Plant pathologist and viticulturist Dr Megan Hall joined me recently to share her expertise and insight on sour rot disease in winegrapes. In today’s blog, we discuss 3 prevention and control strategies to combat sour rot in the vineyard through cultural practices and proper spray practices.
Proper Variety Selection
Be mindful of the varieties you are planting and the characteristics of your site. If your climate is already more prone to sour rot (damp and warm near harvest, for instance), you can opt to plant looser cluster varieties which are less susceptible to sour rot. Varitest like Vignoles have classically compact clusters that cannot be loosened and therefore will be much more susceptible to sour rot and harder for sprays to effectively penetrate.
Of the three causal organisms of sour rot – acetic acid bacteria, yeast, and fruit flies – the main thing that growers can influence are fruit flies. And, fruit flies do not like open air environments. They like being cozy and under leaf cover, so your biggest tool to combat them is to open up the canopy by:
- Early and sometimes late season leaf removal
- Reducing cluster compactness
- Reducing clusters from pushing up against each other
- Removing leaf layers to lower the humidity in the canopy
Dr. Hall’s extensive research on sour rot showed that spraying a combination of an antimicrobial and an insecticide starting at 15 brix and before symptoms develop can significantly reduce the incidence of the disease for blocks where sour rot was an issue the prior season.
If sprays were applied after symptoms developed, no better control of the disease resulted. Getting control of sour rot once symptoms are noticeable is nearly impossible, and your best hope at that point is for the sprays to prevent the percentage of infection from increasing in the block.
Note: As with most sprays, over-spraying for sour rot can result in resistance, leading to a more significant problem in the long run. It’s crucial to rotate through different modes of action groups when it comes to insecticides and not to spray excessively.
If you want to learn more about preventing and combating sour rot, check out https://www.vineyardundergroundpodcast.com/vu026.