removing fungus causing septoria on tomatoes
I have a raised garden bed in which I grew tomatoes this summer. They became infected with septoria, the leaves fell off and very few tomatoes were harvested. I would like to prevent this from happening next summer. The bed is 4x4. about 3 feet off the ground and filled with potting soil. A soaker hose buried beneath the soil watered the tomatoes. The lower leaves were removed from the plants when planted so that no plant part touched the soil.
I would like to put something on or in the soil this fall to prevent the fungus from returning next spring. Is there anything available that will serve this purpose? I am physically (and financially) unable to remove the soil and refill the bed with new soil.
Barry County Michigan
My first thought is, "Are you sure it is Septoria leaf spot?" It could be, but a more likely candidate is early blight. Both are fungal diseases and can be controlled using products containing chlorothalonil. This not an organic product if you are growing organically. I assume you are not growing organically since you are looking for something to apply to the soil to control.
Both diseases will overwinter in plant debris so your first step is to remove all plant debris from the area - remove plants, rake out leaves etc. Both diseases travel from the soil to the plant via rain splash and then move around from leaf to leaf by subsequent rain splashing. Your first line of defense is to cover the soil with a mulch of some sort to create a barrier between the soil and the plant. This will not eliminate the disease but it will slow spread. After planting, spray with the chlorothalonil product on a 7 to 10 schedule, especially before a rain. There are no products you can drench the soil with to eliminate the diseases.
If you keep planting tomatoes in the same spot year after year, you will eventually develop other disease and nematode problems, primarily Fusarium and verticillium. Continued planting of tomatoes and tomato relatives is not recommended.