Winter Temperature Index for Predicting Stewart’s Wilt in Delaware Sweet Corn, 1999 – 2009

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

Prediction for 2009
Georgetown: 112.0 = Severe – Average monthly temp (Dec, Jan, Feb) = 37.3 °F
Newark: 100.9 = Intermediate to Severe – Average monthly temp = 33.6 °F

For processing and fresh market growers this means that if you are planting sweet corn hybrids that are susceptible or moderately susceptible to Stewart’s wilt, 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. See the 2009 Delaware Commercial Vegetable Production Recommendations for control suggestions.

Average monthly temperatures in °F at Georgetown, DE REC 1999-2009

  2008-2009 2007-2008 2006-2007 2005-2006 2004-2005 2003-2004 2002-2003 2001-2002 2000-2001 1999-2000
December 41.8 39.7 43.5 36.2 38.9 38.6 36.7 43.2 31.2 40.3
January 31.0 36.8 39.7 43.0 34.9 29.5 28.9 40.0 33.8 33.9
February 39.2 39.9 30.1 37.4 36.7 35.2 33.8 39.9 38.8 39.7
INDEX 112.0 116.4 113.3 116.6 110.5 103.3 99.4 123.1 103.8 113.9

Average monthly temperatures in °F at Newark, DE Experiment Station 1999-2009

  2008-2009 2007-2008 2006-2007 2005-2006 2004-2005 2003-2004 2002-2003 2001-2002 2000-2001 1999-2000
December 37.1 37.5 42.5 34.0 35.5 34.0 33.5 43.3 31.1 39.1
January 28.0 35.5 37.3 39.5 31.0 26.4 27.1 39.6 31.5 32.6
February 35.8 36.5 27.8 34.5 34.2 33.1 29.5 40.1 38.4 37.8
INDEX 100.9 109.5 107.6 108.0 100.7 93.5 90.1 123.0 101.0 109.5

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/