Cropland disease. Powdery mildew is widespread on winter wheat in the triangle. (19
February, 2016)
Powdery mildew is very widespread on winter wheat in Montana from Great Falls to Havre.
Lesions are sporulating on lower leaves, and may have an orangish cast. These are from fall
infections, and persisted due to our mild fall and winter.
Lesions are defined and powdery, not in stripes. This is NOT stripe rust. Powdery mildew starts
out grey/white, and forms hard black pinprick sized spores called cleistothecia further along in
disease development. Pictures are below. Disease development is optimal between 59° and 72°F
and is significantly reduced above 77°F. Powdery mildew is favored by drought stress, dense
stands, high nitrogen fertility, rapid plant growth, and shady conditions. Spore germination is
inhibited by free water but the pathogen prefers high humidity (75-100%) for infection.
Based on reports from growers last year, results from the use of fungicides at the tillering stage
were erratic. Powdery mildew, if it remains restricted to the lower leaves, should have minimal
effects on yields except if the variety is extremely susceptible (as many Montana varieties are)
and leaf death occurs. There is no guarantee of an economic benefit, but you may consider the
use of a fungicide combined with your herbicide if disease is present. All varieties in Montana are
susceptible to this disease, although there may be some variation in the degree of susceptibility.
Please use full rates for fungicides if you choose to apply one; most products are rated good to
very good (most recent fungicide efficacy table attached to this agalert). A good tool to play with
the economic benefit of a fungicide application can be found at:
https://www.msuextension.org/econtools/fungicide/index.html
Fact sheets: http://ohioline.osu.edu/ac-fact/0010.html and
http://www.ianrpubs.unl.edu/pages/publicationD.jsp?publicationId=1262
https://www.agric.wa.gov.au/spring/managing-powdery-mildew-wheat
(Cropland diseases. Mary Burrows. mburrows@montana.edu; 994-7766)
Symptoms/signs of powdery mildew on winter wheat. Note the greyish cast, scattered lesions,
and powdery appearance.
More symptoms/signs.
A close up of the lesions under the microscope. There is a bit of an orangish cast, but it’s not pure
orange, and the fungus is very ‘powdery.’
Cleistothecia forming as the disease matures in the field and temperatures are warmer
As a comparison, this is fall infection of stripe rust:
And a full blown infection of stripe rust: