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Project description

The Effects of Vineyard Cultural Practices on Grape Mealybug and its Natural Enemies. (98FE027)
Program UC IPM competitive research grants program
Principal
investigator 		K.M. Daane, Biological Control, Environmental Science Policy and Management, UC Berkeley/Kearney Agricultural Center
Host/habitat Grapes
Pest Grape Mealybug Pseudococcus maritimus
Discipline Entomology
Review
panel 		Applied Field Ecology
 Start year (duration)  1998 (Two Years)
Objectives Develop a research-oriented sampling program for grape mealybug that shows pest abundance, development and seasonal movement on different parts of the vine.

Determine the effect of cultural practices on grape mealybug ecology, including: pest status, growth parameters, and natural enemy abundance and species composition.

End-year
progress 		Mealybug pests in vineyards have proved very difficult to accurately sample. In 1999, we completed studies of mealybug abundance and distribution throughout the vine, which where compared with different sampling methods. Our results suggest that timed field counts by experienced samplers (5 minutes per vine) and 3-spur field counts of mealybugs (2 minutes per vine) at midseason are the most promising sampling methods. The distribution study also confirmed that most mealybugs are found under the bark or in other concealed locations; therefore, any effective treatment of natural enemy must be able to penetrate the bark. Further, grape bunches toughing old wood (e.g., trunk) had significantly higher mealybug damage, suggesting that separating bunches from bark early in the season could reduce damage. Also, because the majority of mealybugs remained in hidden locations until July (2nd generation of eggs hatch), we predicted that blocking mealybug movement to the bunches could lower damage at harvest. We tested this by applying a sticky barrier between the grape bunches and canes at midseason, and found that mealybug damage was reduced by 50%.

We also examined the role of management practices on mealybug density, specifically - nitrogen (N) fertilization and trellis systems. We found weak effects of N on mealybugs growth parameters. Similarly, we found little or no effect of trellis systems on mealybug density or damage. More research is warranted. To better understand the wide range of cultural factors that could affect mealybug infestations, we developed and distributed a survey to 424 table grape growers. Growers reported that one popular grape variety -Ruby Seedless-is more likely than others to experience serious mealybug damage. They reported no differences in mealybug damage among various irrigation and trellising systems, although growers that used the pesticide Lannate, (methomyl) reported higher damage-which could be a statistical artifact, but could also indicate that this material is not effective or is disruptive to natural controls.

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