Tomato Plant - Knowledgebase Question

San Diego, Ca
Question by mclaughlinso
October 25, 2009
My tomatoe plant develops white spots on some of its leaves and this eventually kills the leaves. I have cut off all the leaves and stems with white spots. Many healty leaves grew back but a few have developed the white spots again. What are the white spots and how can I stop them?

Answer from NGA
October 25, 2009


Powdery mildew can be a terrible problem once it gets a foot-hold in the garden! And because the disease overwinters on living plants, it is virtually impossible to eradicate. Here are some general rules for helping control fungal diseases. Start by making sure that your plants are getting enough direct sunlight. (Eight to ten hours a day is generally the minimum for plants that flower or bear fruit.) You'll also want to make sure that there's enough room between plants for air to circulate freely. Overcrowding not only makes plants more susceptible to diseases, if leaves touch other plants, those diseases can easily be spread. The general advice to inhibit the spread of fungal diseases is to avoid wetting leaf surfaces. In the case of powdery mildew, you can actually inhibit infection with periodic strong sprays of water (not so strong as to damage the plant.) After the new growth of affected plants reaches about six inches long and UNTIL THE TEMPERATURE REACHES 90 degrees F, you may apply dusting sulfur to foliage every 14 days. If necessary apply fungicide. Fungicide works much better as a preventative measure, before the powdery mildew becomes a problem.

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