Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Bacterial brown spot was identified in pole beans as well as a commercial field of baby limas this week. Brown spot is usually only seen in wet seasons. The reddish-brown bordered irregular spots look very much like a fungus infection on lima beans. Levels of infection will vary with the heavier infections occurring in the lower canopy. Splashing rain will move the bacteria around as will cultivating when the foliage is wet. We have no data on effectiveness of copper fungicides to reduce spread or the potential for plant damage and yield reductions for this disease here in DE because it occurs so infrequently at this level of infection. It usually can be found at very low levels most years during wet periods. The bacteria are known to contaminate seed and be found on weed hosts where it can spread during rain storms to beans. Populations can be reduced on the plants with applications of fixed copper fungicides such as Kocide 3000, Champ DF, and others. The disease is caused by the bacterium Pseudomonas syringae pv. syringae.
Bacterial brown spot on baby lima bean