Wooster, Ohio
March 19, 2007
Cornfields throughout southern
Ohio might be at risk this growing season for Stewart’s
bacterial wilt and leaf blight -- a corn disease caused by a
bacterium carried and spread by adult flea beetles.
According to the flea beetle index, southern Ohio may be at
moderate to severe risk from Stewart’s wilt. The disease threat
for northern and central Ohio is low to negligible. The model
uses the sum of average temperatures for the months of December,
January and February to assess flea beetle survival and disease
threat levels.
“Despite the assessment, we are advising growers to exercise
caution when relying solely on the flea beetle index due to the
atypical weather conditions we had in December, January and
February,” said Pierce Paul, an
Ohio State University plant pathologist with the Ohio
Agricultural Research and Development Center. “December and
January were very mild and it was very cold in February for a
relatively short period of time. If February’s temperatures had
been normal or mild, our risk levels would have been much
higher.”
Paul, who also holds an Ohio State University Extension
appointment, recommends that growers still scout their fields in
the spring after corn emerges, especially if they’ve planted
hybrids susceptible to Stewart’s wilt.
“Beetles survive in the soil and emerge when soil temperatures
warm to about 65 degrees (Fahrenheit). The flea beetle is a
small, black, shiny insect. Once you know it, you can’t miss
it,” said Paul. “Do a count of the number of flea beetles per
plant. Contact OSU Extension if you have questions or need
treatment recommendations.”
For those growers wanting to take preventive action against the
flea beetle, commercially applied insecticide seed treatments
Cruiser and Poncho or the grower-applied products Concur and
Latitude are labeled for flea beetle control.
The risk of Stewart’s wilt depends on the number of beetles
carrying the bacterium that survived the winter. The greater the
problems with Stewart’s wilt the previous year and the more
overwintering beetles may be carrying the disease, the greater
the risk of Stewart’s wilt in the following season’s crop. The
good news, said Paul, is that Ohio faced few Stewart’s wilt
outbreaks last year.
Stewart’s wilt is characterized by two major disease phases. One
phase is seedling blight. Young plants develop pale green to
yellowish streaks on the leaves. These young plants usually wilt
and die and those that survive are stunted and usually produce
no ears.
The other phase is the leaf blight stage. Leaf blight is
recognized as long, pale green streaks on leaves. As the streaks
enlarge, portions turn pale yellow and eventually become brown.
Streaks may run the entire length of the leaf. A few
characteristic lesions may be seen early in the season, but
numerous lesions are usually not detected until after tasseling.
To learn more about Stewart’s wilt, log on to OSU Extension’s
Ohioline at
http://ohioline.osu.edu/ac-fact/0037.html, or OSU Extension
Agronomic Crops Team Web site at
http://agcrops.osu.edu/.
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