Thrips are small yellowish-brown insects, approximately 0.04 inch long, with feathery wings. Thrips are generally not a problem for wine grapes, but both western flower thrips and grape thrips are known to cause damage on grapes. Western flower thrips are nearly ubiquitous in the environment, feeding on numerous different hosts, and as their name implies, are particularly fond of flowering plants. In grapes, their populations peak in May, coinciding with grape bloom. Grape thrips also feed on a variety of hosts, including grapes, but populations usually greater later in the season, coinciding with peak vine growth and fruit development.
What we are concerned with right now is damage to blooms due to western flower thrips. Several growers in West Georgia have observed browning and dying of the blooms on Blanc du Bois vines specifically. Phil Brannen has found that Cladosporium and yeast are associated with the damaged blooms, but it is likely that these pathogens are secondary to initial injury due to thrips feeding.
We are not sure if only Blanc du Bois vines are impacted by thrips, but those are the only examples of issues that we have seen thus far. Also, please don’t freak out (yet), thrips are VERY common in the landscape and just because you may find them on your grapes doesn’t mean they are actually causing damage. So, if you believe you are having issues with your blooms, please contact your local agent.
Thankfully, if thrips are an issue, we have several chemical options to help manage them. Please see the table below. Note that since there are likely blooms still in the vineyard and flowering weeds, to protect bees, it is advised to apply these insecticides during late evening, night, or early morning when the bees are not present.
One additional note about thrips management in vineyards. Western flower thrips are attracted to flowers, and flowering weeds under the vines and/or within the row middles can provide resources for thrips. These weeds can attract thrips in to the vineyard, build up populations on the weeds and then move up into the grapes. Good weed control is essential, particularly near grape bloom when the grapes are most vulnerable to western flower thrips. Note, though, that if flowering weeds are present within the vineyard during grape bloom, herbicide or mowing the weeds could force the thrips to move into the grapes. Thus, pre-bloom weed management for thrips suppression is ideal.
If you have any questions or concerns, please let someone from the grape team know.