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Sunlight Enhances Fungal Disease Control Trials in New York and Washington show positive effects of UV radiation and warming of canopy By Wayne F. Wilcox and Craig N. Austin U nlike the general public, grapegrowers know that disease management does not involve a choice between "chemical" and "non-chemical" approaches, but rather an informed integration of those components to fit each individual's needs and philoso- phies. This article's focus is the new infor- mation pertaining to a non-chemical tool for the vineyard, specifically the dramatic effect that sunlight has reducing powdery mildew development—and its implications with respect to disease management. A subsequent article will review some of the new fungicides now available to help growers control both powdery mildew and downy mildew. Sunlight exposure and powdery mildew Growers have long observed that powdery mildew (PM) is most severe in shaded areas of vineyards, but the causes and actual impact of the phenomenon have been poorly understood. We recently completed a five-year study to determine the impact sunlight exposure has on powdery mildew development, which has shown that growers can greatly enhance their disease manage- ment programs simply by using common canopy management practices to optimize light interception throughout the canopy and fruiting zone. An early experiment was conducted in a Chardonnay vineyard near Dresden, N.Y., where a small portion of the easternmost row was bordered by a group of 50-foot pine trees. Despite a spray program that controlled PM adequately on nearly all other vines, we had seen that this disease com- pletely destroyed the clusters on the three panels of vines immediately next to the trees, although these panels were sprayed exactly the same. These panels were shaded Wine East HIGHLIGHTS: • • sunlight can dramatically reduce powdery mildew development. in a trial, the disease became eight to 40 times more severe on the most heavily shaded leaves compared to the leaves most exposed to sun. • When improved spray coverage is factored in, the benefit of opening up canopies for powdery mildew control is compounded and extends to other diseases. during the morning, and it wasn't until the sun crested over the treetops just before noon each day that the vines received their first direct exposure to sunlight. The next year, we initiated a trial in which we inoculated leaves on either the outer (exposed) or inner (shaded) portions of vines, which were located either im- mediately next to or 200 feet away from these trees, thereby providing a total of four levels of natural shade. The resulting disease severity increased substantially with each increasing level of shade, becoming eight to 40 times more severe on the most heavily shaded leaves (interior vines next to the trees) compared to the sunniest leaves (exterior vines away from the trees). (See Figure 1 on page 52.) Although shading could potentially change air temperature or relative humidity within the vine canopy, our measurements did not show this. However, they did show that UV radiation levels and leaf tempera- tures were dramatically different among the different treatments. As one would expect, within the shaded regions UV levels were a mere fraction of those in the sun, and Winegrape growers should hit the powdery mildew fungus during the first few weeks following the start of bloom rather than wait until damage has occurred. WineEast WinePkgingNaylor_Dir11.qxp 11/24/10 4 Wine Packaging by Naylor Naylor is the premier supplier to over 2000 wineries, wine shops and distributors in the US and Ca. WPN's products are biodegradable and recyclable.Our shipping boxes have been approved by Fed Ex & UPS and our in-stock items include wine carriers, gift boxes and wine shippers.Our design team can assist you with specialized packaging and custom imprinting. www.naylorpackaging.com (800) 292-3370 or (717) 993-2431 Fax (717) 993-9460 4138 Vineyard Rd. Stewartstown, PA 17363 sales@naylorwine.com is a lifetime member of Wine America and the PA Wine Association. a winery for over thirty-five years & Naylor Wine Cellars has been Wines & Vines MARCH 2011 51