If survivors any do come up in spring, pull them out right away and wait a few days before planting potatoes or tomatoes in that spot. Also, leave the bed itself exposed to the cold of winter and certainly don’t mulch it, as that could protect any unnoticed tubers. To eliminate this source of infestation, try to clean up the potato bed thoroughly in the fall or leave any debris on the surface where cold air ought to kill any survivors. Volunteers too can easily harbor potato blight. They frequently survive in mild climates, but also in protected spots in cold ones. That’s the term for potato tubers that people accidentally leave in the ground over the winter and that resprout the next year. The second way late blight can survive from year to year is from from volunteer tubers. And this disease should be so easy to prevent. Not only are you spreading this disease to your own potatoes and tomatoes by keeping starts, but to your whole community as well. At least when certified disease-free plants are readily available, like potatoes, raspberries and strawberries. If there is one situation where you really need to buy fresh plant material rather than grow your own from scratch, it’s with plants prone to serious diseases. However, this is one case where I disagree. Usually, I’m all for DIYing, recycling, reusing, saving “annuals” from year to year, etc. However, many gardeners grow their own potato starts from untested tubers … and thus cause a huge problem, both for themselves and for their neighbors. Because, in most countries, any seed potatoes sold have to be certified free of late blight and other diseases. This would be easy to solve if gardeners always bought their seed potatoes rather than grew their own. According to several studies, this is by far the most common means of transmission in temperate climates. And if it’s infected, it spreads the disease when it sprouts, because the spores can be carried several miles (kilometers) by the wind. So, they cut up a tuber from the previous year into sections, each with an eye. The most common means of transmission is when gardeners use leftover spuds from the previous year as seed potatoes the next spring. Potatoes usually survive the winter in two ways, plus a third more theoretical one. Some do survive … then release millions of late blight spores the next season. And if all tomatoes usually die in the winter, that’s not always the case with potatoes. It’s not at all unusual for related plants to share the same diseases. Yes, the disease that caused the Irish potato famine! And, true enough, the two plants, the tomato ( Solanum lycoperiscum) and the potato ( Solanum tuberosum), are closely related, belonging to the same genus: Solanum. But there are a few ways around that limitation and they’re enough for late blight to come back year after year.įirst, it’s important to understand that late blight ( Phytophthora infestans) is actually the same disease as potato blight. Since late blight only overwinters on living tissue and tomato plants die in the winter, that should solve the late blight problem quite neatly. Where tomato late blight overwinters In temperate gardens, late blight is mainly transmitted by infested potato tubers used as seed potatoes in the spring. Any tomato bits will still be dead, and therefore any mildew will be too. This will also be the case with a compost bin where the tomato residue may not have completely decomposed by spring. And dead plants can’t transmit this disease. Even if there are still roots, leaves or fruit on the ground in the spring in fact, even if they haven’t yet fully decomposed, they’ll still be dead. And, except in tropical regions where the tomato acts as a perennial vine, tomato plants die at the end of the season. This disease can only overwinter as mycelium in living tissue. You see, soil and pots simply don’t transmit late blight disease ( Phytophthora infestans), currently most serious tomato disease in many areas. You needn’t worry about the soil contaminating your tomato plants, because it simply doesn’t carry late blight! Should I throw out the old soil and start over with fresh soil? And how do I to sterilize the pots? I’m not even sure you can sterilize fiber pots.Īnswer: Actually, you don’t have to do any of the things you suggested. However, I’m now afraid of spreading the disease through the soil. I would normally have reused last year’s soil, just mixing some compost to aerate it a bit. Question: I had late blight on my tomato plants last year that I grew in fabric pots. You can’t blame contaminated soil for its reappearance the following year. Tomato late blight only overwinters on living tissue.
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