New information about Botrytis bunch rot, a key cause of crop loss to producers of wine and table grapes, has resolved conflicting models of its development and improved programs designed to control the disease.
Botrytis bunch rot (BBR) is a serious disease of wine and table grapes that leads to direct losses in the field, storage rot, and poor wine quality. U.S. producers spend over $10 million, and apply nearly 200,000 pounds of fungicide, to control BBR every year.
BBR is among the least understood fungal diseases of grapes. In New York, fungicidal control recommendations traditionally emphasized the period from veraison, or the start of ripening, through harvest; however, in many other wine-producing regions of the world, fungicide is applied preferentially during the bloom period. This disparity reflects two fundamentally conflicting models of disease development. One model claims that most infections occur during bloom but remain latent until preharvest, when they become active and rot the grapes. This has been shown for Botrytis disease of strawberries. According to the other model, however, most infections occur during the preharvest period.
In addition to fungicide applications, disease control is typically supplemented by cultural practices. According to variety and region, these practices may include altering the microclimate around clusters, loosening cluster compactness, regulating vine nutrition, and regulating the water available to vines. However, many of these practices have been employed on an empirical basis, and the biological bases for their success, or lack thereof, are generally unknown.
The purpose of this project was to elucidate several biological bases of BBR development in order to improve both chemical and non-chemical control methods.
Three clones of pinot noir grapes, each with different cluster architectures, were inoculated with Botrytis spores at four growth stages, from bloom through veraison. This allowed us to determine both the critical time of infection and the interactive influence of bunch compaction. In subsequent experiments, individual berries were injected with spores at veraison, and vines were treated with urea thereafter, producing individual disease foci that allowed us to study the effects of cluster architecture and nitrogen nutrition on preharvest disease spread. We also investigated the effects of humidity, soil water, and nitrogen nutrition on the activation of latent infections. Additional experiments investigated the effects of fungicide timing on disease control.
Data showed that severe BBR results from significant disease spread before harvest, when the fruits are most susceptible. Most infections established at bloom remain latent and never cause disease; however, the few that do activate serve as primary infection foci from which secondary spread can occur. High soil moisture, high relative humidity, and high berry nitrogen content before harvest promote activation of latent infections. Tightly compressed clusters and high berry nitrogen content promote secondary spread. The necessary timing for fungicidal protection varies among years, depending on the occurrence of environmental conditions that cause latent infections, their activation, or secondary spread before harvest.
These results have resolved the two contradictory models of disease development by partitioning early and late-season infections into primary and secondary phases, respectively. The elucidation of several different factors involved in the activation of latent infections and secondary spread has provided a biological basis for better predicting when the disease will or will not occur. In turn, this knowledge will help to determine the proper time to apply fungicide. Results have been widely disseminated to growers in New York and the eastern U.S., and these results have shaped new disease control recommendations. The results have allowed grape growers to better time their fungicide sprays, resulting in fewer applications in some seasons and improved disease control in others. The overall effect of this research has been a decrease in pesticide inputs and an increase in profitability. Results were presented at a recent International Botrytis Symposium. Afterwards, I was invited by the world's leading authority on the disease to co-author a review article on the subject. This article will codify the new concepts of BBR development into the international literature.
- Federal Formula Funds - Research (e.g., Hatch, McIntire-Stennis, Animal Health)
- Private (e.g., commodity groups, foundations, companies)
- State or Municipal (e.g., NYSDAM)
- Other USDA (e.g., Water Quality, Special Grants, NRI)
- Department of Horticultural Science, Cornell University-Geneva
- Department of Plant Pathology, Pennsylvania State University
- Stella M. Zitter, Dept Plant Pathology, Cornell UniversityGeneva
- Robert M. Pool, Dept. Horticultural Science, Cornell University, Geneva
- Robert C. Seem, Dept Plant Pathology, Cornell University, Geneva
- James W. Travis, Dept. Plant Pathology, Pennsylvania State University