Friday, September 30, 2011

Vine Covers for Table Grapes

Table grapes are a labor and material intensive crop; annual operating expenses may exceed $7,000 per acre. Thus, it is critically important for growers to protect late season grapes from rain, as exposure to precipitation within six weeks of harvest can stimulate the development of rots and molds that may render them unmarketable. Rain damage may be avoided by harvesting the fruit before the fall rainy season, but the grapes of some late maturing varieties may not ripen by then, and the price paid for grapes often increases towards the end of the season, thus providing an incentive to harvest fruit as late as possible.
Thus, many growers with late-season table grapes cover their vines with sheets of plastic film, beginning in late August or early September. At least two different colors of film, green and white, are
available, but data to distinguish the potential differences the two films might have on vine physiology or fruit quality are not available.  The cost to procure, install, and remove the films is very expensive, so growers need objective information on film performance.  To provide such information, we have just begun a study to determine how the two most common film covers may affect canopy microclimate, vine physiology, and fruit quality, to help optimize the productivity and quality of late-season table grapes in California.  Follow the blog and we'll update you periodically on our findings.
Different vine covers being evaluated in a commercial vineyard near Fresno, CA.

Soon after installing the covers, noticeable changes in canopy microclimate were observed, including higher temperatures, and condensation was evident on the inside of the covers.

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