Winter Temperature Index for Predicting Stewart’s Wilt in Delaware Sweet Corn 2001-2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Severity Index: < 90, usually absent; 90-100, intermediate; >100, usually severe.

The index is used to predict overwintering flea beetle populations that vector the Stewart’s wilt bacterium, Pantoea stewartii.

Prediction for 2011

Georgetown: 101.9 = Severe         Avg. monthly temp (Dec, Jan, Feb) = 34.0°F

Dover: 97.5 = Intermediate  Avg. monthly temp = 32.5°F

Newark: 94.7 = Intermediate  Avg. monthly temp = 31.6°F

Average monthly temperatures in oF at Georgetown, DE. REC. 2001-2011

2010-11 2009-10 2008- 09 2007-08 2006-07 2005-06 2004-05 2003- 04 2002-03 2001-02
December 31.3 37.9 41.8 39.7 43.5 36.2 38.9 38.6 36.7 43.2
January 31.0 32.7 31.0 36.8 39.7 43.0 34.9 29.5 28.9 40.0
February 39.6 31.1 39.2 39.9 30.1 37.4 36.7 35.2 33.8 39.9
INDEX 101.9 101 .7 112.0 116.4 113.3 116.6 110.5 103.3 99.4 123.1

Average monthly temperatures in oF at Newark, DE Experiment Station 2001-2011

2010-11 2009-10 2008- 09 2007-08 2006-07 2005-06 2004-05 2003- 04 2002-03 2001-02
December 30.8 34.9 37.1 37.5 42.5 34.0 35.5 34.0 33.5 43.3
January 28.7 31.6 28.0 35.5 37.3 39.5 31.0 26.4 27.1 39.6
February 35.2 31.0 35.8 36.5 27.8 34.5 34.2 33.1 29.5 40.1
INDEX 94.7 97. 5 100.9 109.5 107.6 108.0 100.7 93.5 90.1 123.0

Control Strategies

For processing and fresh market growers this means that if you are planting susceptible or moderately susceptible hybrids that flea beetle control is very important. A number of strategies are available including seed treatments, granular insecticides at planting and/or foliar applied insecticides after emergence. For foliar applied insecticides treat susceptible cultivars at spike stage when 5% of the plants are infested. See the 2011 Delaware Commercial Vegetable Production Recommendations for control suggestions.

Note: Weather records from University of Delaware Carvel REC, Georgetown, DE, DE State Fire School, Dover, DE and University of Delaware Ag Experiment Station Farm, Newark, DE. Data records found online at http://www.deos.udel.edu/.

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