Metalaxyl is a systemic fungicide used to control plant diseases caused by Oomycete fungi. Metalaxyl is a racemic mixture of two isomers, one of which, the R-enantiomer, is the active form. This enantiomer is the basis of the fungicide, metalaxyl-M (mefenoxam), which is effective at half the application rate of metalaxyl. This was developed by Syngenta as a replacement for metalaxyl, and was part of a strategy to stifle generic competition. Metalaxyl`s formulations include granules, wettable powders, dusts, and emulsifiable concentrates. Application may be by foliar or soil incorporation, surface spraying (broadcast or band), drenching, and seed treatment. Metalaxyl registered products either contain metalaxyl as the sole active ingredient or are combined with other active ingredients (e.g., captan, mancozeb, copper compounds, carboxin). Due to its broad-spectrum activity, metalaxyl is used world-wide on a variety of fruit and vegetable crops. Its effectiveness results from inhibition of uridine incorporation into RNA and specific inhibition of RNA polymerase-1. Metalaxyl has both curative and systemic properties. Its mammalian toxicity is classified as EPA toxicity class III and it is also relatively non-toxic to most nontarget arthropod and vertebrate species.