Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
As of Thursday, May 5, no Bacterial Fruit Blotch (BFB) had been confirmed in Delaware or Maryland. Please continue to monitor both locally grown transplants and transplants purchased from other areas, because BFB has been reported in Georgia.
Management of BFB in greenhouse plant production includes the following steps: 1) use seed that has been tested for Acidivorax avenae subsp. citrulli, 2) monitor plants for BFB symptoms, 3) if potential symptoms are observed, submit plants for diagnosis. If BFB is confirmed in a greenhouse, the symptomatic transplants and those in a 15-foot radius should be destroyed. Additional trays that are 15 to 20 feet from the infected plants should be removed and isolated in a warm humid location and observed closely for five days for symptom development. If symptoms develop, then the epidemic has not been contained and additional plants should be destroyed.
If, despite best practices, BFB is observed in a field following setting out transplants, BFB will continue to spread. The rate of spread depends on the environment and irrigation practices. Spread will be fastest in fields irrigated with a travelling gun, intermediate where center pivot irrigation is used, and slowest with drip irrigation. Likewise, spread will occur within a field during rainfall, especially during “driving” rains. Spread of BFB from field to field in air is not common (though the bacterium could move in an aerosol). However, spread from field to field will occur on tractors or truck tires, cultivation equipment, peoples’ hands and shoes, and other direct contact.
The best spray practices to minimize BFB spread in the field are to use copper and Actigard. Copper fungicide should be applied weekly beginning before flowering until after fruit set (approximately the first five sprays). Another option is to include a copper fungicide in the first, third and fifth fungicide application and include Actigard or Actigard plus copper in the second and fourth fungicide application. These programs have provided suppression (but not elimination) of BFB. Additional labor at harvest may be necessary to separate symptomatic fruit from symptomless fruit.