INFLUENCE OF LOBESIA-BOTRANA LARVAE ON FIELD SEVERITY OF BOTRYTIS ROT OF GRAPE BERRIES

A 3-yr study was conducted in the vineyards of Bordeaux to assess the effects of the last two generations of Lobesia botrana larvae on the development of Botrytis rot. In the absence of fungicides to control B. cinerea, second-generation larvae favored the initiation of Botrytis rot on grapes in midseason (i.e., at the beginning of veraison). At this point, the number of second-generation larvae per cluster was highly correlated with the number of early disease centers. At harvest, the effect of second-generation larvae alone was also measurable and resulted in a significant increase in disease severity. In 1989, this effect was detected on the cultivar Merlot at an infestation level of eight larvae per 100 clusters. For the third-generation larvae, significant increases in rot severity at maturity were caused by infestation levels of eight and 12 larvae per 100 clusters on Merlot and Sauvignon, respectively. The cumulative damage caused by the larvae of the last two generations appeared to result in higher Botrytis rot severity. The effects of larvae on disease severity varied with year and cultivar. The potential of these biological thresholds for use by growers is discussed. A method for artificially infesting vineyards with laboratory-grown pupae was also studied.