The long awaited harvest of melons and winter squash has arrived in Minnesota. Many gardeners are surprised to find sunken spots, rings, unusual color patterns, or raised corky scabs on the fruit. What caused all of these unusual spots and can the fruit be eaten?

Fruit spots can be caused by a number of different factors including fungal and viral plant pathogens. Melons, cucumbers, winter squash, and summer squash are all in the same plant family, the Cucurbitaceae. As a result, these crops often suffer from the same plant disease problems. Although many of the vine crops share disease problems, how severe the disease problem becomes varies by crop and by variety. Below are a few common disease problems found on melons and squash at harvest in Minnesota.   Several different mosaic viruses can infect squash and melon in Minnesota. Viruses may be spread by insects like aphids or cucumber beetles, on sap on hands and tools, or in infected seed. Infected plants have mosaic patterns of dark and light greens on the leaves and leaves may be puckered or distorted. Fruit produced on virus infected plants often have unusual color patterns, ring spots, and may be malformed. Yes, you can eat squash and melons that are infected with mosaic virus. These viruses are not harmful to humans and do not cause the fruit to rot. Often the discoloration is only skin deep. In cases where fruit are severely distorted, the texture of the fruit may be affected and may not be desirable for eating. There are several different fungi that cause fruit rot in squash and melon. Scab and anthracnose are common in Minnesota. Both of these diseases start as a leaf spot disease and eventually infect fruit. The type of spot that occurs on the fruit depends on which disease is present and how susceptible or resistant the plant is. Anthracnose causes sunken round spots in the fruit of cucumber, squash, and melons. If moisture is present, fluffy fungal growth and powdery salmon colored spores can be seen within the fruit spot. Scab causes sunken round spots on cucumber, summer squash, and pumpkin that may be covered with a dark green to black velvety fungal growth when humidity is high. Some types of winter squash are moderately resistant to scab and will develop a raised corky bump on the fruit instead of a sunken spot. Resistant varieties are available for scab and anthracnose in some crops.  Fungal fruit spot diseases will rot the fruit of the squash or melon. This rot begins just below the sunken spot visible on the outside of the fruit. In cases where only a few fruit spots occur, rotten areas can be cut out and the remainder of the fruit can be cooked and eaten. Carefully inspect winter squash at harvest. Only fruit with no signs of a fruit spot disease should be stored as rot can progress in storage.

Sometimes so many spots are present that the majority of the fruit is rotten. In other cases a fruit spot may crack open and secondary bacteria and fungi or fruit feeding insects will move into the fruit. In both situations, this fruit should be removed from the garden and buried in a compost pile that heats up and breaks down plant material completely.

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Listen to our interview here, on the fruit and vegetable podcast called, "What's Killing My Kale?" Click on "Episode 12" and listen to the audio file.
Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production

 

Tar spot on maple M.Grabowski, UMN Extension

Many birds, native pollinators, and other wildlife utilize the plants in our landscapes to help survive the winter. 

While it is important to remove diseased plant material from the yard and garden to reduce the survival of plant pathogens, it is also important to leave healthy flower stalks, seed heads, grasses, fallen leaves, and other plant parts in the garden to support Minnesota’s pollinators and wildlife. 
M. Grabowski, UMN Extension Educator