Bloom and post-bloom are critical times for disease management in grapes. Temperatures and rainfall are generally favorable for pathogen development at this time, though conditions are not as wet as those observed last year. This is particularly true for grapes that are susceptible to powdery/downy mildews and Botrytis. The fruit are generally more susceptible to infection during bloom and shortly after. Make sure that you apply highly active materials during bloom and post-bloom for control of these pathogens. If you observe Botrytis following bloom, work with your local county agent to develop a fungicide resistance profile for your location — determine which fungicide classes still work at your location. By now, for most locations in Georgia where strobilurin fungicides (e.g. Abound, Pristine, etc.) have been utilized, activity is likely minimal to nonexistent for this class of chemistry for any or all of these pathogens. If using any strobilurin, tank mix with other fungicides with activity against these pathogens and others. See my previous post (6 April; Fungicide Suggestions for the Year) for suggested fungicides for this timeframe and as we progress through the season.
