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January 12, 2004
By Paul Vincelli
Kentucky Pest News Number 1008
Last April, Dr. Norm Taylor,
University of Kentucky clover
breeder, and I reported on evidence that the red clover fungus,
Erysiphe polygoni, appears to have become more aggressive in
recent years. Powdery mildew is the most serious disease of red
clover in the U.S., giving leaves a whitish, powdery appearance.
As the disease continues to develop, leaflets turn yellow and
then brown, and they finally die. The disease has not been shown
to reduce yield but can reduce forage quality.
Our evidence that Erysiphe polygoni has become
more aggressive was based on tests conducted by Dr. Taylor at
the University of Kentucky. These tests showed surprisingly high
levels of disease on varieties known for very good to excellent
resistance to powdery mildew, such as Kenland and Marathon (a
Wisconsin variety). Similar tests were recently completed at the
University of Wisconsin, the only other university with a red
clover breeding program. The results of that test, shared with
me by Dr. Taylor, confirm the results of the UK test: that there
appears to be increased aggressiveness of Erysiphe polygoni
across the Midwest.
The most important management option available
for this disease is to select resistant varieties. Given the
current high level of aggressiveness of the fungus, all
varieties can be expected to develop some powdery mildew, but it
would be wise to select varieties with partial resistance such
as 'Freedom!' than a fully susceptible variety, such as a common
red clover. Breeding is underway to increase the resistance of
'Freedom!'. Timely cutting may also help slightly to reduce
quality losses by capturing forage before the disease has fully
developed. |
