Search NC Small Fruit, Specialty Crop, and Tobacco IPM

Wednesday, July 7, 2010

Vineyard heat and drought stress alert

Developing grapes at Westbend Vineyards, Lewisville, NC. Photo: HJB

Dr. Sara Spayd, professor of viticulture in the NC State Horticulture Department, is warning of heat and drought stress in NC vineyards. The record heat this week has the potential to impact not only people but plants as well. See here to read Dr. Spayd's complete alert.

Right now, fruit quality and yield is of primary concern, but heat and drought stress can also have implications for insect management. Numerous wood boring beetles can attack grape vines in NC. Most wood boring beetles will not kill an infested vine outright and are rather a symptom of a larger problem weakening the plant. Drought stress is often the initial problem responsible for weakening vines.

In fall 2007, I visited a small vineyard that was planted in half Chardonnay and half Merlot. The Chardonnay vines were small but generally healthy. The Merlot vines, however, were virtually all dead or dying and riddled with several species of wood boring beetles.

Merlot vines and canes with extensive wood boring beetle damage (indicated by arrows). These perfectly round holes are adult beetle exit holes. Some larvae were still present in these vines as well. Photo: HJB

Wood boring beetle larvae collected from Merlot vines. The lower larva is likely that of a long horned beetle (Coleoptera: Cerambycidae) and the insects in the upper image are likely shot hole borer larvae (Coleoptera: Scolytidae). Photo: HJB

According to Dr. Spayd, Merlot is often the "canary in the coal mine" for drought stress. At this vineyard, neither variety had been irrigated the preceding summer, but the Chardonnay vines tolerated the stress better. Numerous beetles were attracted to the stressed Merlot vines and were the final straw that pushed them over the edge. Water is an important part of woody plants defenses against boring beetles. If there are only a few larvae in a tree or vine, the plant will use sap to flood them out. Water stressed plants are no longer able to mount this defense and can be taken over by beetles.

Cultural control is the best method of wood boring beetle management. Healthy vines will seldom host damage beetle populations. Any tissue that is infested with beetle should be removed during winter pruning and destroyed. If cuttings are left in the vineyard, beetles may be able to complete their development and re-infest vines the following spring. Chemical control is recommended. Chemicals will not effectively treat larvae inside vines, and targeting adults is difficult due to their high mobility and the large number of species potentially present.

One beetle is an exception to the rule in that it will attack healthy vines as well as weak vines. The granulated (formerly Asian) ambrosia beetle can potentially damage healthy vines. Granulated ambrosia beetle is a serious problem in nursery production, but does not appear to be widespread in NC vineyards at this time.

More information
Vineyard Alert: Extreme Heat and Droughty Conditions Affecting NC Vines
Granulated ambrosia beetle in NC

No comments: