Kate Everts, Vegetable Pathologist, University of Maryland; firstname.lastname@example.org
There has been a report of a bacterial seedling disease on muskmelon ready for transplant this week. The sample in question turned out to be angular leaf spot (ALS) caused by Pseudomonas syringae. Recent research from University of Florida demonstrated that populations of P. syringae that cause ALS are very diverse. It isn’t uncommon to see this disease every few years in Maryland and Delaware. Our experience has been that if infected plants are transplanted to the field and the weather turns hot and dry, damage due to ALS may be minimal. However, prolonged cool and wet conditions will result in losses.
If conditions favor disease development, apply the labeled rates of fixed copper plus mancozeb. (Some coppers are OMRI-approved and may be able to be used in organic systems to help suppress ALS.) Continue applications at weekly intervals. In addition, to reduce ALS spread, avoid overhead irrigation when symptoms are present and avoid working in field while foliage is wet.
Nathan Kleczewski and I wrote an article a few years ago about several greenhouse diseases that occur during transplant production. The link to that information and many images of these seedling diseases can be found at: http://extension.udel.edu/weeklycropupdate/?p =6727