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

Results and discussion

The results indicate significant effects of the biological control products on yield, disease severity, and survival of plants. The highest mean yields after 11 weeks were in the Bac-Pack and Mycostop drench treatments (Table 1). The per plant yield was significantly higher in the Mycostop drench treatment than the untreated control. Mycostop and chlorothalonil significantly reduced gray mold on leaves compared to the control. The greatest number of plants remaining at the end of the season in August was in the chlorothalonil, TopShield, and Actigard treatments.

Table 1. 1997 Disease Severity, Yield, and Survival

Treatment Disease Severity% leaf area Mean 11 week Yield (kg) Number of Plants Surviving Yield per Plant (kg)
control 4.4 b1 33.94 6.89c 4.62bc
chlorothalonil 2.4a 34.75 7.30a 4.58bc
Actigard 4.9b 31.68 7.34a 4.19c
Armicarb 12.3c 36.02 6.41d 5.29ab
Bac-Pack 4.4 b 38.89 7.18ab 5.15ab
Mycostop D 2.5a 38.44 6.59d 5.49a
Mycostop S 4.6b 37.02 6.93bc 5.00ab
Quadris 3.7ab 35.19 6.57d 5.14ab
Stylet Oil na2 33.19 7.20ab 4.57bc
TopShield 3.4 ab 35.99 7.43a 4.66bc
  LSD=1.7 ns LSD=0.28 LSD=0.77
1 Student's T test for least significant difference, alpha =0.05
2 Stylet Oil caused lesions on leaves and stems that obscured any other symptoms, so the plants in this treatment were not rated for leaf area infected with Botrytis.

The experimental products and oil could not be evaluated for powdery mildew control because the disease did not develop. Stylet Oil and Actigard increased the plant survival relative to the control, but did not increase yield. Stylet Oil was probably used at too high a rate, since damage to the plants resulted, and leaves were removed before Botrytis infections could be detected. Armacarb treated plants displayed Botrytis lesions one to two weeks before the control and disease severity was much greater, perhaps demonstrating phytotoxicity on the tomato foliage at the concentration used.

The number of plants remaining at the end of the season was used to calculate yield per plant each week. In this experiment, Mycostop increased yield by almost 2 lb (0.91 kg) per plant, which makes the product very cost-effective. The reduction in disease with a Mycostop drench was comparable to the fungicide control chlorothalonil. There is a clear advantage to the grower if fungicide use can be reduced or avoided: several practical problems are associated with pesticide application, such as awkward re-entry periods, difficulty in achieving good coverage, and compatibility with beneficial insects and pollinating bees. In addition, very few pesticides are registered for use on greenhouse tomato.

Most greenhouse tomato producers are already practicing alternative methods for disease management that reduce the need for fungicides. These strategies include the use of hot water lines running under the plants in bags of soil mix or underground (Aldrich and Bartok, 1994) so that the foliage is dried by rising warm air. They remove leaves weekly to dispose of senescing and infected leaves before fungal lesions sporulate, and have chosen greenhouse structures that allow venting of warm, moist air during cloudy and rainy weather.

All three biological control products tested in this study show promise in greenhouse tomato production. The yield and survival data support the contention that careful management in late winter and early spring when the days are short and cloudy can have an effect on the entire season. Consistent deleafing prior to sporulation and application of biological control products before fruit set can significantly increase survival and per plant yield. The next step in this project is to try combinations of these sprays and drenches to reduce disease, increase the number of plants remaining at the end of the season, and also increase per plant yield.