Winter Temperature Index for Predicting Stewart’s Wilt in Delaware Sweet Corn, 1998-2008

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

Prediction for 2008
Newark:        109.5 = Severe- average monthly temp (Dec, Jan, Feb) was 36.5°F Georgetown:  116.4 = Severe – average monthly temp (Dec, Jan, Feb) was 38.8°F

For processing and fresh market growers this means that if you are planting susceptible or moderately susceptible hybrids, 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.

Average monthly temperatures in °F at Georgetown, DE REC 1998-2008

  2007-08 2006-07 2005-06 2004-05 2003-04 2002-03 2001-02 2000-01 1999-00 1998-99
December 39.7 43.5 36.2 38.9 38.6 36.7 43.2 31.2 40.3 41.3
January 36.8 39.7 43.0 34.9 29.5 28.9 40.0 33.8 33.9 39.5
February 39.9 30.1 37.4 36.7 35.2 33.8 39.9 38.8 39.7 38.7
INDEX 116.4 113.3 116.6 110.5 103.3 99.4 123.1 103.8 113.9 119.5

Average monthly temperatures in °F at Newark, DE Experiment Station 1998-2008

  2007-08 2006-07 2005-06 2004-05 2003- 04 2002-03 2001-02 2000-01 1999-00 1998-99
December 37.5 42.5 34.0 35.5 34.0 33.5 43.3 31.1 39.1 41.0
January 35.5 37.3 39.5 31.0 26.4 27.1 39.6 31.5 32.6 34.8
February 36.5 27.8 34.5 34.2 33.1 29.5 40.1 38.4 37.8 38.0
INDEX 109.5 107.6 108.0 100.7 93.5 90.1 123.0 101.0 109.5 113.8

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. Thanks for the data go to Dean Dey at Georgetown and Scott Hopkins, Farm Manger, UD Ag Experiment Station, Newark.

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