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 nove l 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 develops within the pathogen population.
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. In the two
most recent (2014, 2015) fungicide evaluation trials conducted at the University
of Arizona Yuma Agricultural Center, tested fungicides that reduced the leaf area
covered with powdery mildew on Olympic Gold cantaloupe plants by at least 90%, compared
to nontreated plants, included Luna Sensation (fluopyram+trifloxystrobin), Mettle
(tetraconazole), Procure (triflumizole), Quintec (quinoxyfen), Rally (myclobutanil),
Rhyme (flutriafol), Torino (cyflufenamid), and Vivando (metrafenone). 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. Some of these
tested fungicides may not currently be registered for use on melons, so read labels
carefully before considering their use.
