As vines enter veraison, there is a shift in resource (nutrients, carbon) allocation from the canopy toward the ripening fruit. The result is can be a manifestation of nutritional and systemic disease (viral, bacterial) symptoms in canopies of deficient and/or infected vines. Please be on the look out for symptomatic vines as you scout your vineyard this post-veraison season. Objective diagnoses can only be made by lab-based testing. Visual diagnoses, however, can go a long way in helping to determine appropriate actions. When in doubt, contact your local county ANR extension agent. Here is an extension publication on “Red Leaves in the Vineyard” from colleagues at Rutgers University: https://njaes.rutgers.edu/fs1260/. The publication contains a flowchart to follow when observing red leaves in the vineyard, which can be caused by both nutritional deficiencies as well as systemic disease infections.
In light of this, we just published an extension bulletin on Grapevine Pierce’s disease (PD) that may be of interest to some of our blog subscribers. PD was observed in several north Georgia vineyards last year; let’s hope we see lower incidence during the 2019 post-veraison season. PD symptoms can be visualized primarily throughout August and September in southeastern US vineyards. Please see the Grapevine Pierce’s disease publication here: https://extension.uga.edu/publications/detail.html?number=B1514
Last, our vineyard management poster, now available in both English (https://extension.uga.edu/publications/detail.html?number=C1151) and Spanish (https://extension.uga.edu/publications/detail.html?number=C1151-sp) languages, has a “scouting” comment in the “cultural practice” section during pre-harvest. There are several other disease and insects also worth scouting for throughout post-veraison that are also mentioned on this poster. These posters can be obtained at regional vineyard meetings or from your local county ANR extension agent.
In closing – please scout your vineyard for symptomatic vines throughout the ripening period and act accordingly. Please let any of the UGA Extension Viticulture Team members know if you have any questions or concerns, and please start with your local county extension ANR agent.