Cultural Practices for Integrating Arthropod Pest management with Improvements in Grape and Wine Quality
Research has shown leafhoppers (Erythroneura spp.) to be sensitive to vine water stress: Leafhopper adults lay fewer eggs on grape leaves and leafhopper nymphs have higher mortality. In our previous studies we have found second generation leafhopper nymphs to be dramatically lower under a mid-season deficit irrigation regime. In addition, vine water stress, either just prior to harvest, or more recently, mid-season, has been used to improve the color and flavor of wine. The aim of our study is to use one vineyard cultural practice, i.e., timely deficit irrigation, to achieve several goals: 1) Decrease density of leafhoppers 2) Improve quality of winegrapes and 3) Make more efficient use of water. We set up an experiment in a Paso Robles vineyard to compare two deficit irrigation treatments to the grower?s standard irrigation practice, which was to irrigate as close to the full evapotranspirative needs of the vineyard as possible (i.e., 1.0 ETc). One of our treatments was to reduce that to 50%(i.e., 0.5 ETc) between berry set and veraison and the other was to reduce that to 25%(i.e., 0.25 ETc) between berry set and veraison. The actual deficit irrigation period was between June 6 and August 20. Leafhopper numbers early in the season were quite high, and a communication error with the spray crew did not protect our study site from being treated with an insecticide, and we therefore lost the leafhopper data for the 2001 season. We estimated vine water stress by taking measurements of leaf water potential every week. Water stress did not show up until 4 weeks after the deficit irrigation treatments were initiated, and for the next six weeks, water stress was about 5%higher under the deficit irrigation treatments, but there was no stress difference between 0.5 ETc and 0.25 ETc. We also made weekly measurements of stomatal conductance, which is a measure of the leaf gas (CO2 and water) exchange rate (measured in mol m-2 s-1). Stomatal conductance was about 40%higher in the 1.0 ETc treatment than the deficit treatments for the entire period measured, but again, there was no difference between 0.5 ETc and 0.25 ETc. At harvest, we took berry samples and analyzed them for sugar (°Brix), size (berry weight) and color (skin extraction), and we took yield samples in each treatment. Yield was about 25%lower in the deficit irrigation treatments compared to 1.0 ETo, and again, there was no difference between the 0.5 ETc and 0.25 ETc.treatments. Neither °Brix nor berry weight differed among any of the treatments. Color intensity of the skin extraction was highest in 0.50 ETc, and significantly different from 1.0 ETc, but not 0.25 ETc In winter we took pruning weights as a measure of vine vigor. Compared to 1.0 ETc, vigor declined by about 30%in the 0.25 ETc treatment, but no significant difference was detected in the 0.50 ETc treatment.
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