May 2014. A member from Pohnpei, Federated States of Micronesia, asked for help in identifying a disease of cucumber. He was asked to inspect cucumbers on Pohnpei, and found damaged leaves that he thought were gummy stem blight on the stems, Didymella bryoniae, and asked wither it is likely to be the cause of the problem? The farmer has been growing cucumber on the same land for several years.
The photo was not clear enough for a diagnosis; a long shot to see the general state of the plants was needed, but none could be obtained as the farm was some way off. Photos of gummy stem blight on cucumber taken in Pohnpei in the 1980s were sent (top right & left below).
There was a suggestion that the damage was caused by snails!
Another suggestion was bacterial wilt of cucumber which is transmitted by beetles. To check, another visited to the field would be needed to inspect the stems. If a stem is broken and a stringy goo is present, this is indicative of bacterial infection. If this was the case, it is likely that the plants would collapse. Copper sprays might be useful.
Also, it was suggested that important steps in managing the disease are to:
- avoid continuous cropping
- destroy residues
- use a seed treatment
A fact sheet from Hawaii (http://www.extento.hawaii.edu/kbase/crop/type/d_bryon.htm) mentions that reports of gummy stem blight being seed transmitted are conflicting, but there is good evidence for it from other sources (muskmelon and cucumber/pumpkin).
The sender of the message from Pohnpei also asked about spreading Mancozeb, as a paste, with a brush on the stem against gummy stem blight. Is this a recommended application? It was not thought to be a technique that would help! Better to have resistant varieties if they are available, and the writer said that he would contact AVRDC. A fact sheet from the University of Florida was sent to help.