Bunch rot

The third group of new fungicides to be tested on grapes in the US is the dicarboximide group. Vinclozolin (Ronilan) and iprodione (Rov-ral) are the members of this group that have been extensively tested for control of Botrytis bunch rot. 

Pearson, R. C., and D. G. Riegel. 1983. Control of Botrytis bunch rot of ripening grapes Timing applications of the dicar-boxlmide fungicides. Am. J. Enol. Vitic. 34 167-172. 

Various grape-picking strategies and techniques are applied in botrytized wine making. Regardless, a prolonged or late harvest is necessary a factor which implies risk of losing the crop to bunch rot, other infections or frost under adverse weather conditions. 

Fruit clusters enveloped with a fluffy, gray-brown coating. Cause Botrytis bunch rot. This fungal disease appears in tight fruit clusters and in vines with poor air circulation. For prevention, thin berries within clusters and remove some leaves around fruit. Clean up prunings, cluster stems, and mummified fruit by early spring. Plant resistant cultivars, including Baco No.r, Cascade , Catawba , Concord ,... 

Where conditions within and surrounding the cluster remain wet and the relative humidity high (>90%), berry dehydration does not occur. Thus, the concentration of grape sugars either remains the same or decreases. In this scenario, growth of Botrytis and secondary molds, native yeast, and bacteria rapidly ensues, resulting in sour bunch rot. 

Aspergillus begins as a white mycelium similar to Penicillium, but as conidia mature, the colony develops a black coloration. Microscopically, conidiospores are borne in chains at the apex of flask to knob-shaped vessicles called sterigmata. A. niger plays an important role in rot, particularly in warm climates. This feature has led to its description as the hot weather mold. Aspergillus, Rhizopus, and Acetobacter represent the important members the summer bunch rot complex. 

Variable proportions of bunch rot can coexist with noble rot. The involvement of acetic acid bacteria results in the production of volatile acidity. Gray rot can also form odors and tastes resembling mushrooms, mold, iodine and phenol. In addition, considerable amounts of carbonyl-based compounds may be produced, which bind sulfur dioxide and make these wines difficult to stabilize. 

S.V. 23-512. Most of the commercial success with this selection is in Ontario, where it has been used for blending into inexpensive white wines. Vines are vigorous, productive and resistant to disease. Clusters are large and relatively tight, with large oval berries, ft is normally resistant to bunch rots. Wines are typically neutral. 

Osceola Muscat helps fill the need for a cold hardy white Muscat cultivar but has issues in some years with poor set, splitting, and bunch rot. 

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