October 2009. A missionary based in a remote part of the Southern Highlands Province, Papua New Guinea, brought diseased bananas to Aiyura Research Station. What is likely to have caused the symptoms?
The large lesions are very typical of Cordana musae; it normally enters where there has been some other damage to the leaf such as insect damage, black leaf streak or (yellow Sigatoka in Australia). As far as control goes the best thing would be to remove the most severely infected leaves before applying fungicides, if that is warranted - probably mancozeb + oil would be sufficient and the cheapest.
The symptoms on the other photo are a little different, as it appears to be more of a marginal burn, which could be related to nutrition. The other possibility would be Black leaf streak, Mycospharella fijiensis. Has Panama disease (Fusarium oxysporum) been recorded in that area?
It was thought that the general yellowing of the second photo was a little unusual; however, it could be a reaction of the genotype to Black leaf streak. There is a need for closer shots of the lamina to see whether there is an association of early stage leaf streak symptoms with the yellowing.
Planting under partial shading helps reduce Black leaf streak, and so does sanitation – removing old infected leaves and setting them on the ground upside down so the spores produced mostly on the topside are discharged toward the ground. Removing infected leaves with more than 50% infection is recommended. More open spacing between plants helps dry the leaves, providing less time for infection.
Stem rot (Marasmiellus inoderma) has also been reported from survey done in different parts of PNG, and causes yellowing of the leaves. Stem rot is promoted by poor garden management (weed growth, no desuckering and no removal of trash). Disease management consists of ensuring planting material is ‘clean’, plant density is low, there is regular desuckering and removal of trash, and weed are controlled. It also involved correcting nutrient deficiency and providing good drainage.