Figure 2: Advanced red leaf blotch symptoms. Photo credit: Alejandro Hernandez and Florent Trouillas
The good news? We have tools to fight back. Fungicides from FRAC groups 7, 11, M3, M4, and some group 3 chemistries have shown effectiveness. Consult your PCA to determine which materials best fit your orchard’s needs. Timing is just as critical as product choice. Florent Trouillas, fruit and nut crop pathology specialist with the University of California Cooperative Extension, recommends a fungicide application at petal fall, followed by additional applications at two- and five-weeks post petal fall if wet weather continues. PCAs treating the disease suggest managing it similarly to anthracnose: focus on petal fall and apply protection when rain is expected. Spraying fungicide after the symptoms appear is ineffective at controlling the disease since the infection started 35-40 days earlier. Additionally, cultural practices like removing or destroying leaf litter during dormancy can help reduce inoculum levels in the orchard.
Red leaf blotch is a serious threat to California almonds. It can have multi-year impacts on yield and tree health. But as growers, you’re adaptable. We now understand the disease’s life cycle and have effective tools to manage it. The key is action! Don’t shrug it off like I did last year. Red leaf blotch is here, and it’s here to stay.
Trent Voss, Lead Regional Manager, Blue Diamond Growers
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JULY–AUGUST 2025
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