Alternaria Leaf Spot Control Strategies

Warmer than average temperatures have accelerated almond crop development and triggered early bloom in many areas.

Jeff Pacheco, a DuPont Crop Protection technical sales agronomist, offers recommendations to help navigate another year of unpredictable growing conditions.

“Almonds are bringing such premiums that growers will want to minimize risk and be proactive with disease-control programs.”

Alternaria Leaf Spot

Alternaria leaf spot pressure can be a very serious disease in some areas and more severe in some years than others, affecting almonds in the southern San Joaquin Valley and northern Sacramento Valley. “Alternaria is better understood than it was several years ago,” says Pacheco. “We know development is heavily influenced by weather events and orchard microclimate.” Prolonged leaf wetness makes almond trees (especially Carmel, Sonora, Monterey, Winters and Butte varieties) more susceptible to Alternaria infection.

Early summer infections typically appear as large leaf lesions (brown spots) and premature defoliation can result, limiting the following year’s crop. Extreme heat, rain, dew, high ambient humidity below the canopy, dense plantings and frequent irrigation create the perfect environment for Alternaria.

Disease Control Post Petal Fall

Scab, rust and powdery mildew join Alternaria as summer diseases that demand attention once petal fall is complete. No fungicide is effective on all diseases, so growers need to implement a rotation plan or use prescriptive fungicide tank mixtures to manage diseases and minimize resistance.

“Your PCA and DuPont representative can help you set a disease-control plan for the entire season so you’re ready for whatever Mother Nature throws at you,” says Pacheco. “Preparing for the worst allows you to get the most from your crop.”

Single Mode of Action

An excellent option for Alternaria control, DuPont™ Fontelis® fungicide provides broad-spectrum control of many damaging blossom-to-late-season diseases, including brown rot blossom blight, anthracnose, botrytis rots (jacket rot/green fruit rot) and shot-hole. Formulated with a single active ingredient for flexibility, Fontelis® penetrates plant tissue quickly and delivers lasting protection with pre- and post-infection activity.

“Many PCAs recommend that Fontelis® be the first fungicide applied five weeks post petal fall because it’s easy to build a rotation program around,” notes Pacheco. “And Fontelis® is compatible with most commonly used fungicides, insecticides, liquid fertilizers and biological control products, so it can also be used in a tank mix.”

DuPont™ Fontelis® is not registered in all states. Contact your DuPont representative for details and availability in your state.


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