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

Station

NO. 12

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 Re-search Station has only accu-mulated 1755 growing de-gree days (GDD) (base 50; modified). In comparison, the extremely warm growing sea-son of 2012 resulted in the accumulation of 2300 GDD on September 14, 2012. 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 maturi-ty. 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 accu-

mulate 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 15.4. 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 accu-

mulate until October 10.

Figure 1. Growing degree days (base50) accumulated from April 1 to September 14 for the years 2011-2014 at the Peninsular Agricultural Research Station, Stur-geon Bay, WI.

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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, 2012. Where-as in 2013, only 2,132 GDD accumulated by October 10. Of course brix is only one quality parameter, what hap-pens to the TA over time? The data for TA was com-bined for the years stated above and linear regression was used to establish a line (Figure 3). The line is de-scribed as, Y=42.62-0.0119x. 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 fac-tors substantiates research from the University of Minne-sota. 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, loca-

tion, canopy management,

pest pressure, and crop

load. In the data used

above, the crop loads were,

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.

Figure 2. Brix levels in Marquette juice at various growing degree days (GDD). Line is described by the equation; Y=0.019x - 21.8. Data points from 2011-2013 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 de-scribed by the equation; Y=42.62 - 0.0119x. Data points from 2011-2013 from cultivar trial at the Penin-sular Agricultural Research Station, Sturgeon Bay,

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References Hagerty, L. 2012. Understanding the ripening chemistry of cold-hardy wine grapes to predict optimal harvest times. Northern Grapes News. Vol. 1, Issue 3. http://northerngrapesproject.org/wp-content/uploads/2012/08/2012-Aug-15-Newsletter.pdf

Dami, I. and P. Sabbatini. 2011. Crop estimation of grapes. The Ohio State University Extension. http://ohioline.osu.edu/hyg-fact/1000/pdf/1434.pdf

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 moni-toring

• 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

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Development of wine grapes in the grape variety trials at the Peninsular Agricul-tural Research Station (PARS) Sturgeon Bay, WI and West Madison Agricultural Research Station (WMARS), Madison, WI

2014

Brianna at WMARS

Foch at WMARS

Brianna at PARS 9.15.2014

Foch at PARS 9.15.2014

Frontenac at PARS 9.15.2014

Frontenac at WMARS 9.16.2014

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Development of wine grapes in the grape variety trials at the Peninsular Agricul-tural Research Station (PARS) Sturgeon Bay, WI and West Madison Agricultural Research Station (WMARS), Madison, WI

2014

La Crescent. At WMARS

La Crosse at WMARS

Marquette at WMARS

La Crescent at PARS 9.15.2014

La Crosse at PARS 9.15.2014

Marquette at PARS 9.15.2014

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Degree Day1 (base 50) Accumulation from April 1 to September 14, 2014

at Peninsular Agricultural Research Station in Sturgeon Bay, WI

Date 2014 2013 5 Year Average2

4/1 to 9/14 1,755 1,904 2,104

1Modified method. 2Average from 2009 to 2013.

Degree Day1 (base 50) Accumulation from April 1 to September 14, 2014

at West Madison

Date 2014 2013 5 Year Average2

4/1 to 9/14 2,371 2,471 2,577

1Modified method. 2Average from 2009 to 2013.

Accumulated degree days1 (base 50) for the month of March in Sturgeon Bay and

Madison, WI.

1Modified method. 2Data from http://www.doa.state.wi.us/degreedays/

Year Madison WI Sturgeon Bay WI

2013 1 0

2012 252 106

2011 13 3

2010 72 38

2009 51 12

2008 1 0

2007 90 41

2006 22 7

2005 40 9

2004 49 11

GDD (base 50, ceiling 86)

2014 22 2

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)746-

2260 or dean.volenberg@ces.uwex.edu