Plots treated with BAS-500, BAS-510, and with Dithane alternated with Quadris had significantly lower disease ratings for Early and Late Blight and the highest marketable yield than the other treatments. Plots treated with Seranade (biological fungicide) had disease ratings not significantly different than the untreated check plots.

Early Blight has continued to be an annual problem in tomato production in Tennessee. Tomatoes are widely grown in Tennessee and blight, which thrives under the extremely humid weather conditions of this state, present a major concern for growers. Therefore, thirteen fungicide treatments were evaluated for control of Early and Late Blight at the University of Tennessee Plateau Experiment Station in Crossville in 2001. Tests have been conducted for several years to evaluate different disease management strategies which include; rate adjustments, chemical combinations and alternate use of certain chemicals. The major commercial control strategies for both Early and Late Blight control have been a preventative spray program with fungicide applications made on a seven day schedule depending on weather conditions. Late Blight development is dependent upon a very strict set of weather conditions. Cool, wet, cloudy conditions favor Late Blight development. Therefore, frequent fungicide applications, usually on a seven day schedule, are imperative for acceptable disease control and successful crop production. However, a new strain of Late Blight has emerged which has proven difficult to control. This new strain, resistant to several fungicides, has been identified as the A2 strain.

Materials and Methods

Thirteen foliar fungicides were evaluated for control of Early and Late Blight in tomatoes at The University of Tennessee Plateau Experiment Station, Crossville. Fertilization consisted of 600 lb/A 15-15-15 applied broadcast and disc incorporated on 14 May. ‘Mountain Fresh’ plants were transplanted on 17 May. Standard weed and insect control practices were implemented during the growing season. Plots consisted of single rows 10ft wide and 15ft long with10 plants/row. Treatments were replicated 4 times in a randomized complete block design. Fungicides were applied on a weekly schedule starting on 25 Jun and ending on 15 Aug. Applications were made using a 2.5 gal CO₂ backpack sprayer calibrated to deliver 60 gal/A at 60psi early season and 120 gal/A at 100psi late season. Weekly disease ratings ranged from 0 (no disease incidence) to 10 (100% leaf defoliation). Yield data were compiled from multiple harvest dates. All data were subjected to ANOVA.

Plots treated with BAS-500(0.15 lb ai/A), BAS-510, BAS-500 alternated with BAS-510, and BAS-500 alternated with Bravo Ultrex had significantly lower disease ratings for Early Blight than any other treatment (Table 2 ). Plots treated with BAS-500 alternated with BAS-510 had significantly lower Late Blight disease ratings than the other treated plots (Table 3 ). All plots treated with fungicides except plots treated with the biological fungicide Serenade had significantly lower disease ratings for Early and Late Blight, and higher marketable yield than the untreated check plots. After the last fungicide application, plots treated with Dithane, Dithane alternated with Quadris, and Bravo Ultrex tank mixed with Dithane had significantly lower early blight disease ratings than any other fungicide treatment. All plots treated with a fungicide had significantly lower disease ratings than the untreated check plots. Late blight symptoms were apparent late in the growing season and all plots treated with a fungicide had lower disease ratings than the untreated check plots. Plots treated with both rates of BAS-500, BAS-510 , BAS-500 alternated with BAS-510, BAS-500 alternated with Bravo Ultrex, and Dithane alternated with Quadris produced more Marketable Tomatoes (# 1 + # 2) than any other treatment. Plots treated with Dithane, Flint alternated with Bravo Ultrex, Bravo Ultrex tank mixed with Dithane, and Bravo Ultrex alone produced significantly more # 1 tomatoes than the untreated check plots (Table 4 ).

Table 1. Spray schedule for tomato fungicide efficacy trial .

Table 2. Early Blight Rating (0 - 10) of ‘Mt Fresh’ Tomatoes Receiving Various Fungicides at The University of Tennessee Plateau Experiment Station, Crossville, 2001.