Answer: Late blight is a common disease of tomatoes, caused by the fungus Phytophthora infestans. Cool, wet weather favors disease development, and the fungi stay on infected stems during hot, dry weather, waiting for weather to cool down so it can sporulate. To avoid the disease, rotate your tomato crop to another area of the garden each year. Remove and destroy tomato plants at the end of the season. (Don't compost them, and don't allow volunteer tomato plants to sprout in your compost pile.) When planting next year, provide adequate space between plants, and prune leaves to allow good air circulation within each plant. Avoid wetting the foliage when irrigating. Try growing tomatoes next to the foundation of your house where eaves will keep rainfall from getting the leaves wet, or construct a canopy over the tomato bed to keep moisture off the leaves. Better luck with your tomatoes next year!
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