problems with my zucchini and tomato plants - Knowledgebase Question

oswego, Il
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Question by carter218
August 15, 2010
my plants always seem to get powdery mildew and the tomato plants get yellow spotted leaves. I have tried spraying the leaves with a fungicide, but it hasn't helped. It seems to happen every year. What can I do to prevent this? Looks like my plants are all dying.

Answer from NGA
August 15, 2010
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. Crop rotation - planting in different areas of the garden each year - can go a long way in helping protect your tomatoes and zucchini. There are some other 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 can eventually 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 so you need to make applications early in the season before you see evidence of the disease.

There may not be anything you can do for your plants this season but if you choose disease resistant varieties and plant them in a different spot in the garden next year, and if you begin your protective fungicide sprays early in the season, next year's plants should remain healthy for you.

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