About Bacterial Wilt
Bacterial Wilt is a disease caused by the bacterium Erwinia tracheiphila, affecting the cucurbits family. The bacteria survive through the winter by overwintering in the digestive system of the cucumber beetle. Once spring comes, the striped and spotted cucumber beetles feed from plant to plant, spreading bacterial wilt through the release of excrement. The bacteria from the excrements infect the host plants through wounds and the stomates. Then these insects feed from infected plants and ingest more bacteria, repeating this cycle. Upon infection, plants will begin to wilt and leaves will dry out. As the bacteria spreads throughout the plant, branches and vines will experience wilting. Eventually, they are likely to collapse and die due to heavy withering.
Bacterial Wilt Identification and Habitat
When identifying bacterial wilt, internal vascular tissue can be discolored to a yellow-brown color. The vascular tissue inside infected stems become dark brown or black as the disease develops. Throughout the bacteria’s development, the pith and cortex of the stem turn dark brown. Wilting is the most identifiable above-ground symptom of Bacterial wilt. Early in the season wilting will be most severe as plants are young and growing rapidly, allowing bacteria to spread very quickly. In the heat of the day, wilting is at its peak. However, some plants are seen to recover in overnight conditions. Large-leafed plants may only wilt on one side of the mid-vein (e.g. Nicotiana). Additionally, in many cases when vascular tissue is cut, bacteria will ooze out of the lesion in a sticky liquid form.
Commonly, Bacteria wilt will begin its spread in the spring when Cucumber beetles come out of hibernation. More specifically, Cucumber beetles tend to become active again once temperatures reach 55 F and above. Once the bacteria have infected a plant, it is very resilient and will spread quickly through the host, allowing the disease to develop in a variety of weather conditions. As previously mentioned, the bacteria will overwinter in the digestive system of the Cucumber beetles, allowing it to be spread once again in the next spring season.
Bacterial wilt Management and Control Methods
Although chemical controls are more common for Cucumber beetles, there are some cultural controls that can help to eliminate contact with these insects. Screens, cones, and row covers can protect small plantings from the beetles. Be sure to remove these protective covers prior to bloom to allow for pollination. These mechanical solutions can be effective for small plantings, but can be impractical for larger plantings.
Insecticides are the most common and effective way to avoid Bacterial wilt. Beginning an insect control program early is necessary to stop unwanted pests later in the season. After transplanting, a one-time soil drench using insecticides such as Admire or Platinum can provide protection for almost an entire season. When using insecticides be sure to read the label for safety tips and application instructions. Frequent applications of contact insecticides are very important to protect plants from beetles feeding. During peak beetle activity, applications twice per week may be necessary. The amount of applications necessary will depend on seasonal beetle populations.