Anthracnose of cucurbits

How to tell anthracnose apart from other cucurbit issues

• Anthracnose can infect all above-ground plant parts. Symptoms vary depending on which cucurbit it infects.
• Irregular brown leaf spots form on squash, melon and cucumber. The center of the leaf spot may drop out resulting in a ragged appearance. This is most common on cucumbers.
• Cucumber leaf spots often have a yellow halo.
• Watermelon leaf spots are smaller and dark brown to black.
• Sunken elongated stem infections can occur on cucumber and melon but are not common on other cucurbits. Infections on melon often exude a reddish gum.
• Fruit infections are sunken black spots 1/4 -1/2 inch across and 1/4 inch deep. Spots may have fluffy white cotton-like mycelia and sticky salmon-colored spores during wet weather.

Biology

• The fungus Colletotrichum orbiculare causes anthracnose. This pathogen can attack all cucurbits, but the most severe disease is on cucumbers, muskmelons and watermelons.
• The anthracnose fungus can survive in infected plant debris and seed.
• Spores form on infected leaves and fruit. These easily spread by splashing rain, irrigation, on hands and tools.
• The disease develops in warm, moist environmental conditions.
• Anthracnose first appears mid to late season after the canopy closes.
• During wet summers, the disease can be quite severe.

How to manage anthracnose in the home garden

• Some resistant varieties of cucumber are available.
• Purchase clean seed from a reputable source. Do not save seed from infected plants.
• Rotate vegetables so three years go by before planting any member of the squash family in the same location.
• Avoid getting leaves wet with water by using drip irrigation, a soaker hose, or careful watering technique.
• Do not work in plants when wet.
• Remove and destroy infected vines at the end of the season in small gardens.
• After working in an infected area, clean and sanitize any tools you used, and clean dirt off of your shoes.