Optimal Management of Lepidopteran Pests of Grapes

The primary objectives of this research project are: 1) To evaluate and refine monitoring programs for western grapeleaf skeletonizer (WGLS) and omnivorous leafroller (OLR) in grapes, and 2) To determine spatial and temporal patterns of WGLS and OLR distribution in order to develop a non-preventive, true IPM program for dealing with these two serious vineyard pests. Several significant results have already been produced during the two years of this project (1992, 1993). Sex pheromone bucket traps with insecticide strips caught more WGLS moths at peak flight than did traps with ethylene glycol. OLR bucket traps with insecticide strips were somewhat more efficient than sticky bottom pheromone traps. With respect to monitoring OLR larvae, the UC-recommended bunch count technique (developed mostly on Thompson seedless), appeared to have questionable applicability for detecting OLR in tight-clustered grape cultivars (e.g., Barbera). Thus, early season OLR infestations, readily evident before berry sizing in such cultivars, later became “invisible” as the clusters developed. Generally low population levels of both WGLS and OLR during 1993 made collection of sufficient numbers in field trials a major challenge. A study comparing releases of Trichogramma parasiotoids and applications of Bacillus thuringiensis microbial insecticide against OLR which involved careful examination of 600 clusters at harvest produced only 4 OLR larvae and 5 OLR pupae. However, these same counts also revealed from 1 to 6 clubionid spiders (prob. Chiracanthium inclusum) in each grape cluster, suggesting that these predators may have been a factor in the low OLR numbers. For all the commercial vineyard blocks which were sampled in 1992 and 1993, the growers felt that chemical control was unnecessary, based on the pest monitoring data which we compiled. Thus, we have clearly demonstrated that preventive treatment for these lepidopteran pests of grapes is by no means an essential activity in San Joaquin Valley vineyards.