Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Gummy stem blight was diagnosed on watermelon and cantaloupe transplants this week from Sussex County. Nancy found abundant fruiting bodies of the fungus and plenty of spores. The cotyledons were black and the fungus had infected the stems on some plants. If these transplants are set out, most of the infected plants will die but not before possibly producing spores that could infect nearby plants that might not be showing symptoms. Fungicide applications in the field would be strongly recommended if you suspected or had confirmed infection on transplants. Normally we would suggest a band application of chlorothalonil (Bravo) as a preventative but with the possibility of high disease pressure a combination of chlorothalonil and Pristine would be suggested. In situations where there might be suspected resistance issues with Pristine or reduced activity with Pristine, there are two other products that are labeled for gummy stem blight but are not in the recommendations book since we have seen little data in the region. A fall test in SC in 2008 conducted by Dr. Tony Keinath at Clemson University showed very good control of gummy stem blight under heavy disease pressure with Folicur and Switch. Both products were alternated with 2 pts of Bravo after two applications of either fungicide. This is only one test but the results were significant. With the weather being what it is, alternating Pristine with one of these products may be an effective alternative.
Two gummy stem blight infected transplants and a healthy one on the right.