In the two-year study, from 2021-22, the researchers tested the effects of different types of berry damage in the presence or absence of adult D. melanogaster on a sour rot-susceptible Vignole cultivar in fields at Cornell AgriTech in Geneva, New York. Berry clusters were inoculated with yeast and sour rot bacteria.
In both years, they found, sour rot was most severe (measured by the percentage of infected berries in a cluster) on mechanically injured clusters – to mimic bird pecks – compared with other treatments. When fruit flies were present, it was worse. They discovered a similar pattern when berries were damaged by yellowjackets, though the presence of fruit flies increased infections only in the second year.
In a third damage treatment, damage by grape berry moth larvae had minimal effect on sour rot severity, except in the presence of D. melanogaster in 2022.
“We’ll use this knowledge to help make recommendations to growers about how to try to control this type of cluster rot,” Loeb said.
One such recommendation is to use bird netting and selectively apply insecticides to deter insects and limit berry damage in the latter part of the growing season, Loeb said.
Though insecticides are known to work well for fruit flies, they come with costs.
“We now know there is a considerable amount of insecticide resistance developing in fruit flies in New York and around the country,” Loeb said. “So that’s another part of this. We now understand what the risk factors are and when it makes sense for growers to apply insecticides and other kinds of microbicides.”
Growers may apply treatments when extended wet weather creates cracks in berries, for example. Experiments are also underway to develop nets with small mesh to protect the berries from yellowjackets.
“It’d be nice to get to a place where we can develop risk models that growers can use to help them make [treatment] decisions,” Loeb said.
Co-authors include Katie Gold, assistant professor, and a Susan Eckert Lynch Faculty Fellow in the School of Integrative Plant Science Plant Pathology and Plant-Microbe Biology Section; Stephen Hessler, research support specialist in the Department of Entomology; and David Combs, research support specialist in the Plant Pathology and Plant-Microbe Biology Section; all at Cornell AgriTech.
The study was funded by the New York Wine and Grape Foundation and the United States Department of Agriculture.
Source : cornell.edu