Evaluation of biocontrol agents and potassium silicate for the management of powdery mildew of zucchini

• Biocontrol agents and silicon reduced the severity and AUDPC of powdery mildew.
• Temperature, RH and disease pressure affected efficacy of BCAs and Si.
• Clonostachy rosea and Trichothecium roseum performed well under extreme conditions.
• Application of K2SiO2 increased accumulation of Si in zucchini leaves.

Investigations were conducted under greenhouse and field conditions to evaluate the effects of potential biocontrol agents (BCAs) and soluble silicon (Si) on powdery mildew of zucchini caused by Podosphaera xanthii. Five BCAs were applied as foliar sprays to zucchini leaves and Si was drenched weekly into the rhizosphere of these plants.In the greenhouse, all BCAs provided significant control of powdery mildew with fungal isolates, reducing disease levels by up to 90%. Si alone reduced powdery mildew by as much as 35% and improved the efficacy of most of the biocontrol agents. Higher disease pressure reduced the efficacy of Si on powdery mildew but did not affect the performance of the BCAs. In the field, a disease reduction of 10–70% was achieved by BCAs and Si. Lower temperatures and high humidity ranges were suitable for optimal performances. The efficacy of the bacterial BCA, Serratia marcescens – B15 and silicon diminished at temperatures above 25 °C. The fungal BCAs (Clonostachys rosea – EH and Trichothecium roseum – H20) were better suited to higher temperatures (25–30 °C) and were tolerant of low RH values. Application of K2SiO2 to zucchini roots increased the level of Si in the leaves, which was responsible for suppression of the disease.

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