If you don’t detect vine mealybug (VMB) infestations by harvest, your grape picking crew or processor will. Although there is nothing that can be done to reduce infestation at that time, knowing the specific areas in the vineyard that are infested is important in managing the pest over seasons.
First, a brief description of what your grape harvesters will find. The upper canopy may not show much sign of infestation. However, the crown of the plant will be covered with sticky, drip- ping honeydew that extends down the trunk.
The vine will also look as if oil were dripped onto the crown. The clusters in the immediate area will be covered with the sticky, syrup-like material. Mealybug body parts and, especially, egg cases and crawlers will be found throughout the clusters. This sort of infestation should not be mistakenly attributed to grape mealybug.
Grape mealybug will not produce such levels of honeydew. Vines where these symptoms are found should be flagged.
Either the harvest crew or an individual assigned to walk the vineyard can identify and mark infested vines. There are a number of good publications that show what to look for. One of the best is entitled Vine Mealybug: What You Should Know, UC publications 8152. It is available at your local Farm Advisor Office.
If the infestation is new, a post harvest application should be made. The treatment should be made prior to mid November. Guidelines for treatment can be found in UC ANR publication 3448 entitled UC IPM Guidelines for Grapes.
Information can also be found at http://www.ipm.ucdavis.edu/. The post harvest application is critical in preventing the spread of VMB via wind-blown l eaves.
The vines flagged at harvest should be examined in the spring (early March) for both survival of mealybugs sprayed post harvest and for timing spring applications. Survey the base of spurs near the crown of the vine. Use a magnifying glass to identify the small crawlers that are migrating up the vine.
Spring applications should be made when air temperature is above 60 F. Warmer temperatures encourage VMB activity and they will quickly disperse throughout the vine. Cool temperatures (below 60 F) impede movement and, consequently, exposure to insecticides.
You will save yourself a lot of time by looking at vines that were known to be infested the previous year. The next critical period for finding VMB is mid May.
Survey previously infested vines and look for VMB crawlers on basal leaves. They will feel tacky or sticky, which is an indication they are beginning to feed. As soon as crawlers are found on leaves, an application should be made to keep them from establishing on fruit and foliage.
Infestations on the trunk will display new honeydew secretions as described above. Also, ants will be quite active. Following their activity on the vine will eventually lead to mealybugs hidden under bark.
The approach we have outlined above may appear excessive and costly, but experience has shown it is not overkill. Following these steps will help restrict spread in your vineyard as well as slow population growth.
In subsequent years a reduced spray approach may be warranted for vineyards producing raisin or wine grapes. Vine mealybug infestations are spreading rapidly in the San Joaquin Valley.
What has been both surprising and disappointing has been the lack of awareness about this destructive pest. Growers should have crews trained to identify early VMB infestations in order to limit cost of season-to-season management and contaminated fruit. Visit your local UC Cooperative Extension office for the most recent information.