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Project description

Pruning for Control of Pierce's Disease. (98FE032)
Program UC IPM competitive research grants program
A.H. Purcell, Environmental Science, Policy and Management, UC Berkeley
Host/habitat Grapes
Pest Pierce's Disease Xylella fastidiosa
Disciplines Entomology, Plant Pathology
Applied Field Ecology
Start year (duration)  1998 (Two Years)
Objectives Determine if pruning can eliminate Pierce’s disease from grapevines with symptoms of the disease.
Severe pruning (just above the graft union) in the winter of 1998-99 successfully regenerated healthy grapevines from trellised vines in Napa Valley that had severe symptoms of Pierce's disease during fall, 1998. Grape varieties used were Cabernet Sauvignon, Merlot, Pinot noir, Chardonnay, and Cabernet franc. Vine ages were from 2 to over 8 years. Recovery rates ranged from 87 to 100%) for vines with the least severe symptoms; from 71 to 95% for vines in the "moderate" severity category; and from 38 to 85% for the most severe category. For the least severe disease category, rates of recovery for pruned vines were not substantially or significantly greater than normal dormant pruning in some plots. Visual ratings of Pierce's disease agreed with results from using a sensitive molecular diagnostic test (Polymerase Chain Reaction) for Pierce's disease for 79% of the least severe category, 80% of the moderate category, and 97% of the severe category. The results demonstrated that it is feasible to regenerate healthy vines from vines with Pierce's disease more quickly by severe pruning than by pulling and replanting the vines. The experimental results suggest that only vines with symptoms near the base of the cane should be severely pruned in order to regenerate a healthy vine. Further research is needed to validate the effectiveness of severe pruning in different viticultural regions and to test the effectiveness of selective pruning of laterals (e.g., cordons) rather than the trunk of the vine.

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