EVALUATION OF FUNGICIDES AND PROPHYLACTIC TREAMENTS FOR CONTROL OF POWDERY MILDEW ON BEIT ALPHA CUCUMBER, 2004:

A trial was conducted in a plastic-covered, screened, high-roofed, passively-ventilated 1-acre greenhouse at the Protected Agriculture Project, Plant Science Research and Education Center, Citra, Florida.  Seed was planted on May 7, 2004  in a Conviron and transplanted on May 28, 2004, when the Beit Alpha cucumbers were at the three-leaf stage. Transplants were set into pine bark media in 11.4 L black polyethylene nursery pots drained through 4 1.5-cm-diameter drainage holes,  two inches above the base. The pots were placed with rows at 1.2 m and 40 cm from center to center of each pot. Plants were irrigated using a complete nutrient solution based on the University of Florida’s recommendations for greenhouse cucumber. The irrigation schedule was determined upon collection of 10 to 20% leachate from the plants over a 24 hour period.  Insect pests, two-spotted spider mite (Tetranychus urticae Koch), whiteflies, Bemisia tabaci and cotton aphids, Aphis gossypii were controlled by releases of Neoseiulus californicus, Encarsia spp. and Eretmocerus mundus,  and Aphidius colemani respectively. The experiment occupied one bay of the greenhouse with five rows. The two border rows were planted with cultivar “Meitav”. Experimental units were 3 plants (cv “Sarig”) separated by three unsprayed plants (cv “Meitav”) to ensure amplification of inoculum and to promote good conditions for disease. The experiment was conducted as a randomized complete block design with three replications. Treatments were applied using an air-assist sprayer applied to run off. Treatments were applied every 7 days starting on June 9 and ending on July 7.  Plots were rated once each week for five weeks.  Disease ratings were recorded as percent area of leaves with powdery mildew disease symptoms.  Final area under the disease progress curves (AUDPC) were generated from these data and means separated using Fisher’s protected least significance difference (LSD) test. Fruit was harvested every other day starting on June 15 and ending on July 15.

Environmental conditions were conducive to promote powdery mildew development and inoculum levels were high due to powdery mildew infection on border plants.  Initial disease ratings of were zero but increased over the course of the experiment. Potassium bicarbonate (Milstop), Seaweed extract (Sea Crop 16 - NAK), and Sulfur (Microthiol Disperss) along with the fungicide - Quadris or Nova (+ control), significantly reduced the final AUDPC as compared to the untreated check. Marketable yield was significantly higher with Seaweed extract (Sea Crop 16 - NAK), and Sulfur (Microthiol Disperss) compared to the untreated control. No phytotoxicity was observed apart from an initial treatment with sodium bicarbonate.

¹Values are mean of three replicates. Means followed by the same letter are not significantly different according to Fisher’s Protected LSD (P=0.05)