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Project description

The effects of vineyard cultural practices on grape mealybug and its natural enemies. (00FE004)
Program UC IPM competitive research grants program
Principal
investigator 		K.M. Daane, Insect Biology, UC Berkeley
Host/habitat Grapes
Pest Grape Mealybug Pseudococcus maritimus
Discipline Entomology
Review
panel 		Applied Field Ecology
 Start year (duration)  2000 (One Year)
Objectives Determine the effect of vineyard management practices (nitrogen fertilization, girdling and gibberellic acid on grape mealybug pest status and biology.

End-year
progress 		Mealybug pest damage in vineyards has proved difficult to accurately predict. The grape mealybug, Pseudococcus maritimus, is the primary mealybug pest of Central Valley table grapes. Growers and PCAs have suggested that vigorous vine growth (e.g., fertilization) and berry sizing practices (e.g., girdling and gibberellic acid) are often associated with mealybug pest problems. In 2000, we tested these relationships in an experimental vineyard and greenhouse. In a Thompson seedless (cv.) vineyard, six nitrogen treatment levels (0, 25, 50, 100, 200, and 400 lbs N/acre) have been maintained since 1993. In this experimental block, we followed mealybug and parasitoid populations and compared mealybug density, size and fecundity with fertilization treatments, N petiole content, cane growth and pruning weights. This work was repeated in the greenhouse, using potted Thompson seedless plants that were provided with the same N fertilization levels as the field trial. Again, mealybug growth parameters were measured. Results from the field trial showed no difference between fertilization treatments or berry sizing practices in mealybug density or egg deposition. However, these results may have been influenced by the activity of natural enemies, which dramatically lowered mealybug densities. In contrast, the more controlled work conducted in greenhouse trials showed mealybug densities and egg deposition was higher in treatments with higher fertilization. We conclude that more vigorously growing vines can increase mealybug pest status. There is less evidence that berry sizing practices have any influence on mealybug pest densities.

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