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What is the best way to combat powdery mildew in melon plantings? Maximum disease
control requires initiation of a fungicide application program when environmental
conditions favor disease development but before the first visible detection of disease.
Less than optimal but good levels of disease control can also be achieved by beginning
fungicide applications at the very first sign of disease in the field. Early initiation
of fungicide treatment on susceptible melon varieties is essential due to the rapid
development and spread of powdery mildew from the initial and usually undetected
infection sites within the crop. Application of a newly registered novel active
ingredient usually is effective on virtually all of the individual pathogen spores
or colonies developing from spores. However, the very small number of individuals
not killed or inhibited by the fungicide will become an increasingly larger proportion
of the pathogen population as the use of the same active ingredient increases. This
is how resistance to a particular fungicide becomes established. The melon powdery
mildew fungus Podosphaera xanthii has developed significant resistance to some fungicides
in the past. An important strategy to delay development of fungicide resistance
is to alternate among or mix products with different modes of action. Previous research
demonstrated that fungicide application sequences containing a highly efficacious
fungicide alternated with a product of lower efficacy provided a final level of
disease control not significantly different to that achieved by continuous application
of highly effective compounds. Data from these trials support the notion that high
levels of disease control and resistance management can be realized with fungicide
alternation programs containing different modes of action of only highly effective
chemistries as well as application programs incorporating products with high efficacy
along with those that are less effective. Results are available from the 2013 cantaloupe
powdery mildew fungicide evaluation trial conducted at The University of Arizona
Yuma Agricultural Center. These findings should reflect efficacy on melons other
than cantaloupe as well, since powdery mildew on all melons in the desert southwest
is caused by the same pathogen.
To contact Mike Matheron go to: matheron@ag.arizona.edu.
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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
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