Manhattan, Kansas
July 18, 2008
A potentially yield-robbing
disease, gray leaf spot, has surfaced in east Kansas corn
fields, heightening the need for producers to scout their
acreage, a Kansas State University
plant pathologist said.
"Over the past 10 days, levels of gray leaf spot have exploded
in many fields in the eastern half of the state," said Doug
Jardine, plant pathology state leader with K-State Research and
Extension.
"Much of the corn in the west is just starting to reach the
maturity stage when gray leaf spot needs to be monitored."
Gray leaf spot is caused by the fungus Cercospora zeae-maydis.
Jardine said he scouted numerous corn fields in the western half
of the Kansas River Valley (Manhattan to Rossville) the first
week in July. Growth stages there ranged from tassels just
emerging to pollen shed.
"In nearly every field, gray leaf spot lesions could be found
within one to three leaves of the ear leaf. In a couple of
fields, lesions were already present above the ear leaf,"
Jardine said. "It is my understanding that fungicide
applications have begun. Still, every field should be checked
for gray leaf spot progress and development."
Jardine surveyed southeast Kansas July 17-18 and found the corn
there looks healthy, with little evidence of gray leaf spot.
"Most of the corn in southeast Kansas is mature enough that gray
leaf spot is likely not to be a problem for the remainder of the
season,"
he said.
If the forecast for continued humid weather and scattered
thundershowers materializes in the rest of eastern Kansas
however, the disease will continue to develop, he said. For
fields where the disease is already above the ear leaf,
producers should consider using a triazole or
triazole-containing fungicide, such as Quilt ® , Stratego ® ,
Tilt ® , Bumper ® , or Propimax ®. In fields where the disease
has made less progress, strobiluron fungicides such as Headline
® or Quadris ® can work well.
"The most severe disease outbreaks will occur where susceptible
hybrids are being grown in a corn-after-corn or no-till
situation,"
the plant pathologist said.
Producers can estimate returns that may come from applying a
fungicide to a field with heavy gray leaf spot, Jardine said.
With the following formula, for example, a grower might use
these
assumptions: Yield potential of 110 bushels per acre; fungicide
application at a cost of $22 per acre; gray leaf spot at or
above the ear leaf; and a selling price of $7 per bushel:
5 percent loss to disease =
~ $16 net return
10 percent loss to disease = ~ $53 net return
15 percent loss to disease = ~ $90 net return
20 percent loss to disease = ~ $129 net return
Higher yields would result in
higher net returns, Jardine added.
Mention of a trade name in this article does not necessarily
imply endorsement by Kansas State University.
K-State Research and Extension is a short name for the Kansas
State University Agricultural Experiment Station and
Cooperative Extension Service, a program designed to generate
and distribute useful knowledge for the well being of Kansans.
Supported by county, state, federal and private funds, the
program has county Extension offices, experiment fields, area
Extension offices and regional research centers statewide. Its
headquarters is on the K-State campus in Manhattan. |
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