![]() ![]() Examine your seed and your tomato transplants carefully before you buy and plant them. Certified seed is not a guarantee that late blight will not be present, however. Many states where potato seed is produced have seed certification programs to ensure that the seed meets certain standards for disease levels. One important way to avoid introducing late blight on potatoes is to plant healthy certified seed potatoes. Potato tubers or tomatoes (transplants or imported fruit) are a source of early season spores. In a few weeks you should see the plant responding. Side-dress with blood meal and water in thoroughly. In concert with routine spraying of the appropriate fungicide (see below) and maintenance pruning, you may find you need to stimulate your plant to generate leafy growth to replace diseased leaves you’ve removed. That’s a trick, I know, put if you stick to taking only the worst infected leaves off at any one time and staying within the 30/70 rule (never remove more than 30% of the leafy canopy a week), you should be ok. ![]() Prune away infected leaves as much as possible without over-pruning. Thoroughly clean your tools after working on an infected plant and at season end (soak in 9 parts water to 1 part bleach, rinse well and dry completely)! If you are stepping on soil that you suspect might be infected…clean your shoes! The most effective management strategy for late blight is to avoid sources of early season spores.ĬLEAN, CLEAN, CLEAN! Blight, depending on the type, can survive on living or dead plant tissue and in the soil or compost pile for over a year so practice good soil hygiene! Do a thorough end-of-season garden clean up and bag and dispose of any remnants of diseased plants (do not compost!). ![]() But…if you’ve been gardening with me for awhile, you already do this! Make sure you’re routinely adding plenty of organic matter to your soil which is teeming with ‘good’ fungi that can counteract the ‘bad’ fungi. On tomato fruit, late blight causes a firm, dark, greasy looking lesion from which the pathogen spore producing structures emerge under humid conditions. Symptoms on tomato leaves and stems are similar to those on potato. Spores can also be washed through the soil to infect potato tubers, which may rot before harvest, or later in storage.īecause the pathogen that causes late blight produces so many spores, and the spores can travel long distances through the air, it is very important that everyone who grows potatoes or tomatoes is able to identify late blight and know how to control it, to avoid being a source of spores that infect potatoes and tomatoes in neighboring gardens. Spores produced on infected potatoes and tomatoes can travel through the air, land on infected plants, and if the weather is consistently moist or wet, cause new infections. Temperatures consistently above 86 degrees have been shown to be unfavorable for late blight. Early in the season, the disease can be introduced into a garden on infected seed potatoes, from volunteer plants growing from diseased potatoes that were not harvested last season, compost piles, or infected tomato transplants brought into the area. All parts of the plant are affected including the fruit which can manifest as greasy, gray spots that spread quickly. This organism is well known for its ability to produce millions of spores from infected plants under unseasonably cool wet weather conditions that favor the disease. It is caused by the fungal-like pathogen, Phytophthora infestans that survives from one season to the next in infected potato tubers and tomato transplants as well as dead potato and tomato vines. It is the same disease that lead to the Irish Potato Famine in the 1840s. This is a very destructive and very infectious disease that is significant in potatoes (not sweet potato) but also occurs in tomatoes. ![]()
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