ANR-1067 PLANT DISEASE NOTES: WHEAT SCAB OR HEAD BLIGHT
ANR-1067, New Aug 1997. William
S. Gazaway, Extension Plant Pathologist,
Professor, Plant Pathology, Auburn University
Plant Disease Notes
Wheat Scab Or Head Blight
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Wheat scab or head blight is one of the more damaging
diseases of wheat in the United States. Nationwide, this disease
has caused the wheat industry millions of dollars in yield losses.
In the Midwest and High Plains, scab is the major obstacle to
wheat production in recent years. Fortunately, scab has not been
a major problem for wheat growers in Alabama. Scab can be an occasional
problem in the more humid wheat growing areas of the Gulf Coast.
Scab in addition to attacking wheat also attacks and reproduces
on barley, oats, and corn.
Head blight or wheat scab is caused by several Fusarium species.
These fungi survive on plant debris. They invade and damage the
spikelets of the grain head during flowering, thus preventing
or partially impeding the development of grain in the grain head.
The invading scab fungi can either kill part of the grain head
or the entire grain head. Some infected seeds, that are not killed
by the scab fungus, are low in vigor and often fail to germinate.
Infected seed that germinate often die early in the seedling stage
due to Fusarium crown rot or root rot, causing poor stands in
the following crop. In addition to poor, unthrifty stand, yield
losses can be quite high if conditions are favorable for development
of the disease.
Scab infected grain also produces a toxin that is reported
to be harmful to nonruminant animals.
Barley infected with scab cannot be used for making beer because
it causes excessive foaming.
Symptoms. In the field, wheat with bleached or partially
bleached spikes is the most easily recognized symptom of scab.
Symptoms usually first appear during or shortly after flowering.
A few or all of the spikelets on the spike may be bleached. If
the rachis is infected, the spike above the point of infection
will bleach out. Frequently, the entire head is bleached and devoid
of grain. During wet, humid conditions, a light pink or white
growth (fungal mats) may be seen on the glumes of infected grain.
Later, tiny fruiting bodies resembling pepper grains will appear
on the surface of the grain. Infected grain is underweight and
shriveled. Infected seed either fail to germinate or produce weakened
seedlings that usually die soon after they emerge from the soil.
Persistence And Spread. Fusarium species that cause
wheat scab or head blight survive and reproduce on volunteer wheat,
grass hosts, or on plant debris and other organic matter in the
soil. These species are present in most fields and can spread
to and infect wheat when favorable environmental conditions (warm,
moist weather) exist. Spores are blown from Fusaria living on
plant debris in the soil and other weed host plants to wheat spikelets.
Under warm, moist conditions spores land on spikelets, germinate,
and invade glumes, floral parts, and other susceptible plant parts.
Most scab infection occurs during flowering or shortly after the
flowering period.
Control. Wheat scab or head blight is best controlled
by using the following strategies:
- Fungicide seed treatment is somewhat effective. It can reduce
carry over of scab fungi on the seed's surface, but it will not
stop carry over of scab within the seed.
- A 1-year rotation with a nonsusceptible host between wheat
crops will reduce scab inoculum in the field. Do not rotate corn
or grain sorghum with wheat since they are also hosts to scab.
- Avoid minimum tillage where scab is a problem. Plant debris
left on the surface of the soil serves as an excellent substrate
for Fusarium to reproduce and increase its inoculum.
- After harvest, plow under and bury wheat stubble and other
debris left on the soil's surface.
- Timely foliar applications of fungicides have been ineffective.
Although propicanozole (Tilt) and benomyl have partially controlled
scab, it is questionable whether they are cost effective.
Use chemicals only according
to the directions on the label. Follow all directions, precautions,
and restrictions that are listed.
The pesticide rates in this
publication are recommended only if they are registered with the
Environmental Protection Agency and the Alabama Department of
Agriculture and Industries. If a registration is changed or canceled,
the rate listed here is no longer recommended. Before you apply
any pesticide, check with your county Extension agent for the
latest information.
Trade names are used only to
give specific information. The Alabama Cooperative Extension System
does not endorse or guarantee any product and does not recommend
one product instead of another that might be similar.
For more information, contact your county Extension
office. Look in your telephone directory under your county's name
to find the number.
For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information.
Issued in furtherance of Cooperative Extension work in agriculture and
home economics, Acts of May 8 and June 30, 1914, and other related
acts, in cooperation with the U.S. Department of Agriculture. The Alabama
Cooperative Extension System (Alabama A&M University and Auburn
University) offers educational programs, materials, and equal
opportunity employment to all people without regard to race, color,
national origin, religion, sex, age, veteran status, or disability.
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