UCONN IPM Cucurbits: Bacterial Wilt

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 2 weeks if they are infected 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 on 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 water-soaked 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, stretch 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. Resistance is available in cucumbers for this disease.

By Pamela S. Mercure, IPM Program Assistant, University of Connecticut

References:

Latin, R.X. Bacterial Wilt. p. 36 in Compendium of Cucurbit Diseases, T. A. Zitter, D. L. Hopkins, and C. E. Thomas, eds. APS Press, St. Paul, MN. 1996.

Sherf, A.F. and A. A. MacNab. Vegetable Disease and Their Control. John Wiley and Sons, New York. 1986.

Wick, R. L. 1997. Proceeding of the New England Vegetable and Berry Conference. Cooperative Extension System.

York, A. Pests of Cucurbit Crops. Chapter 5 in Vegetable Crop Pests, R.G. McKinlay, ed. CRC Press, Inc, Boca Raton, FL. 1992

The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law.Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations.The user of this information assumes all risks for personal injury or property damage.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.