Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Earlier this year, Nathan Kleczewski alerted all to a “new” bacterial disease of potatoes that is similar to, but more aggressive than black leg. He wrote an excellent article on the disease for the WCU on April 1 http://extension.udel.edu/weeklycropupdate/?p=8900. During the past week symptoms of black leg have shown up in potatoes in Delaware and Maryland. Samples have been collected and sent for diagnosis of the bacteria. We strongly suspect that it will be confirmed as Dickeya dianthicola. At this point in the growing season, there is little that can be done to prevent or manage the disease. However, growers should avoid excess irrigation and have a balanced fertility program. The following is a list from Nathan’s article on what to do if you have confirmed Dickeya in your field:
If you have symptomatic fields and D. dianthicola is suspected/confirmed:
- Harvest these fields last
- Disinfest equipment with quaternary ammonium. Typical sanitation products such as bleach will not work against Dickeya spp.
- If potatoes are to be stored, ensure rooms are adequately ventilated and are maintaining cool temperatures
- Avoid including brassicas or onions in rotations
- Manage volunteer potatoes
- Avoid placing cull piles near fields or production areas
- Check your seed certificate
Photos below are potato samples from Maryland and Delaware. Note darkened aerial stem lesions (Fig. 1) and lesions emanating from the soil line (Fig. 2).
Figure 1. Darkened aerial stem lesions
Figure 2. Lesions emanating from the soil line