2019 ASHS Annual Conference

Hydroponically-grown leafy green production is a fast-growing area in the greenhouse industry that allows year-round access to fresh, local produce. Powdery mildew is a fungal disease, which harms a wide variety of plants including hydroponic crops. The disease is prevalent in environments with dense foliage, restricted airflow, high humidity, and moderate temperatures which are common conditions in greenhouse crops including lettuce. Growers currently experience significant crop loss and yield reductions in hydroponic lettuce due to powdery mildew. Application of calcium chloride (CaCl₂) has been reported to control other fungal diseases like grey mold. We investigated the efficacy of calcium chloride in controlling powdery mildew disease on hydroponically grown lettuce cultivar (Lactuca sativa ‘Salanova® Green Butter’) known to be susceptible to powdery mildew. The first experiment was conducted in a high humidity growth chamber with plants treated with either 0 or 800 mg∙L^-1 CaCl₂ twice a week. The average number of infected leaves per plant was seven in the 800 mg∙L^-1 treatment as compared to 23 in the control. The second experiment was conducted in the greenhouse and the plants were treated with either 0 mg∙L^-1 or 800 mg∙L^-1_, either lab-grade or commercial-grade. The average number of infected leaves per plant was eight and six following application of lab grade and commercial grade CaCl₂ as compared to control with twenty leaves. A 60 g reduction in yield was noted following application of lab grade CaCl₂. Foliar sprays of CaCl₂ reduced powdery mildew disease severity in hydroponically grown lettuce ‘Green Butter’. Calcium chloride is readily available to growers and will provide a viable alternative to fungicides for the control of powdery mildew on hydroponic lettuce.