As many of you will know, thousands of SSA smallholder farmers are growing Jack beans to re-fertilize their soil. And hundreds are forced to eat their JB plants as they have no other food!
Imagine their consternation when told that some plants in Uganda have been attacked by a fungus!!
I can find only one case of this - in Brazil - with no remedy!
Can anyone suggest a possible solution??
Graham Knight
BioDesign
biodesigndiy@gmail.com
Southern Blight is endemic in the warm and wet areas of the world. The only sure answer is to stop growing the susceptible plant variety. Not very pleasant advice, I know. Since the question is usually what does Southern Blight NOT infect, the alternatives are few. Maize is the obvious one. But the rotation has to be a long one and it has to be accompanied by other measures such as the keeping of the infected ground as dry as possible, hoeing and burning on-site of all other growing material, implement and boot and hand-washing, using pig manure in large quantities, subject to the pH of the soil infected, applying lime or calcium nitrate to the maize. It is a nasty business.
Really, leaving the infected land alone and cleared of all growth for 4 years or so would be ideal but in SSA that is clearly not an option if there is no alternative site.
There are the usual fungicides such as captan and thiophanate methyl but they have to be applied long before the infection occurs and they are not a complete cure. Solarization can work a little prior to planting but the fungus always comes back. Really, apart from planting of maize for as many seasons as possible [ I know, it brings its own problems] the answer is to go for reduction of infection rather than elimination.
What about improving aeration? Wouldn’t that help? If you prune the beans you get mulch and a plant that has more air penetration which should help prevent the blight. Mulch or fertility enhancement is an important byproduct from intercropping with Jack Beans. When you cut back the plant you are also causing it to slough off roots which mineralize quickly and release their nutrients to the ground where it is available to the intercropped crop. You have to be careful how you prune though… If you prune them the wrong way (such as slashing the top) you may make the plant denser and take longer to set pods and increase the blight.
Yes, aeration would certainly help. I don’t think it would actually prevent the disease. Also, you can see the fungus spreading on mulch material. On the whole, I think it is best to do all the reduction strategies but learn to live with some of the fungus appearing. If it is a wet site then the fungus may become more of an issue. Luckily, we have a fairly arid site inland. Maize rotation and other small grains in rotation will work to reduce severity. I see now that there are some resistant varieties of tomatoes and peppers so one could use them in the rotation. However, even resistant varieties will in due course succumb. Thanks for your insight.
