Bacterial Wilt of Southern Highbush Blueberry

Bacterial wilt of southern highbush blueberry caused by Ralstonia solanacearum

By: Phil Harmon, UF/IFAS Extension Blueberry Plant Pathologist

Bacterial wilt is a newly discovered disease of blueberry in Florida. Symptoms of the disease are similar to those caused by Xylella and bacterial scorch. Plants with bacterial wilt will show signs of water stress such as wilting and marginal leaf burn. Symptoms can quickly become severe and can kill plants in as little as three weeks in inoculation trials. Plants may also be prone to develop severe symptoms of other stress diseases such as stem blight in the affected patches and may show symptoms of both diseases. Crowns of blueberry plants with bacterial wilt have a mottled discoloration or light brown to silvery purple blotches with ill‐defined boarders (Fig. 1). This discoloration is distinct from that which occurs with stem blight disease, because stem blight discoloration is typically pie‐piece‐shaped and pecan brown in color. Additionally, wood chips floated in water from crowns of plants with bacterial wilt will stream bacterial ooze, Fig. 2. Stem blight infected wood chips do not.

Unlike Xylella which causes bacterial leaf scorch, this bacterial pathogen can be spread easily in water, soil, or through infected plant material. Plants can be infected without showing symptoms. Ralstonia can survive for years in soil, slowly spreading down and across rows of blueberry leaving large circular patches of dead and dying plants (Fig.3 + 4) similar in appearance to Phytophthora root rot affected areas, but not necessarily only in low‐lying and poorly‐drained soils. The pathogen is efficiently spread in recycled irrigation water and in ponds used for irrigation once introduced to a farm or nursery facility. Ralstonia can also be moved on pruning and other equipment from plant to plant once established.

The disease has initially been confirmed on three farms, two in Desoto County and one in Lake County in Florida. On all three farms, the variety Arcadia was the most severely affected. Other varieties may also be susceptible, but additional research is needed before we will know for sure. Although this is the first time the disease has been confirmed on blueberry in Florida, populations of the pathogen are common in Florida on other hosts. Ralstonia solanacearum causes diseases on a wide range of other plants including geranium, tomato, potato, peppers, and several other weedy, ornamental, and crop plants. We don’t know why it has only now been found causing disease on blueberry. There has only been one other case of bacterial wilt on highbush blueberry known, and that was confirmed on a single farm in New Jersey in 2012 by scientists at Rutgers.

To manage the disease, first make every effort to keep from introducing the bacterium onto your farm. The risk of introduction can be reduced by limiting movement between farms of soil or infected plant materials on equipment and workers tools such as tractors, pickups, pruning shears, etc.. Mud transferred on vehicles during freeze protection from farm to farm is another possible mechanism. Purchase and use only healthy plants free of disease.

Second, remove and burn or bury infected plants where the bacterium is detected. Then, use soil drenches of products with phosphorous acids or salts to help protect surrounding plants from infection, and prior to replant. K‐Phite is an example that is labeled for blueberry and for soil drench or chemigation application for Ralstonia control. For chemigation application through drip, use 2 to 4 quarts in at least 200 gallons of water per acre. For an application to soil, use 2 to 4 quarts in a minimum of 20 gallons per acre then lightly apply overhead irrigation after application. Potted plants can be drenched with a solution of 2 to 4 quarts of K‐Phite in 100 gallons of water prior to planting into fields where the disease has occurred. On other crops, this method has successfully protected plants from infection. Follow‐up applications made according to the label are also recommended and can be made on a 7 to 28 day interval. Similar alternative products are available from other manufacturers.

Injection or soil applications are recommended at this point for the variety Arcadia wherever planted and for all varieties on farms where the disease has been confirmed. Send samples of Arcadia showing wilt, scorch, or plant death that moves down rows through your county extension agent, or directly to the UF/IFAS Plant Diagnostic Center in Gainesville for a diagnosis. Plants that are sampled from the affected areas should be sick but not dead, and we need a fresh crown to test, so use an overnight or two day shipping option. The lab is covering the diagnostic fees for culturing and PCR to support the delimitation and management strategy. The address is below, and include a sample submission form that indicates the plant location and variety, and the need for bacterial wilt testing. Call the lab with any sample or shipping questions; test results will be emailed to the sample submitter and the blueberry pathology Extension specialist.

Direct questions concerning bacterial wilt to the state blueberry pathology Extension specialist Dr. Phil Harmon: office phone 352 273 4622, and email pfharmon@ufl.edu.
Diagnostic Center website:
http://plantpath.ifas.ufl.edu/extension/plant‐diagnostic‐center/
The form: (http://plantpath.ifas.ufl.edu/media/plantpathifasufledu/plant‐diseaseclinic/PDC_Submission_form_CC‐1.19.16.pdf)

Dr. Carrie Lapaire Harmon, Director Plant Diagnostic Center
UF‐IFAS Plant Diagnostic Center
Bldg. 1291, 2570 Hull Road
Gainesville FL 32611
352‐392‐1795
pdc@ifas.ufl.edu