Gray Mold Control in Commercial Tomato Greenhouse Production Systems Using a Registered Biological Pesticide
1. Demonstrate efficacy of a registered biological pesticide for control of gray mold caused by Botrytis cinerea in commercial greenhouse production of tomatoes.
2. Monitor the population of dynamics of fungicide-sensitive and fungicide-resistant isolates of Botrytis cinerea prior to and after treatment with a biological pesticide in a commercial greenhouse.
3. Provide significant outreach to other greenhouse producers of tomato and ornamental crops on the economic and biological benefits associated with integrating a biological pesticide and cultural practices.
Innovative vegetable producers in the Northeast grow an increasingly diverse line of vegetables to meet consumer demands, stretch the growing season, and maximize profits. Greenhouse tomato is an attractive winter crop, but production is limited by plant diseases.
Our study focused on sustainable production of tomatoes in a commercial greenhouse using the biological control agent Mycostop (EPA Reg. #64137-2) in order to prevent stem infection by Botrytis cinerea, the causal agent of gray mold. This commercial product is a formulation of freeze-dried bacteria (Streptomyces griseoviridis) that was originally isolated from peat in Finland.
Mycostop was used in two sets of experiments – in a large commercial greenhouse and at the Experiment Station where we could inoculate with the pathogen and test cultural practices.
At the commercial greenhouse, the tomato plants (cultivar Jumbo) did not develop any signs of infection until April 12, four months after seeding. After that time, naturally infected leaves were removed weekly to prevent stem lesions, a change in cultural practices that we suggested. At the end of harvest, August 12, there were only 11 stem lesions out of 756 plants in the experiment, and none of the lesions had killed the plants. This was a dramatic improvement over the prior year, when many plants died before the tomatoes were ripe, and fruit fell to the floor because of infected, weakened fruit stems.
There was no significant difference in disease incidence or total yield due to Mycostop drenching or spraying on stems, but increased vigor and large first cluster of fruits suggested a vegetative growth enhancement effect of the biocontrol organisms. To determine whether disease was caused by fungicide-resistant strains of the pathogen, spores in the greenhouse air and from tomato leaves were cultured. The B. cinerea isolates were able to grow to some degree and sporulate on potato dextrose agar containing chloro-thalonil and dicloran at 20 ppm, the two products registered for application on greenhouse tomato in NY, but not vinclozolin, thiophanate methyl, or iprodine. A new fungal disease was found on the tomato plants at the commercial greenhouse, Cladosporium leaf spot.
Our experiments show that intervention in a commercial setting with specific data and demonstration of different cultural practices can have a significant effect on plant health; plants are more likely to die from gray mold if the leaves are not removed, and the leaves are more susceptible to gray mold than the stems.
The biocontrol agent Mycostop supplied in the irrigation dripline enhanced the vigor of tomato plants. Although tomato yield without pesticides was adequate in 1996, to keep the system sustainable over time, better management of gray mold and Cladosporium leaf spot must take place. Experimentation to compare the efficacy of many biocontrol products in the commercial setting could help to increase yields and allow growers to make a profit as they produce pesticide-free tomatoes for market.
As a result of this project, the greenhouse tomato plants surpassed the grower’s prior seasons in vigor and yield. The first clusters developed and ripened into a high May crop. Since we learned unequivocally that gray mold begins as a leaf disease and that proper deleafing can prevent stem lesions, the grower plans to permanently adopt this practice.
The pesticide-free greenhouse is a healthy environment for the tomato pickers. The tomatoes do not need washing and are sold as top quality, vine-ripened, local produce. The absence of fungicides saves the grower time and money at several steps. The microbial ecosystem was made more complex through the addition of Mycostop to the potting mix, and in addition there was no pressure to develop resistance to synthetic pesticides in Botrytis and other fungal species.
The grower was able to make a profit without the use of chemicals. In a tomato greenhouse, the only chemicals registered for use in New York are dicloran (Botran) and chlorothalonil (Exotherm, Termil). Botran causes spray injury to young leaves, and is recommended for gray mold stem lesions. Exotherm is applied as a fumigant, and works only as a protectant prior to infection. It would have to be applied weekly, and would be difficult to apply in a 10,000 square foot space. Currently, growers do not have much choice in products that are safe enough to use in a greenhouse on a food crop. Instead, they can concentrate on appropriate cultural practices such as ventilation, sanitation and deleafing, and on constant use of fertilizer enriched with calcium to enhance plant defense mechanisms.
Reported December 1996.