Fruit Crops

Fungus Applications Control Botrytis Bunch Rot of Grape

The fungus Botrytis cinerea, that causes the diseases called bunch rot of grape and gray mold on other crops, normally must be controlled with fungicide sprays. Several strains of the beneficial fungus Trichoderma harzianum were evaluated in upstate New York and Chile in the early 1990's for their ability to control bunch rot on grape.

As with previous field trials, Trichoderma gave significant disease control, but wasn't always as effective as sprays of the commonly-used fungicide iprodione. All the different strains of the fungus tested gave control, but one strain was less consistent than two others. The quality and composition of the spore preparations used in the sprays makes a big difference; efforts are underway to produce suitable and effective formulations for spray applications. The role of nutritive stickers needs more investigation, but Pelgel (a mixture of carboxymethyl cellulose and gum arabic made by Liphatech, Milwaukee, WI) applied with the biocontrol fungi tended to improve results.

As few as two late applications of the biocontrol fungi were nearly as effective as up to five applications throughout bloom and fruit development. Many strains of Trichoderma are compatible with the iprodione, so this biological control agent could be used in tank mixes or alternating sprays to reduce chemical inputs when Trichoderma alone is inadequate. In one year's tests, applications of Trichoderma at bloom and early fruit development followed by half rates of iprodione gave extremely effective control of bunch rot, while in another year this was not as effective. The combination of three applications of the biocontrol agents followed by a tank mix of Trichoderma and the chemical gave control at low total pesticide rates.

Source: Harman, G. E., B. Latorre, E. Agosin, R. San Martin, D. G. Riegel, P.A. Nielsen, A. Tronsmo and R. C. Pearson. 1996. Biological and Integrated Control of Botrytis Bunch Rot of Grape Using Trichoderma spp. Biological Control 7(3): 259-266.

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