If you haven’t already started a fungicide program on your tomato plants this year, you may want to start. Last week I, along with most agriculture agents and horticulture agents in the state, received an e-mail from the Vegetable Plant Disease Pathologist from the University of Kentucky. Classic symptoms of late blight include large (at least nickel sized) olive green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid (early morning or after rain). Sometimes the lesions border is yellow or has a water-soaked appearance. Leaf lesions begin as tiny, irregularly-shaped brown spots. Brown to blackish lesions also develop on upper stems. Firm, brown spots develop on tomato fruit.
Now, if you have tomatoes and want to continue having tomatoes there are fungicides that can be sprayed to slow the spread of late blight along with many other foliar diseases on tomatoes. The difference with late blight is that it is very rampant and very devastating so fungicides need to be sprayed before infection occurs to get the best control. Also, if you aren’t sure you want to start spraying, I have one plant in my garden that I am 99% sure has late blight and I will be getting a confirmation from the pathologist this week. So, to be on the safe side you should apply fungicides now.
So, you want to know what to spray with right? Well, as homeowners there are basically three fungicides for you to choose from Daconil (active ingredient chlorothalonil), Maneb, and Mancozeb. You can use any of these and get adequate control. What I usually tell people is that these fungicides don’t completely wipe out diseases but holds them at bay to extend your harvest. When you stop your spray program and the weather is favorable they will again spread through your tomato patch. Be sure to get coverage over the entire tomato plant including the tops and bottom of leaves. Read the labels carefully for timing when you can re-enter the tomato area and for how many days you have to wait before eating tomatoes from sprayed plants. If you have any questions about tomatoes give me a call at the Washington County Extension Office at 336-7741.