Top greenhouse powdery mildew control strategies

Understanding the preferred environmental conditions for the pathogen is the first step to control. Moderate temperatures and high humidity environments promote powdery mildew outbreaks. Unfortunately, beneficial environments for this pathogen overlap quite a bit with typical growth conditions for many crops. Spores germinate under high humidity conditions with dry leaf surfaces, while low humidity conditions promote the dispersal of spores.

Managing humidity levels provides a critical control strategy to growers. Maintaining constant humidity levels between 55% to 60%, or 65% to 75% when using beneficial insects, slows powdery mildew germination and dispersal. Proper use of horizontal airflow fans promotes effective mixing of air, helping to eliminate pockets of high or low humidity within the canopy.

Maintaining proper fertility is a second foundational step to help crops resist initial infection. Excessive nitrogen can lead to production of soft growth that is more prone to disease infection. Beyond basic management of primary nutrients, certain supplementary nutrients can improve disease and pest resistance. There is some anecdotal evidence that calcium foliar sprays provide some suppression of powdery mildew but would not be a curative choice. Silica supplements have been shown to strengthen cell walls, improve stress tolerance, and improve resistance to foliar disease in silica-sensitive plants. Some silica products are EPA-labeled insecticides and miticides and include a number of food crops on the label.

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Source: Greenhouse grower