Bacterial Wilt

Bacterial wilt is a serious disease caused by Erwinia tracheiphila. It can severely affect cantaloupe, muskmelon, and cucumbers, and, less severely, summer squash and pumpkin. Watermelon is resistant to this disease. Many wild cucurbit species can be infected by this bacterium as well. This disease was first reported in 1893 in Washington D.C. It is now widespread in North America, and is also in Europe and Asia. It is a serious threat to commercial melon production in some areas. It can kill the plants within two weeks if they are infected while young. Spots on fruit predisposes them to storage rots caused by other bacteria.

Symptoms: Symptoms can begin at any time in the season; whenever the beetles that spread the disease are feeding. It is usually more severe early in the season, when the plants are growing rapidly. The first symptom is seen around the chewed areas bacterial willt cucumberon the leaf, where the leaf tissue becomes dull green and the leaf wilts rapidly. The wilt then proceeds outwards in the plant, so that the tip of that vine is wilted. Later, the entire vine will wilt, and finally the entire plant. The leaf may wilt in 5-6 days, and the whole plant in as little as 2 weeks in young plants; older plants generally take longer. Small watersoaked areas appear on the fruit surface. If a spot is cut, small glistening droplets ooze out. Fruit often gets a slime rot in storage from other bacteria invading it at these spots.

Identification of disease: When the stem is cut, a sticky, milky goo oozes out. If the cut ends of the stem are touched together, and then pulled apart, strings of delicate threads, like spider webs, bacterial strands cucumberstretch between the ends. This works well for cucumbers, but not muskmelons. Another way to identify this disease is to put the cut end of the stem in a glass of water. In 15 minutes, one can see bacteria streaming out.

Vector: This disease is spread from infected to healthy plants only by the spotted (Diabrotica undecimpunctata howardi) and striped (Acalymma vittata) cucumber beetles. The striped cucumber beetle has a black head, a yellow-orange thorax, and yellow and black stripes running the length of its body. It is about 1/4" long. The spotted cucumber beetle is about 3/8" long, has a black head, and a yellow to yellowish green body with 12 black spots.

Prevention: The bacteria survive the winter only in cucumber beetles. It is important to control the beetles, especially early in the season. See current recommendations for cucumber beetle control. It may be helpful to remove diseased plants. This must be done regularly, and in all nearby plantings. Resistant varieties of cucumbers are available for this disease.

By Pamela S. Mercure, IPM Program Assistant, University of Connecticut
Photos by Edmond Marrotte, University of Connecticut
References:
Latin, R.X. 1996. Bacterial Wilt in Compendium of Cucurbit Diseases. T. A. Zitter, D. L. Hopkins, and C. E. Thomas, eds. APS Press, St. Paul, MN. p. 36
Sherf, A.F. and A. A. MacNab. 1986. Vegetable Diseases and Their Control. John Wiley and Sons, New York.
Wick, R. L. 1997. Proceedings of the New England Vegetable and Berry Conference. Cooperative Extension System.
York, A. 1992. Pests of Cucurbit Crops in Vegetable Crop Pests, R.G. McKinlay, ed. CRC Press, Inc, Boca Raton, FL. Chapter 5

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