Evaluation of Microsprayers for Frost Protection in California Vineyards

The experimental site was a Chardonnay vineyard located near Los Alamos, CA. Plots were established during early March 1993 and data were collected from March 11, 1993 through May 20, 1993 and March 14, 1994 through May 23, 1994. The microsprayer (Wade Pulsator?) under evaluation uses a pulsing action that produces larger diameter droplet sizes, while maintaining lower application rates as compared to those found with conventional microsprayer design. This microsprayer produces a narrow band of water (approximately 24 inches wide) directed over the cordon of the vine. Microsprayers were installed in every vine row and mounted 22 inches above the cordon on every other stake, approximately 10.5 feet apart. A five acre block of microsprayers was compared to an adjacent sprinkler block. The sprinkler block had a typical design and installation for commercial coastal vineyards. Sprinkler spacing was 50.0 feet X 42.0 feet, using a conventional impact type head and a 7/64 inch nozzle. The water source for both systems was an above ground reservoir filled by pumping ground water. Water was passed through a perforated tube filter for the sprinklers and a sand-media filter for the microsprayer system. Water use was measured by a Rockwell sealed register meter. Data collected for the microsprayer and sprinkler blocks were bud temperature, air temperature, and relative humidity. Air temperature was also recorded at 18 inches from the cordon and the middle of the vine row (at cordon height). Environmental conditions monitored outside the vineyard were air temperature, wind speed and direction, and relative humidity. Environmental data were collected with Omnidata data loggers using a series of thermocouples for bud temperatures (attached at bud locations) and Physchem RH sensors’for air temperature and relative humidity. A data logger and associated sensors were located within the microsprayer and sprinkler blocks and outside the vineyard. Due to the low number of spring freezing events in 1993 and 1994, data collection was limited at the vineyard site. During the spring freezing events which were monitored, microsprayers provided a level of frost protection which was similar to that provided by sprinklers. Also, the use of microsprayers resulted in a savings in water use of approximately 80 percent during selected freezing events. This was a preliminary experiment and further research is needed before general recommendations can be given. Continuing studies will include a series of tests under controlled freezing conditions in a cold chamber.