Evaluation of Fungicides and Bactericides for Control of Late Blight and Bacterial Spot in Tomatoes, 2000

P.D. Roberts
Plant Pathology Department
University of Florida
SWFREC
Immokalee, FL 34142

TOMATO (Lycopersicon esculentum 'Sunnyland 814)
Early blight (Alternaria solani)
Late blight (Phytophthora infestans)
Bacterial spot (Xanthomonas campestris pv. vesicatoria)

The experiment was located at the Southwest Florida Research and Education Center in Immokalee, FL. The soil was Immokalee fine sand (97:2.5:0.3% sand-silt-clay, pH 4.2, O.M. 1.96%) Raised plastic beds were prepared on 11 Feb by fumigation with 300lbs/A 67/33 methyl bromide/chloropicrin and fertilized with a bottom mix of 800 lb of 5-16-8 fertilizer/A. The top mix of 800 lb of 19-0-19 fertilizer/A was applied in two bands on the bed top. Beds were on 32" centers and spaced 6 ft between beds. Six-week-old seedlings of tomato cultivar 'Sunnyland 814' obtained from Johnson Transplants, Immokalee, FL, were transplanted to the field on 28 Feb. Treatments were arranged in a randomized complete block with 4 replications. Plots were 30 ft long with 18" plant spacing and 5 ft buffer between plots within the row. Fields were watered by seep irrigation. Pesticides for arthropod insects (Ambush 6 oz/A) and whitefly (Admire 16 oz/A) were applied according to label. The fungicide and bactericide formulations, rates, and application intervals are presented in the table. All compounds were applied with a backpack CO2 sprayer at 40 psi with a flat spray tip nozzle at 23.6 gal/A. The center plant in each plot was inoculated with a suspension of zoospores (approximately 106 spores/ml) of Phytophthora infestans on 14 Apr. Two cultures of Xanthomonas campestris pv. vesicatoria representing tomato race 1 and 3 were grown overnight in nutrient broth and adjusted to approximately 10 8 cfu/ml and applied to all plants by a hand pump sprayer on 14 Apr. Disease readings were taken at 2-week intervals throughout the season by an estimate of disease severity (DS) as percentage of foliage exhibiting symptoms. Disease symptoms were partitioned into late blight and bacterial spot. Fruits were harvested on 18 May. Yields were normalized for plots containing missing plants.

Symptoms of early blight, late blight and bacterial spot were observed throughout the season. Severity of bacterial spot remained low despite application of inoculum and significant differences were not detected. Disease severity of early blight and late blight were also generally low although a significant difference in reduced disease severity was observed between the control and 75% (15 out of 20) of treatments. Environmental conditions were not conducive to disease development and sufficient irrigation was difficult to maintain due to low rainfall and days with high temperatures. Overall these conditions compromised plant heath and yield and fruit quality were reduced. No significance differences were observed between the number of fruit harvested nor weight of fruit.

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