Seasonal biology of the Gill’s mealybug, Ferrisia gilli, in foothill vineyards

The seasonal biology of Gill’s mealybug, Ferrisia gilli, a new mealybug pest of grapes grown in the California Sierra foothills, was studied in five commercial vineyards located in El Dorado County during 2008. In each vineyard, untreated and treated vines were monitored bi-weekly by searching vine sections or the entire vine during timed searches and recording Gill’s mealybug life stage and numbers. Mealybug mummies were collected and held for parasitoid emergence and observations of predators in the field were recorded. Vineyard cooperators were kept apprised of the mealybug location and life stage and this information was used to time mealybug treatments, mostly consisting of applications of buprofezin and/or acetamiprid. Just prior to harvest, two hundred clusters were rated on a scale of 0 (no mealybugs present) to 3 (unacceptable damage) and the number of mealybugs found in fifty clusters was counted.

Specific accomplishments (2008):

1. Tracking of Gill’s mealybug life stages during the season helped us determine it completed 2 full generations during the 2008 season.
2. Early in the season Gill’s mealybug is best found on old and new spurs. This is important for monitoring and making insecticide treatment decisions in June. Observations showed that honeydew production does not generally take place until towards harvest, and is not a good clue to finding Gill’s early in the season.
3. Treatments timed for the crawler/nymph stage out on leaves were targeted for late June, about a week earlier than previously targeted. Growers with neighboring blocks were well coordinated in their spray control program due to information and communication generated from this study.
4. Cluster damage ratings showed that this pest appears similar to grape mealybug-if left untreated it can build to undesirable damage. We observed up to 42%of the clusters in untreated plots had Gill’smealybug, and 11%of these were rated either a “2” (more than ten mealybugs) or “3” (unacceptable damage).
5. Insecticide treatments such as buprofezin (Applaud) and acetamiprid (Assail) appeared effective; however this combination is not desirable for a long term management plan due to effects of insecticide resistance and potential detriment to natural enemy populations.
6. Parasitized Gill’s mealybugs were found at every site, however, numbers of mummies were very low in treated plots and only a few Acerophagus were reared out of collected mummies.
7. Gill’s mealybug continues to be found at vineyards in the area. We now estimate at least 270 acres of grapes have the Gill’s mealybug in a portion of the vineyard.
8. Our outreach strategy is to 1.) Communicate our monitoring information from this study to growers in order to properly time and increase the efficacy of their treatments and to 2.) Inform the greater extension, Pest Control Advisor, and research community in order to build awareness of Gill’s mealybug as an emerging pest in grapes. Several grower meetings, one popular press article (CAPCA Adviser magazine), one peer reviewed article (California Agriculture magazine), and a research presentation (Entomological Society of America) have been generated from this research thus far.