Good Fruit Grower

March 15

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Early leaf removal in white grapes has several benefits. by Melissa Hansen I n eastern Washington State, leaf removal in wine grapes is typically done between fruit set and bunch closure to open up the canopy, reduce disease pres- sure, and improve fruit quality. But is that the best time? Washington State University researchers studied fruit zone leaf removal in eastern Washington the last two years, looking at the effects on vine development and fruit quality in white wine grapes. This year, they are expanding the research to red varieties and will study how leaf removal influences wine quality. "Initially, we looked at white varieties and leaf removal from the aspect of disease management," Dr. Michelle Moyer, WSU extension viticulturist, told Good Fruit Grower. "White varieties give us a lot of disease problems because they are the most susceptible to fungal diseases like powdery mildew and Botrytis bunch rot." Moyer and WSU graduate student Brittany Komm wanted to learn if growers could remove leaves earlier than fruit set—before or during bloom—to improve dis- ease management without impacting vine development or yield. They also wanted to learn if earlier leaf removal would reduce sunburn severity by acclimating fruit to high levels of solar radiation earlier in the season. In the past, studies that evaluated fruit zone leaf removal showed significant reductions in fruit set and yield when leaves were removed early, around bloom time, said Moyer. "However, these studies were con- ducted in cooler climates than that of eastern Wash- ington. We wanted to find out if the warmer, more arid climate of eastern Washington would help reduce possible negative side effects on fruit set and yield when leaf removal was done early." Moyer and Komm set up trials in commercial vine- yard blocks of Sauvignon Blanc and Riesling planted in 2007. The blocks, located north of Prosser, have identi- cal pest management programs, are both spur pruned and drip irrigated, and have canopies trained to a modi- fied vertical shoot position trellis. During the growing seasons of 2012 and 2013, WSU tested four leaf removal treatments: control (no leaf removal); prebloom; bloom; and four weeks postbloom. All leaves were removed by hand. Vines were treated the same both years. Leaf removal was defined as removing all basal leaves and lateral shoots from the base up to and opposite of the second cluster on all fruiting shoots. Conclusions Moyer highlighted the following results: Vine development • Fruit-zone leaf removal did not alter the vines' nutrient status. • Timing of leaf removal did not significantly impact fruit set or berry size at harvest. • Exposing buds through leaf removal before and during bloom helped increase bud surface temperatures during this key developmental period. • Leaf removal did not negatively impact cold hardiness, based on preliminary results. Fruit quality • Prebloom and bloom leaf removal significantly improved spray penetration. Bloom period is a crit- ical time for disease management; maximum spray penetration into clusters can help prevent powdery mildew and bunch rot. • No significant differences were observed in fruit quality at harvest (Brix, titratable acidity, and pH) between the different leaf removal timings. 32 MARCH 15, 2014 GOOD FRUIT GROWER Yields not affected by Grapes

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