Scouting at the West Madison Research Station (WMARS) vineyard on 7/2/19 showed an increase in the number of phylloxera galls (Figure 1) observed on most cultivars. To assess grape phylloxera incidence, we check 30 leaves per plant and count the number of leaves with galls. Incidence varied from 0% to 67% on 7/2/19 with the first signs of leaves starting to fold over due to the high number of galls starting to show (Figure 2).
Control: Assail, Danitol, and Movento are registered to control grape phylloxera. However, these work best pre-bloom, when phylloxera nymphs from the first generation are exposed while climbing to the new foliage at the shoot terminals. Once grapes have reached the bunch closing stage, it is not recommended to spray for phylloxera any longer. If you notice an infestation on any of your vines past the bunch closing stage, you should carefully monitor for the first signs of gall formation early next spring and consider using Admire Pro as a prophylactic soil-drench. Admire Pro should be applied from bud swell until the first leaf is fully expanded, in areas which have shown high phylloxera infestations the previous summer.
Scouting in Door County at PARS shows that a few grape flea beetle larvae and a few grape plume moth larvae remain feeding on leaves but as mentioned in previous issues will not cause any economic damage on grape.
Last week, I received a picture from a Wisconsin grape grower of what looks like cottony grape scale (Figure 3). This is the first time these are brought to my attention on grape plants in Wisconsin though this insect is common in the North East, Pacific Northwest, and Canada, and likely in the Midwest too. Should you observe these scales on your grape plants, please let me know at email@example.com. At this point, I don’t believe these will have an impact on our grapes, but we should keep an eye out for these as they can reduce plant vigor and vector diseases such as grapevine leafroll virus.
Thanks to Andi Nelson and Annie Deutsch for scouting at the research stations. Happy growing season!This article was posted in Grapes and tagged Grapes, Phylloxera.