Nursery treatments with non-conventional products against crown and root rot, caused by Phytophthora capsici, on zucchini

Phytophthora capsici, a pathogen causing crown and root rot of zucchini in southern Italy since the 1980s, has recently been observed in open field in northern Italy, causing severe losses. Since chemical control on zucchini is complicated by a limited availability of registered chemicals, as well as by the scalar harvest, a number of resistance inducers, organic amendments, biocontrol agents and fungicides were tested against P. capsici, under greenhouse conditions. Experiments were carried out at the nursery level, with different timing and number of applications. In the presence of a very high disease pressure, the best disease control was provided by mefenoxam, followed by the phosphite-based products, which acted as resistance inducers and also provided a positive effect on plant biomass. Acibenzolar-S-methyl, although effective, was sometimes phytotoxic. The biocontrol agents tested as well as the patented formulation of Brassica carinata defatted seed meals were not effective, providing results statistically similar to the untreated control. The efficacy of resistance inducers is interesting in view of their possible use in alternation with chemicals, or as stand-alone treatments in cultivation systems which do not adopt chemical control.