MANAGEMENT OF DISEASES IN VEGETABLE AND SPECIALTY CROPS

Florida ranked first in the U.S. in acreage for the production of fresh market tomatoes, squash, and watermelon in 2015 and second in bell peppers and cucumbers (USDA Vegetables Summary, 2016). Florida growers receive more than USD $450 million in sales of tomato, $220 million in bell pepper, and $163 million in cucurbits (watermelon, cucumber, and squash). Southwest Florida is a leading producer of vegetables including pepper, watermelon, cantaloupe, squash, corn, cucumber, potato, tomato, and snap bean during the winter months in the USA. A large transplant industry for vegetables is located in the region. Additionally, there are ornamental and palm nurseries, herb producers, organic growers, and various specialty crops. This wide diversity of crop species can be subjected to a number of limiting plant diseases, most of which are favored by Florida's subtropical climate of warm and wet environmental conditions favored for rapid disease development.Losses incurred by diseases can impact productivity by 10-50% in any given year.Knowledge of the pathogen, the disease cycle, and the environmental conditions that favor disease outbreaks is essential to formulating effective control tactics.The goals of this part of my research program are to develop environmentally compatible disease management tactics by investigating novel approaches and evaluating management programs. This research investigates the use of novel compounds, systemic acquired resistance (SAR) inducers, new chemistries, soil treatments, biological control, cultural control methods, host resistance, and reduced-rates of pesticides combined.

In vitro, In vivo, and field testing to evaluate efficacy for novel or other compounds for suppression of plant disease. In order to prepare bacteria for testing, bacterial suspensions will be prepared by suspending 24-h cultures in a sterile phosphate-buffered salin. For in vitro assays, the suspensions will be adjusted to an absorbance of 0.3 at 600 nm (5x108 CFU/ml). Bacterial suspensions will be combined with the chemical suspensions in test tubes at a ratio of 1:1 (vol:vol). Test tubes will be placed on a shaker platform. Following shaking, suspensions will be filtered with a sterile Whatman no. 1 filter paper. The filtrate will serially be diluted and a 20-µl aliquot of appropriate dilutions will be plated on media in petri plates. There will be three plates per dilution series. Plates will be incubated at 28°C for 3 days. Colonies will be counted and differences among treatments assessed using SAS. Fungal cultures will be maintained on potato dextrose agar and transferred one week prior to use to new plants. Cultures will be microscopically examined for conidia or other spores and enumerated if needed prior to inoculation from suspension. Seedlings of the host will be transplanted in the greenhouse to pots containing a commercial soil mix Fafard no. 2 (Conrad Fafard, Inc., Agawan, MA.). Each pot will receive 5 to 10 g of a slow-release fertilizer (Osmocote, 15-9-12; Sierra Chemical Co., Milpitas, CA). Plants at 3-4 weeks of age will be sprayed with the test suspensions using a hand-held pump sprayer. Controls will be untreated. Leaves will be challenged with the bacterial suspension. All plants will be immediately enclosed in transparent, polyethylene, plastic bags for a 48-h period. The bags will be then removed and plants will be returned to the greenhouse in a randomized complete block design. The plants are rated after 14 days for either disease incidence or disease severity. The experiment will be repeated twice. Plants (tomato, pepper, watermelon, and/or squash) will be transplanted into fields at the SWFREC, Immokalee, FL. Treatments are arranged in a randomized block design with four replications. Each plot consists of 15-20 plants. Guidelines established by the University of Florida/IFAS will be followed for land preparation, fertility, irrigation, weed management and insect control. Sprays will be applied with a high clearance sprayer designed specifically for applications in staked tomato plots at 2 mph and at 200 psi. A double drop boom equipped with 6 nozzles delivers a spray volume of 66 gal/A or with a backpack sprayer and hand nozzle. Disease ratings as disease severity (percentage symptomatic tissue) or disease incidence will be assessed through the season at 7- to 14- day inverals. The differences will be examined between means by Least Significant Difference (LSD) using SAS.