Zoxamide

Fungicide
Zoxamide is primarily an oomycete fungicide although it has some activity against ascomycetes and basidiomycetes such as Venturia spp, Sclerotinia spp, Cercosporabeticola and Botrytis cinerea. The product has protectant and curative activity but higher application rates may be required when the product is applied curatively.

Zoxamide acts by disruption of the microtubule structure and inhibition of cell division. The mechanism for this activity is through the covalent binding of the active ingredient to β-tubulin in the cytoskeleton. There is no effect on encystment, germination or zoospore motility; however, it is proposed that zoxamide can cause a reduction in the production of viable motile zoospores. Scanning microscopy studies showed zoxamide action against blight on potato crops begins after germination, achieving inhibition of hyphal development and sporangia production. This novel mode of action makes zoxamide an important new tool in anti-resistance strategies. It is the first anti-tubulin fungicide to be used commercially against oomycetes.

Zoxamide has a strong affinity for the waxy cuticle of leaves leading to "exceptional" rainfastness. It has residual activity lasting for up to 15 days after treatment. In field trials, zoxamide controlled foliar, stem and tuber blight in potatoes. The product generally gave control equal or superior to that of established products, usually at lower application rates. A maximum of 6 applications can be made on potatoes, and 8 on grapes.

No cross resistance has been observed with other chemical types controlling Oomycete fungicides. A study of the product's effectiveness against potato blight (Phytophtora infestans) carried out on European crop isolates showed no development of resistance or decreased sensitivity to the product in crops previously exposed to zoxamide. Hence zoxamide is recommended for use in resistance and integrated crop management systems.