Bacterial wilt

Bacterial wilt is a cucurbit disease caused by the pathogen Erwinia tracheiphila, a Gram-negative bacterium in the family Enterobacteriaceae. Cucumber and muskmelon plants are most susceptible, but squash, pumpkins, and gourds may also become infected. Watermelons are immune to the disease.

Disease Transmission
E. tracheiphila is spread between plants by insect vectors. Striped cucumber beetles (Acalymma Vittatum) and spotted cucumber beetles (Diabrotica undecimpunctata) acquire the bacteria by feeding on infected plants, then carry the bacteria in their digestive tracts. The disease may be spread to susceptible plants through feeding wounds.

Symptoms & Diagnosis
Bacterial wilt is a disease of the vascular tissue. When a plant is infected, E. tracheiphila multiplies within the xylem, eventually blocking water transport. The first sign of infection may be wilting of individual leaves on a single stem. However, the disease will eventually spread down the runner and then infect the whole plant, causing it to shrivel, turn brown, and die. There is a diagnostic test for bacterial wilt that can be done in the field. The presence of the bacteria causes the sap to become a milky color and makes it a sticky consistency. If the stem is cut near the crown and the ends are held together then slowly pulled apart, the sap should form a string between the ends.

Treatment & Prevention
Once a plant is infected, there is no way of stopping the spread of the disease. Some cucurbit cultivars are less susceptible than others, so it be beneficial to plant these cultivars. However, the most effective preventative measure is to keep beetle populations as low as possible through careful monitoring and insecticide sprays.

= References =
 * "Bacterial Wilt" by APSnet
 * "Bacterial Wilt Factsheet" by Cornell University Plant Disease Clinic