Lincoln, Nebraska
July 4, 2007
Original article with several
photos:
http://cropwatch.unl.edu/archives/2007/crop17/wheat_blackchaff.htm
Black chaff caused by the
bacterium Xanthomonas campestris pathovar (pv.) transluscens has
been confirmed in several wheat fields in Keith County. Disease
incidence (percentage of heads showing black chaff) is higher in
irrigated fields than in rain-fed fields.
Yield losses of up to 40% due to
black chaff have been reported.
 Symptoms
of black chaff include necrotic streaks and blotches on leaves
and darkened glumes (photo). Usually, darkening occurs on the
upper portions of glumes, but entire heads can be darkened.
During wet weather, slime or viscous droplets representing
abundant bacterial growth may appear on diseased tissues. These
exudates appear light-colored and scale-like when dry.
Black chaff is favored by wet weather. It is more common in
irrigated than in rain-fed fields; however, if there is
excessive rain during the growing season, the disease can also
occur in rain-fed fields.
The black chaff bacterium survives on seed. It also can
overwinter on winter cereals and on stubble of small grain
cereals and some wild grasses. Infection of wheat occurs mainly
through stomata and wounds.
Research has shown that under controlled conditions,
transmission of the bacterium from infested seed to seedlings
was higher in a susceptible wheat cultivar than in a resistant
one. However, under field conditions, transmission from infested
seed to seedlings was found to be very low even in the
susceptible cultivar.
The bacterium is spread by splashing water, wind-blown stubble
and water droplets, and plant-to-plant contact.
Recommendations
Black chaff can be managed by planting certified, pathogen-free
seed. Farmer-saved or bin-run seed from fields with black chaff
should not be planted.
Seed raised in fields without black chaff is safe to plant
regardless of the location of those fields. Seed can be
purchased from certified seed producers in southwestern Nebraska
and elsewhere in the state.
Consider hauling all grain from fields with black chaff straight
to the elevator rather than storing it in bins.
Original article with several
photos:
http://cropwatch.unl.edu/archives/2007/crop17/wheat_blackchaff.htm
Stephen Wegulo
Extension Plant Pathologist
Robert Klein
Extension Cropping Systems Specialist |
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