Evaluation of fungicides and bactericides for control of Phytophthora blight and bacterial spot pepper, 1999

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

Pepper (Capsicuum annuum var annuum)
Bacterial spot (Xanthomonas campestris pv. vesicatoria)
Phytophthora blight (Phytophthora capsici)

Evaluation of fungicides and bactericides for control of Phytophthora blight and bacterial spot pepper, 1999. The trial 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 20 Sept 99 after fumigation with 67/33 methyl bromide/chloropicrin at 300 lbs/A. Plots were fertilized with a bottom mix of 800 lbs/A of 5-16-8 and a top mix applied in a double band on the bed top of 800 lbs/A of 19-0-19. Beds were 32" centers and 6 ft between beds. Plant spacing was 18" between plants with two rows per bed width. Plots consisted of 20 plants each and spaced 20 ft apart. Experimental design was a complete randomized block treatment design. Six-week-old seedlings of pepper cultivar 'Enterprise' were transplanted to the field on 4 October 99. Fields were watered by seep irrigation. Pesticides for insects (Vydate) and weed control (Paraquat) were applied as needed at labeled rates. Compounds that were drip applied were injected through standard drip tape located down the center of the row of each plot. Chemicals were injected using a CO2 cartridge and nozzle connected to the end of the drip at 500 psi until soil was thoroughly drenched. Compounds that were applied to the foliage was with a backpack CO2 sprayer at 40 psi with a single hollow cone nozzle at 23.6 gal/A. Four plants at each end of the plot were inoculated with zoospore suspensions of Phytophthora capsici at 6 weeks after transplanting. All the plants in the plot were inoculated with a suspension of Xanthomonas campestris pv. vesicatoria at a concentration of 108 cfu/ml. Disease readings were taken at two-week intervals using a modified Horsfall-Barrett scale estimating the disease severity (DS) as percentage of foliage exhibiting symptoms. Plants wilted or dead were recorded at two-week intervals. Fruits were harvested three times. Yields and disease severity ratings were subject to ANOVA and the means tested for significance using Duncan's Multiple Range Test.

The results are presented in the table. The treatments containing Champ and Kocide formulations were applied to the foliage. Ultra Flourish was applied to the soil for control of Phytophthora blight. However, disease readings for both diseases were made for all treatments. The pepper plants had very little to no bacterial spot at the end of the season. Disease readings at 62 days after transplanting were very low (1-2% disease severity) and there were not significant differences between treatments. Plant inoculated with P. capsici usually exhibited wilting and death within 14 days, however, intraplot spread was minimal. Phytotoxicity as chlorosis and stunting was observed on plants treated with Ultraflourish. In previous trials, plants treated with Ridomil Gold-type compounds also turned yellow and were stunted until 4 weeks after transplanting. The method of application in the small trial plots appears to be too efficient for rates recommended to commercial operations. The plants treated with Ultra Flourish had slightly less plant mortality compared to the control but was not clearly separated statistically. Both the number and weight of the fruit were reduced for the Ultra Flourish treatment however yields overall were not significantly different.

Back