![]() ![]() The disease just advances too fast for any recovery. Sadly, once a tomato plant has serious symptoms of late blight it rarely bears good fruit. Stem lesions are a sure sign of late blight That's a sure sign, because other typical causes of brown leaves won't make the stems look that way.īrown spots on the leaves usually have fuzzy white margins When late blight starts to advance in tomatoes, it almost always shows brown-black stem lesions.If you don't see the white growth in the image here, it might still be late blight, but maybe not. Those are the new spores getting ready to infect your whole garden. If the brown spots on the lower leaves are caused by late blight, they will probably have fuzzy white margins.There are other tomato diseases that are not fatal. Still, before you get too alarmed, there are lots of reasons why leaves can turn brown. ![]() That's enough to cause browning leaves, horrible stem lesions, and browning tomato fruit on all parts of every plant, in just a few weeks. Spores can be produced in as little as 5 days under those ideal cool, wet conditions, so before you realize what's happening, you can have two or three generations of infection. The brown spots are colonies of late blight fungus, which produce spores and release them into the air. If the fungus spores are in the soil, you'll first see late blight spots on the leaves in the splash zone at the bottom of the plant. Usually, it gets there when rain splashes soil up onto the leaves (though driving rain or windy mist can carry spores from other infected plants). Late blight starts with little brown spots on the lower leaves of your tomato plants. In the case of late blight, the fungus has been given its favourite conditions: cool nights in July, even when those same days have been unbearably hot. So no matter what temperature a particular disease prefers, it's more likely to get it. Under climate change, the temperature moves further up and down in both directions. Sure, there have been a lot more hot days in recent years, but there have also been a lot more cool nights. We're not just experiencing global warming, we're experiencing greater fluctuations of temperature from hot to cold and back again. This is the hidden danger of climate change. In years past, midsummer nights tended to stay warm, so blight would spread slowly, but recently we've had a lot more fluctuations of temperature and rainfall, causing more wet, cool nights during July. But it prefers to do that when temperatures are cool, and the plants are wet. Once the fungus has infected a tomato plant, it can multiply to infect others. Now, the disease comes back year after year, because the new strains can live in old plant tissue, even frozen.Īnother part of the problem might be that we're getting more late-blight-loving weather. Old-fashioned late blight was killed by cold temperatures, so it might have been carried into your garden on an infected potato or tomato seedling, and caused its massive damage that season, but it would die out over winter. Part of the problem is that new strains have appeared during the past ten years that are able to overwinter in our cold climate. Late blight is showing itself in tomatoes and potatoes more than ever during recent years. It's the fungus that caused the Irish Potato Famine, and it's been found throughout North America wherever potatoes and tomatoes have been grown (remember, those plants are originally from the Western hemisphere so their diseases were around here long before they appeared in Ireland). Late blight has been around for a long time, mostly causing problems for tomatoes and potatoes. This is a disease that has caused catastrophe, been despised by history, and is fittingly named in Latin: Phytophthora infestans, literally the "Attacking Plant Destroyer". Then within a few weeks it destroys everything: the leaves, the stems, and the tomatoes. It's a disease that comes late in the season, after you've invested lots of work in your beautiful tomato plants, and it starts as a few little brown spots that you probably won't notice. Of all the problems that can affect tomatoes, late blight is the most heartbreaking. ![]()
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