As a result of the cool temperatures I am expecting a few phone calls about tomato problems. The first problem that is already showing up is the disease called septoria leaf spot. This is one of those tomato diseases that can wipe out tomato foliage if weather stays wet and humid.
Spots that are about 1/16 to 1/4 inch in diameter appear on the lower leaves first. This usually comes around the time of the first fruit set.
These spots have tan or blackish centers and are surrounded by dark brown margins. As the spots develop, the tissue surrounding them turns yellow. If there are a lot of spots on the leaf surface, the leaf eventually shrivels and dies.
The spots start on the lower leaves and work their way up the plant. If weather conditions continue to be favorable for this to continue developing, an enter plant can be leafless by the end of the season.
Tomatoes plants need their leaves in order to help produce good healthy tomatoes. Therefore, a heavy infestation leads to a reduced crop.
A minor infestation isn’t usually tolerable. The tomatoes themselves aren’t usually affected and they can still continue to grow and ripen.
Septoria leaf spot rarely affects the tomatoes but as I mentioned, it can be pretty hard on the foliage if wet humid weather continues. Recent heavy dews at night and humid weather during the day have been perfect for this disease to develop.
It is a challenge to control this and other tomato diseases due to timing of fungicide sprays as I mentioned last week in my column on the disease triangle.
In the past I have mentioned integrated pest management strategies and I have adopted some of these recommended strategies on my tomatoes and it seems to be helping (thus far, cross my fingers!).
Remove and destroy diseased leaves as you find them. If they remain in the garden, they are a source for continued infection.
Mulch around the base of the plants. This keeps the pathogen from splashing from the ground to the plants. I have found this to be very effective. I used newspaper and grass clippings, and so far things look good.
Don’t water overhead, rather use drip irrigation. If you don’t have drip irrigation, take the hose into the garden and lay it at the base of the plant and turn it to trickle for a little while at the base. Of course, we haven’t had to water this year yet.
Next year space tomato plants so that there is good air circulation to allow for leaf drying. And finally, use a fungicide spray to prevent future infection on the good leaves. Look for a fungicide labeled for tomatoes and the disease septoria leaf spot.
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