradation product of benomyl, in Benlate formulations was evaluated by analyzing Benlate samples maintained under simulated stor age conditions and assessing the effects of temperature and humidity on sam ple moisture content, benomyl degradation, and the rate of DBU formation. B enomyl degraded during storage by the elimination of n-butylisocyanate (BIC ) to form methyl 2-benzimidazoIe carbamate (MBC; carbendazim). Liberated BI C could then proceed to react with water to form DBU (first-order rate cons tant of 8.4 x 10(-4) s(-1)). The degradation of benomyl and subsequent form ation of DBU were dependent on the temperature and highly dependent on the humidity of the storage environment. At the lower humidity storage conditio ns the rates of DBU formation were significantly higher in the dry flowable (DF) formulation than in the wettable powder (WP) formulation. The initial moisture content of Benlate DF samples was higher than those of Benlate WP samples, although the Benlate WP samples absorbed more moisture upon incub ation. These results may yield insight on the appearance of high levels of DBU found in some boxes and bags of Benlate DF and Benlate WP formulations.