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Foliar tomato diseases have been showing up in a few area gardens in the last few weeks so it's time to take precautions to keep these diseases in check when they visit your garden. I say when because if you grow tomatoes in Kentucky you will undoubtedly get foliar diseases.
The primary two diseases that I have noticed are early blight and septoria leaf spot. It doesn’t really matter if you know which of these you have but more that you have leaf spots that need to be controlled. These fungal pathogens cause dark spots in the leaves that gradually get larger; the leaf turns yellow and then dies. The fungal spores spread by wind and water splash and prefer a moist environment much like we have had for the last few weeks.
If you notice spots on your tomato leaves it is a good idea to start treating the plants with protectant fungicides such as products containing Mancozeb or chlorothalonil. These products come in concentrates that you dilute in water and spray on with a hand held sprayer. After a heavy rain the fungicides will need to be reapplied. Protectant fungicides cannot cure infections on already infected leaves but will contain the disease spread so as to prolong your harvest. Be sure to spray the lower and upper sides of the leaves. Before spraying pull off the infected leaves and destroy them, this will reduce the severity of future inoculation.
There are some cultural things you can do to help contain the likelihood of infection and the spread. First, if at all possible don’t plant tomatoes in the same location every year. Diseases can overwinter on plant debris and in the soil. Planting tomatoes back in the same spot is asking for trouble. Secondly, apply a mulch of some sort around your tomatoes, this will reduce the soil splash unto the bottom leaves and reduce the chances of early infection. Lastly, pull off the bottom most leaves when the first tomatoes set because by then the lower leaves are shaded and not photosynthesizing anyway and they are generally the first to get diseased.
If you have any plant questions give me a call at the Washington County Extension Office at (859) 336-7741. Happy gardening!