Recent studies have shown an increase in fungicide resistance of important fungal pathogens in some regions.
This brings up the importance of having a good mix of fungicides, from different classes and with different modes of action. Fungicides are grouped by their modes of action, each group is given a FRAC code, a number and/or letter. Most fungicides affect a single metabolic site, single site, however some affect multiple sites, multisite.
In general, single-site fungicides are more susceptible to developing resistance than multisite fungicides, like Captan. To avoid building resistance, growers should use a combination of multi-site fungicides and single-site fungicides with different FRAC codes, avoiding applying the same FRAC more than 2 times per season. When disease pressure is high, tank-mixing multi-site and single-site fungicides can provide better control.
During drier periods, when disease infection is less favorable, growers can extend spray intervals. Maintaining good cultural control including proper row and aisle spacing to achieve adequate air circulation and light penetration will
also greatly reduce pressure.
We have had reports of growers seeing resistance with more commonly used fungicides including Elevate and Pristine. We have seen good results with Kenja but growers should speak to local extension agents for possible resistance build ups and recommendations on the best alternative for their region.