Vineyard IPM Scouting Report for week of 15 September 2014 UW-Extension Door County and Peninsular Agricultural Research Station

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1 NO Vineyard IPM Scouting Report for week of 15 September 2014 UW-Extension Door County and Peninsular Agricultural Research Station Cold Slows Grape Maturity Grape maturity is reliant on a number of factors, but heat units are a major factor that will result in the grape crop reaching quality standards. The 2014 growing season has been cooler than the last three seasons (Figure 1). As of September 14, 2014 the Peninsular Agricultural Research Station has only accumulated 1755 growing degree days (GDD) (base 50; modified). In comparison, the extremely warm growing season of 2012 resulted in the accumulation of 2300 GDD Figure 1. Growing degree days (base50) accumulated from April 1 to September 14 for the years at the Peninsular Agricultural Research Station, Sturgeon Bay, WI. on September 14, The question many growers are asking, will the crop reach maturity for quality standards. Research out of the University of Minnesota found that 2,500 to 2,725 GDD resulted in most cold-climate wine grapes achieving peak maturity. However, the Door County Peninsula and other northeastern counties near Lake Michigan seldom ever accumulate 2,500 GDD before a killing frost. Which brings me back to the question, can we achieve grape quality in locales with limited accumulation of GDD? Using data from the cultivar trial at PARS for Marquette over the last 3 years (2011, 2012, and 2013) suggest that it will be very difficult to attain desirable brix levels prior to a killing frost this year. The brix of grapes increase as growing degree days accumulate in a very linear trend after the onset veraison (Figure 2). The problem this year is that we have yet to accumulate 1,800 GDD and the data set does not include points under 1,830 GDD. This Monday I performed a quality analysis for a grower near the PARS and the Marquette grapes had a brix reading of If these would have been harvested, the alcohol of the wine would have been approximately 9.2% (v/v). Most growers would be looking to harvest Marquette at 22 to 24 brix that would result in the finished wine having an alcohol content between 12.9 to 14.2% (v/v). According to the equation; y=0.019x 21.8 that describes the line in Figure 2, I calculated how many GDD would be needed to attain a brix reading of 23. According to the equation, 2,357 GDD would be needed to attain a brix reading of 23. In 2011, 2,357 GDD did not accumulate until October 10.

2 2 This is on the threshold of a fall frost event of 32 F as there is a 50% chance that a frost will occur on or before October 10. In contrast, 2,364 GDD accumulated by September 11, Whereas in 2013, only 2,132 GDD accumulated by October 10. Of course brix is only one quality parameter, what happens to the TA over time? The data for TA was combined for the years stated above and linear regression was used to establish a line (Figure 3). The line is described as, Y= x. Plugging in the 2,357 GDD into the equation for x, results in a TA of 14.5 g/l. The TA for Marquette in the cultivar trial of PARS has seldom dropped below 15 g/ L. This quick comparison of two quantifiable quality factors substantiates research from the University of Minnesota. That being brix levels reach harvest levels prior to suitable TA levels. A number of other factors play a role in brix and TA levels. These factors can be impacted by cultivar, location, canopy management, pest pressure, and crop load. In the data used above, the crop loads were, Figure 2. Brix levels in Marquette juice at various growing degree days (GDD). Line is described by the equation; Y=0.019x Data points from from cultivar trial at the Peninsular Agricultural Research Station, Sturgeon Bay, WI. Figure 3. Titratable acidity (g/l) in Marquette juice at various growing degree days (GDD). Line is described by the equation; Y= x. Data points from from cultivar trial at the Peninsular Agricultural Research Station, Sturgeon Bay, 4.32, 3.82, and 7.61 tons/acre for 2011, 2012, and 2013, respectively. By tracking quality parameters over time using GDD provides you the opportunity to estimate harvest dates. In addition, this information will allow the winery operator to adjust wine styles to how the grapes are maturing. This will be more important this year as limited GDD will result in many cultivars not achieving peak harvest parameters.

3 3 References Hagerty, L Understanding the ripening chemistry of cold-hardy wine grapes to predict optimal harvest times. Northern Grapes News. Vol. 1, Issue 3. Dami, I. and P. Sabbatini Crop estimation of grapes. The Ohio State University Extension. Spotted Wing Drosophila (SWD) Update as of September 11, 2014 According to Emma Pelton working with Christelle Guedot on SWD in grapes at UW-Madison This season they have trapped SWD in all 7 vineyards they have been monitoring All six cultivars being monitored with traps have SWD present The SWD population has increased over time from the start of monitoring at pre-veraison Findings Low levels of fruit fly larvae, approximately 1 larva per 1 to 2 medium grape clusters Most vineyards in the study are infected with fruit fly Most cultivars are infected with fruit fly Grapes that are infected with larvae were reared to adults and they have been identified as SWD Grapes appear to not be a preferred host. Emma is currently working on grape cultivar susceptibility to SWD. Thanks Emma

4 4 Development of wine grapes in the grape variety trials at the Peninsular Agricultural Research Station (PARS) Sturgeon Bay, WI and West Madison Agricultural Research Station (WMARS), Madison, WI Brianna at PARS Brianna at WMARS 2014 Foch at PARS Foch at WMARS Frontenac at PARS Frontenac at WMARS

5 5 Development of wine grapes in the grape variety trials at the Peninsular Agricultural Research Station (PARS) Sturgeon Bay, WI and West Madison Agricultural Research Station (WMARS), Madison, WI La Crescent at PARS La Crescent. At WMARS 2014 La Crosse at PARS La Crosse at WMARS Marquette at PARS Marquette at WMARS

6 6 Degree Day 1 (base 50) Accumulation from April 1 to September 14, 2014 at Peninsular Agricultural Research Station in Sturgeon Bay, WI Date Year Average 2 4/1 to 9/14 1,755 1,904 2,104 1 Modified method. 2 Average from 2009 to Degree Day 1 (base 50) Accumulation from April 1 to September 14, 2014 at West Madison Date Year Average 2 4/1 to 9/14 2,371 2,471 2,577 1 Modified method. 2 Average from 2009 to Accumulated degree days 1 (base 50) for the month of March in Sturgeon Bay and Madison, WI. Year Madison WI Sturgeon Bay WI Modified method. 2 Data from GDD (base 50, ceiling 86) Please scout your vineyards on a regularly scheduled basis in an effort to manage problem pests. This report contains information on scouting reports from specific locations and may not reflect pest problems in your vineyard. If you would like more information on IPM in grapes, please contact Dean Volenberg at (920) or dean.volenberg@ces.uwex.edu