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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