Volume 1 Issue
2 May
28, 2004
Wheat Disease Summary:
Around the U.S. in a Few Short Paragraphs
Fusarium head blight (FHB)
While FHB spores don’t travel on winds from southern
states to “rain” on Minnesota fields like rusts, it may be
of interest to note what the FHB disease pressure is in
other U.S. wheat growing areas.
- Arkansas:
Gene Milus at the University of Arkansas reports
widespread FHB symptoms throughout fields. He
estimates that this year may rival 1991 when
substantial levels of scab were reported throughout
the state.
- Indiana:
As of May 24, Greg Shaner at Purdue University
reported that wheat was in the watery ripe stage.
Unfortunately, scab was favored during flowering due
to several days of wet weather. It’s still too early
to tell how much impact FHB will have in that state.
- Kentucky:
Don Hershman at the University of Kentucky reports
that a few fields in the southern part of the state
have nearly uniform scab symptoms (e.g., symptoms on
at least one floret per head), but he doesn’t expect
the rest of the state to be so diseased. Disease
severity (e.g., the number of spikelets per head with
symptoms) in areas hit hard with FHB is about 40%.
- Missouri:
Laura Sweets at the University of Missouri reports
winter wheat varieties are just past the flowering
stage in Columbia. FHB is just beginning to show up in
the southern part of the state. Again, disease impacts
in Missouri are as yet unknown.
Rusts
Wheat leaf rust. According to the Cereal Rust
Bulletin published the USDA-ARS Cereal Disease Lab in St.
Paul (http://www.cdl.umn.edu/index.htm),
wheat leaf rust has been more severe this year in the
southern U.S., compared with last year. Disease severity
was reported as moderate to severe on susceptible
varieties in Texas up until harvest. The disease is now
becoming established across Oklahoma, Kansas, Arkansas,
and Missouri. However, dry conditions in some locations
have slowed its advance.
Winds blowing from the south into Minnesota are known
to deposit leaf rust spores in the state. If the weather
favors disease development (e.g., 6 to 8 hours leaf
moisture and temperatures between 60o to 80oF), there are
plenty of rust spores in southern states to support
getting the disease established here. This will be
something to watch as the growing season advances.
 Wheat
stripe rust (Figure 1). Stripe rust appears to be less
severe this year across southern states compared with
2003. Some disease hotspots exist (e.g., northern
Arkansas, central and southwestern Oklahoma), but overall,
populations of stripe rust spores were not produced this
year like they were in 2003.
Stripe rust requires slightly cooler temperatures than
leaf rust and it’s generally not favored by Minnesota’s
hot summer weather and warm nights. Last year, it was
unseasonably cool during early summer which effectively
opened the door to this disease. This spring has also been
unseasonably cool. If we don’t get warmer temperatures in
June, we may see stripe rust once again if spores blow in
from southern states.
Barley Yellow Dwarf
In early May, Bob Hunger at
Oklahoma State University observed widespread barley
yellow dwarf symptoms, but diseased plants didn’t appear
to be significantly stunted. However, the disease is more
severe this year in northern Arkansas than in past years,
according to Gene Milus.
Aphids infected with the barley yellow dwarf virus can
‘ride’ on the winds from southern states to be deposited
in Minnesota fields during the growing season. The earlier
insects infect susceptible plants, the more severe plant
symptoms will be and the greater the risk for yield loss.
Crop disease survey summaries are regularly updated
during the growing season at:
http://www.mda.state.mn.us/pestsurvey/PestReports/PestReport.html
by the Minnesota Dept. of Agriculture. Another tool
available is the online FHB (scab) Prediction model:
http://mawg.cropdisease.com.
Char Hollingsworth Small Grains
Extension Plant Pathologist
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