![]() ![]() Remove the plant from the garden, place it in a trash bag, and throw it away. If it has grown mold, then you have late blight. If you suspect your plant has this pathogen, take a portion of the infected tissue (leaf, stem, or fruit), place it in a sealed bag with a damp paper towel. Concentric circles indicative of early blight, Okra In My Garden How to Test for Late Blight The best way to determine if a plant has early or late blight is to look for lesions with concentric circles since this is a tell-tale sign that occurs only in early blight. of Maine Extension How to Distinguish Late Blight from Early Blight While the lesions are firm, a secondary bacterial infection may occur that will cause the spots to become soft. The lesions have been described by some as looking “greasy.” The spots are circular and will eventually coalesce to cover large portions of the fruit. Infected fruit will develop dark, shiny lesions, usually on the top or sides of the tomato, as opposed to blossom end rot, where the lesions form on the bottom of the fruit. Progression of disease occurs rather quickly, and complete defoliation can occur in as little as one to two weeks. In advanced stages, other portions of the plant may have mold as well. As the infection spreads, the lesions on leaves and stems will turn brown and shrivel. The lesions may have a lighter colored halo or single ring encircling them.Īs the lesions grow, a white to gray mold will appear on the underside of the leaves. The spots will turn brown to dark olive green to black with a light green border on the underside. Tan to light brown, irregular shaped spots or lesions will develop, often near the tips of the leaves. The fungus attacks the plant through leaf stomata, so it is no surprise that symptoms first appear on the lower leaves. Regardless of the seasonal designations, late blight can occur anytime during the growing season when the weather is wet and cool. Phytophthora infestans is called late blight because it occurs later in the growing season, thus distinguishing it from early blight. While these are ideal conditions, the pathogen can produce spores in less-than-optimal conditions. Ideal conditions for infection and spread of this pathogen occur when there is high humidity, 90% or more, and temperatures are between 70☏ and 80☏ (21☌ and 26☌). It is the same pathogen that was responsible for the Irish potato famine that occurred in the 1840s. It primarily targets tomatoes and potatoes and, to a lesser extent, peppers and eggplant. Late blight is a fungal disease caused by the water mold Phytophthora infestans. Although the focus of this article is on tomatoes, the information can be applied to other members of the nightshade family, such as potatoes, peppers, and eggplant. In this article, you will learn how to identify, treat, and prevent late blight. Many people ask if they can “treat the soil” to get rid of such diseases, but most are not only soil-borne but also wind-borne so usually it’s not helpful to apply a fungicide to the ground.The three types of blight that most often affect tomatoes are early blight, late blight, and Septoria leaf spot. Next season mulch your plants as soon as you plant them so that no fungal spores will splash up on the foliage when it rains.ĥ. (Do not alternate these – the copper will kill the bacteria in the other two products.) Always start with the mildest of treatments for plants.Ĥ. Next season start spraying early first using something like Actinovate or Seranade, and switching to the copper once the plant has a problem. Although the fungicide won’t “cure” the problem it can protect the newer growth long enough so that tomatoes can be harvested. (In such cases I would use Actinovate, a natural bacteria.) Spray under the leaves and the stems too. If the garden is right next to a pond, lake or stream, however, do not use copper as it is toxic to aquatic life. Start spraying immediately with a copper fungicide – this is an organic treatment that is a bit stronger than other organic fungicides. Instead, water deeply less often, trying to do so in the morning so that the foliage has plenty of time to dry.ģ. This is a prescription for every leaf disease in the book. It’s amazing how many people routinely spray the leaves of plants every evening because they think that they are somehow “refreshing” the plant. Pull off the leaves that are spotted and/or yellow so the plant can be better monitored and some of the spores are removed.Ģ. ![]() That said, the treatment for the home gardener is the same:ġ. This could be bacterial leaf spot, early blight, late blight or another fungal leaf disease. There are several tomato plant diseases, however without culturing in a lab it’s hard to say which one is affecting your plants. ![]()
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