Winter Temperature Index for Predicting Stewart’s Wilt in Delaware Sweet Corn 2000-2010

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

Prediction for 2010
Georgetown: 101.7 = Severe – Avg. monthly temp (Dec, Jan, Feb) = 33.9 °F
Newark: 97.5 = Intermediate – Avg. monthly temp = 32.5 °F

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 2010 Delaware Commercial Vegetable Production Recommendations for control suggestions.

Average monthly temperatures in °F at Georgetown, DE. REC. 2000-2010

2009-2010 2008-2009 2007-2008 2006-2007 2005-2006 2004-2005 2003-2004 2002-2003 2001-2002 2000-2001
December 37.9 41.8 39.7 43.5 36.2 38.9 38.6 36.7 43.2 31.2
January 32.7 31.0 36.8 39.7 43.0 34.9 29.5 28.9 40.0 33.8
February 31.1 39.2 39.9 30.1 37.4 36.7 35.2 33.8 39.9 38.8
INDEX 101 .7 112.0 116.4 113.3 116.6 110.5 103.3 99.4 123.1 103.8

Average monthly temperatures in °F at Newark, DE Experiment Station. 2000-2010.

2009-2010 2008-2009 2007-2008 2006-2007 2005-2006 2004-2005 2003-2004 2002-2003 2001-2002 2000-2001
December 34.9 37.1 37.5 42.5 34.0 35.5 34.0 33.5 43.3 31.1
January 31.6 28.0 35.5 37.3 39.5 31.0 26.4 27.1 39.6 31.5
February 31.0 35.8 36.5 27.8 34.5 34.2 33.1 29.5 40.1 38.4
INDEX 97. 5 100.9 109.5 107.6 108.0 100.7 93.5 90.1 123.0 101.0

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.

Note: Weather records from University of Delaware Carvel REC, Georgetown, 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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