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Microbial and Synthetic Products for Management of Botrytis Grey Mold in Tomato

Materials and methods

Tomato plants (cv. Jumbo) were grown in Metro Mix 250 (Grace Horticultural Products, Cambridge, MA), and watered with a constant feed solution of Peter's Hydrosol (5-11-26, 13.0 oz/100 gal, Scotts Co., Marysville, Ohio), and calcium nitrate (5.3 oz/100 gal). Increasing amounts of fertilizer were added during the season, including magnesium nitrate and soluble iron as indicated by foliar nutrient analysis. The seedlings were transplanted into 4 inch pots, and then into upright bags with drainage holes containing 4 gal potting mix. The constant feed irrigation was delivered through drip lines with one emitter per bag. The plants were arranged in double staggered rows, resulting in about 4.0 sq ft per plant.

The project utilized one 28 x 96 ft section of a four-bay gutter-connected greenhouse. The thermostat of the heating system was set to maintain an air temperature greater than 65° F, with natural gas heaters mounted about 3 ft above the floor. The roof of the greenhouse was raised on sunny, hot days to provide cooling and ventilation. In addition, fans were installed to provide horizontal air movement. The indeterminate plants were each supported with a 14 ft string coiled on spool hooks on wires at 7 ft (2.3 m) above the floor. The plants were lowered incrementally whenever they reached the wire. Routine maintenance included twisting the support string around each plant, fastening the stem to the string with plastic clips after each flower cluster, and removing axial shoots. Deleafing took place weekly when lower leaves began to senesce, at about the time that green fruits reached full size. Flowers were pollinated by imported bumblebees. Tomatoes were picked red ripe; each treatment and replication was weighed separately.

The experiment was a randomized complete block design consisting of 4 blocks and 10 treatments. Each cell of the design contained 8 plants. The treatment arrangement was randomized to counteract the location effects observed the year before. Three microbial products, Mycostop, TopShield, and Bac-Pack, were compared to the new products Actigard, Armacarb, and Quadris, to Stylet Oil, to an untreated control, and to the fungicide control, chlorothalonil (Bravo was used for local application instead of Exotherm Termil canisters) to determine if they had an effect on disease incidence or severity and on yield. Mycostop was applied separately as two treatments, a spray and a drench. Each treatment was applied twice before fruit set, on March 19 and April 8 (crop was seeded Jan. 2). The fruit from plants treated with materials under an experimental use permit were removed from the premises for crop destruct.

The biological control products were prepared as recommended by their manufacturers. Mycostop was rehydrated, suspended, and strained before application (1 g/2 L water, 50 mL per plant). TopShield was applied at the rate of 40 g/2 L water (including the surfactant supplied by BioWorks). Bac-Pack was applied as a drench, at 2.35 ml/2 L. Actigard (CGA 245704, Novartis Crop Protection Inc., Greensboro, NC,) was applied at the rate of 50 mg/2 L. Armacarb 100, a potassium bicarbonate product (formula 2346-102 Church and Dwight Co, Inc., Princeton, NJ) was used at 6.5 g/2 L. Quadris (Zeneca, Ag Products, Wilmington, DE) was applied as the flowable product, 0.35 mL/2 L. The horticultural oil, JMS Stylet Oil (JMS Flower Farms, Inc., Vero Beach, FL) was applied at 1.5%, 30 mL/2 L water. The fungicide chlorothalonil was applied to the foliage as a Bravo Weather Stik spray treatment (1.4 mL / 2 L).

Natural inoculum was available in the commercial greenhouse; plants were not artificially inoculated. The presence of B. cinerea spores was verified by placing open Petri plates of potato dextrose agar on the floor of the greenhouse for 2 h, then returning the plates to lab for incubation at room temperature for 10 days.

Disease severity on the leaves was assessed each week for five weeks beginning April 7. Very few infected leaves were observed until the third rating, April 22. After this time, the oldest leaves were removed, the number of infected leaves was counted, and the percent leaf area infected was estimated. A very cool, cloudy spring delayed the ripening of tomato fruit until May 21; thereafter, tomatoes were harvested three times a week for 11 weeks. Statistical analysis of the yield data and disease assessment was carried out by analysis of variance.