Wendy McFadden-Smith Tender Fruit & Grape IPM Specialist and Kevin Ker, KCMS Inc.
This is the season for unsettled and, in some cases, severe weather accompanied by hail. The most common issue for vineyards is fruit injury and the development of Botrytis. The infections are not the result of new infections, but rather the activation of symptomless infections that occurred at bloom. The Botrytis fungicides applied at cluster closure will penetrate the berries and inactivate those infections. All of the Botrytis fungicides (Vangard, Scala, Switch, Elevate, Rovral) are equally effective and have protective, post-infection and anti-sporulant activity. Rovral cannot be applied later than bunch closure so if you are planning to use it this year and haven’t already done so, now is the time. Bayer recommends using Scala at veraison but it can be used within 7 days of harvest. Keep in mind that you should not use any Botrytis fungicide family in two consecutive sprays and that Vangard, Scala and Switch all contain Group 9 fungicides. You have to plan your botrytis control program in advance to make sure you can make maximum use of the products available.
If more than 60% of the clusters in your vineyard have sustained injury and shoot damage is easily visible, all of the crop should be dropped to reduce plant stress. Prune back injured shoots to promote the development of laterals close to the head of the vine. This will result in the production of healthy, fruitful canes for next year. Continue to protect the foliage and shoots for powdery and downy mildew for the rest of the season to promote healthy shoot growth to survive the upcoming winter.