Pumpkin Foliar Disease and Fruit Rot Management Considerations – 2017

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Pumpkins are attacked by many diseases, which makes designing a spray program very difficult. Below are some guiding ideas for management of pumpkins.

There are three areas that growers should address; 1) a general ‘backbone’ program, 2) diseases such as downy mildew and Phytophthora crown and fruit rot, which are not always present, and 3) fruit rots.

A backbone program should begin at the time that the vines begin to run or at the first sign of disease. This program targets many diseases such as anthracnose, white fleck Plectosporium (white speck), black rot, angular leaf spot and bacterial leaf spot. Below is a possible backbone program that can be modified to fit your situation:

Downy mildew and Phytophthora crown and fruit rot are also challenges and the timing management sprays differ. Downy mildew should be sprayed for preventatively, but does not always occur in our area. To avoid unnecessary sprays, scout fields, keep informed of downy mildew sightings in your area and follow the ipmPIPE for cucurbits (http://cdm.ipmpipe.org/).

There are many foliar fungicides that are available for downy mildew on pumpkin. They include Orondis, Ranman, Presidio, Revus, and others (see http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/). This publication also has information on Phytophthora blight, which is managed with alternated sprays of Revus or Ranman and Presidio, Forum or Tanos. If you are planting into a field that has had Phytophthora in the past, a mefenoxam application (Ridomil Gold or Ultra Flourish) should have been applied pre-plant. In addition, foliar applications of Revus or Ranman in alternation with Presidio, Forum or Tanos may reduce disease.

Managing Fruit Rot
Because many different fungi cause fruit rots, no single strategy will be sufficient to manage them. However the following are good practices that, when used together, can minimize damage.

• Select well-drained fields for pumpkin production.
• Select cultivars (varieties) that are less susceptible to fruit rot. For example, there are some cultivar differences in susceptibility to white speck.
• Grow pumpkins on a no-till cover crop. No-till pumpkin production reduces several fruit rots and the reduction in rot is related to the amount of soil coverage that the cover crop provides. A hairy-vetch and rye mixture would provide nutrient benefits and improve fruit quality by reducing rot and edema.
• Follow a good fungicide management program in the field. The same fungi that cause white speck, black rot and anthracnose also cause lesions on the leaves. If the leaves are protected from disease, the fruit will be less likely to become diseased.
• A good fungicide program also will maintain foliage health and keep sunscald at a minimum.
• Bacterial spot on fruit can be controlled with copper fungicide applications that begin when fruit are softball size and continue through fruit set.
• Harvest mature fruit as soon as possible.
• Discard damaged and diseased fruit.
• Avoid wounding the fruit during harvest and transport.
• Store fruit in a cool, shaded and dry location.

One question that I often get is “What about washing fruit?” Because many fungi infect fruit in the field (preharvest) or are seed borne (Fusarium fruit rot), a good field fungicide program will be more effective than washing fruit in reducing fruit rot. However if you do wash fruit, remember that untreated wash water is an excellent way to spread the pathogen from fruit to fruit. A solution of 150 ppm sodium hypochlorite, which is approximately 1/3 oz. household bleach per gallon water will minimize fruit to fruit spread. Fruit should be dried following the wash and stored properly.