How To Control Damaging Diseases In Melons
April 14, 2015 
To manage Fusarium wilt, be sure to carefully manage cultural factors such as crop rotation and water management.
Photo credit: Amanda Gevens
For melon growers, a few of the top diseases to be on the lookout for this season include Fusarium wilt, angular leaf spot, and powdery mildew.
Fusarium Wilt
According to Amanda Gevens, assistant professor and Extension plant pathologist in potatoes and vegetables at the University of Wisconsin, Fusarium wilt has the potential to be the most problematic.
To manage the soil borne fungal disease, Fusarium wilt, growers must carefully manage cultural factors such as crop rotation and water management to limit the buildup of the pathogen in the soil.
“Typically, Fusarium wilt becomes a problem when multiple years of cucurbits are grown in the field without or with limited rotation to other non-hosts,” Gevens says. “A minimum of five years out of a cucurbit host is recommended to limit this disease. Varietal resistance can also be utilized to limit disease. Fungicides, however, are not useful for control of this disease.”
Angular Leaf Spot
For angular leaf spot, which is a foliar and fruit bacterial disease of melon and other cucurbit crops, management includes planting of pathogen-free seed and resistant varieties, when they are available. According to Gevens, to keep disease at bay, do not grow cucurbits in the same field more than once every three or four years and avoid excessive nitrogen fertilization.
In addition, be sure to pay attention to all aspects of water use. “Limit the use of overhead irrigation and avoid cultivating, harvesting, or handling plants when they are wet. It is helpful to plow under or remove crop debris following harvest if the field was severely affected by angular leaf spot to remove pathogen from the field. A bactericide, most commonly a copper containing fungicide, can be applied at first sign of disease.
“Typically, if conditions favor angular leaf spot, other foliar fungal pathogens are also active, and I typically recommend a tank-mixed fungicide application of a copper, plus a fungicide for control of both bacterial and fungal diseases.”
Powdery Mildew
Powdery mildew is a disease that can home in on melons, and sometimes present a severe problem for this crop. Depending upon the environmental conditions, variety, and disease onset, management by chemical means may be necessary.
“Some powdery mildew can be tolerated in cucurbit crops, however, early season infection can result in premature defoliation which leads to yield and quality losses,” Gevens says.
There are several effective fungicides for control of powdery mildew in cucurbit (melon) crops including the conventional fungicides myclobutanil (if resistance has not developed in your area), and quinoxyfen.
Many fungicides with activity are registered but Gevens says she chose these two as in recent field trials in Wisconsin, researchers saw greatest efficacy with quinoxyfen and myclobutanil with some resistance in pockets across the state.
In organic systems, Gevens says coppers, sulfurs, and oils can be used in managing powdery mildew. “In our 2014 field trials, we saw limited efficacy with these materials for powdery mildew control, however disease pressure was very high.
“It is important to understand how and when to apply fungicides for powdery mildew control,” she says. Some products need to be applied before outbreaks are severe, while others can offer some curative activity. Crop rotational strategies typically are ineffective for powdery mildew control in cucurbits because the pathogen/inoculum source is often not within the field, but rather local or at longer distances away from your production field of management.
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