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86 WINES&VINES April 2018 GRAPEGROWING WINE EAST Among the systemic insecticides, spirotet- ramat appeared to outperform acetamiprid and helped slow the spread of GLRD. 16 Once a block has been identified as positive for GLRD, it will be important to minimize populations of the potential vectors to reduce spread within the block and to adjacent blocks. Scouting for mealybugs in vineyards with GLRD can be important to reducing its spread. Unfortunately, to our knowledge, recom- mendations regarding insecticide spray pro- grams for slowing the spread of GLRD have not yet been optimized. Insect vectors can also "hitchhike" from infected areas to clean areas or blocks via human activity (by vineyard workers and equipment), suggesting appro- priate measures be taken to minimize this method of spread. 12 Lastly, a study with grape phylloxera (Da- ktulosphaira vitifoliae), a phloem feeder and potential vector of these viruses, showed that phylloxera can acquire GLRaVs in greenhouse transmission experiments, but this was not observed in the field. However, there was no evidence that phylloxera can transmit GLRaV- 1, 2, 3, or 4 to healthy vines. 20 Surveys for the presence of GLRaVs Interest in GLRD and the extent of its effects has been growing in the northeastern U.S. and Canada over the past 20 years. This concern has resulted in a number of surveys in some prominent grapegrowing states that have con- firmed the presence of GLRaVs in commercial vineyards and yielded important information necessary to the management of grapevine leafroll disease. As a result, academic institu- tions have developed research programs around this important group of pathogens and created a growing body of information that will be essential for vineyard managers. For example, surveys conducted in New York, Ohio and Virginia have revealed the pres- ence of GLRaVs in commercial vineyards in those states. 5, 8, 9 However, no extensive surveys have been conducted in Pennsylvania vine- yards. Based on the fact that some Pennsylva- nia vines were found infected by GLRaVs, 6 and that GLRD is a common disease in every vine- growing region in the world, we believed a survey of Pennsylvania wine grape vineyards was an important and necessary step toward determining the impact of GLRaVs and their associated disease. Only then will we be able to address the effects of these viruses on grape- vine productivity and fruit quality, develop measures to reduce their spread and impact, and provide management information that will contribute to the growth and improvement of the wine grape industry in Pennsylvania. Sampling Over the years, different research teams have devised their own sampling methods in vine- yard blocks of their respective states. The types of tissues to collect and timing of the sample are based on the biology of the virus in the plant. Since these viruses are limited to the phloem tissue in grapevines, tissue samples have involved the collection of woody cane sections (for scrapings of the cambium) during the dormant period, or leaf petioles during the growing season. The concentration of plant viruses typi- cally changes over the course of a year, and GLRaVs are no exception. 4, 13, 14, 17 The most recent evidence seems to show that these viruses are generally most easily detected in petiole or dormant cane samples collected between August and February in California, when the concentration of the virus (titer) was highest in grape phloem tissues. It would also appear that distribution of the virus in different phloem tissues varies among GLRa- V viruses. 13 Pennsylvania survey for GLRaV-1 and 3 Is this disease a problem in Pennsylvania vine- yards, and if so, what can be done about it? Researchers at Penn State University are in the process of answering those questions, and the first step was taken in August 2017. The Penn State grape team delivered a question- naire to the listserv of wine grape growers, asking them if they have observed symptoms of the disease in their vineyards, and if they would like to participate in a statewide, con- fidential survey that would include an assess- ment of their vineyard blocks for the presence of grapevine leafroll-associated viruses. The project then would follow up with tissue sam- pling from participating symptomatic and non-symptomatic vineyards throughout the state, and serological analysis (ELISA) to de- termine the presence of GLRaV -1 and -3, the most common of the leafroll viruses in com- mercial vineyards in Pennsylvania. The col- lection of vineyard samples across the state will continue over two or more seasons and will provide a map of the geographical distri- bution of these viruses on vinifera and hybrid varieties. Labrusca samples will not be col- lected, at least initially. While vineyards were selected from all parts of Pennsylvania, the number of locations favors northwestern and southeastern Penn- sylvania, where the majority of vineyards are located. So far, leaf petiole samples collected from vineyards in Berks, Erie, Snyder and Wyoming counties have been analyzed with serological methods for GLRaV-1 and 3. Sam- ples from Bedford, Chester, Cumberland, Delaware, Lancaster, Lehigh, Northampton, Schuylkill and York counties will be collected in 2018. The results will be made available to growers at various meetings throughout the next several years. Results in 2017 Penn State researchers collected samples of four commonly grown vinifera varieties—Cab- ernet Franc, Pinot Noir, Chardonnay and Ries- ling—and one hybrid variety, Chambourcin, in 34 vineyard blocks in 2017. Of those that have been analyzed thus far, 53% of the vi- nifera vineyard blocks tested positive, with at least one vine with one of the viruses in a block, while 25% of the Chambourcin blocks tested positive. Leaves with symptoms of grapevine leafroll virus with ripe grapes.