|My tomato plant has white spots on some of the leaves. The spots look chalky in appearance, and seem to be spreading. A few stems may also be affected, but the spots are mostly on the leaves. What are these spots and what should I do about them? My tomato plant is in a large pot of regular potting mix and has grown to approx. five feet tall. It currently has 6 green tomatoes on it. Please advise.|
|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. There are some things you can do to minimize its effects.
Powdery mildew is unique among plant diseases in that it doesn't require a wet leaf surface to spread. It can thus thrive during hot, dry weather. The first line of defense is to grow resistant varieties. Next, remember that while the disease is unsightly, it doesn't cause any real harm to many of its victims (though it will damage some plants.)
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.