Blight on tomatoes is a fungal infection. This fungal pathogen is well known for its ability to produce millions of spores from infected plants under wet weather conditions that favor the disease.
Because the fungus 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 tomatoes is able to identify late blight and know how to control it. And,
Spores can travel by wind up to four miles; then land on a plant and infect it. So if a neighbor’s plants have the disease, yours may end up with it too
Theories abound on what actually causes the plant disease. Some say that soil which is nutrient-deficient creates a breeding ground for blight. Others say that a lack of lime is the problem. Finally, many successful gardeners insist that the fungus is bred by heavy rain fall, mixed with humidity and certain soil conditions. Regardless of the exact cause, blight can be detrimental to your crop.
Late blight has been present in the United States for more than 100 years, but it is occurring this year earlier and more widespread than ever.
How is blight treated?
The first step in stemming the spread of blight is to remove all of the damaged leaves. This is a painful process, but it must be done in order to keep the disease from spreading. Wash your hands in between plants so as to keep from spreading blight to healthy plants or leaves. Dispose of infected leaves away from your garden.
Blight lives in the ground, and by leaving infected leaves on the soil you will be furthering the spread. You will also need to plant your tomatoes in a different location for the next few years, as blight will continue to be present in the soil.
Next, you must purchase a fungicide that will halt the spread of the blight. Organic growers choose a natural, copper solution. Spray until the plant’s leaves are dripping with the solution. Though you should always read the directions carefully, you will probably be instructed to apply it once a week and after rains.
Copper is not as effective as chlorothalonil or maneb, but it is better than doing nothing. Applications should continue as long as weather conditions favor the development of late blight. Gardeners who want to spray organically could also use neem oil, but would have to reapply the oil weekly.
Petunias, which are closely related to tomatoes and potatoes, can also be infected by late blight and show similar symptoms.
Do you want to know more about how to fight late blight back?
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{ 9 comments… read them below or add one }
Tomato blight is a big problem this year in Connecticut. Thanks for this post – it’s a big help for how to deal with it.
I took down my plants in august due to blight. i was trying the “tomato ring” this year for the first time. I don’t have enough space to move my tomatoes 300 feet and I wish to resuscitate the area where they were. My father-in-law, a gardener of 50+ year, says I just need to lime it heavily after compost/manure application. Is that sufficient or should I do anything else? I am trying to be organic but two years w/o home-made sauce is too much to bear…
I think what your father-in- law says is very true. I would do exactly the same, lime the area heavily and then put a lot of compost
This is the second year for tomatoe blight. I have lots of tomatoes on the vines. Can I use the lime under the tomatoe vines now.
Thanks Curtis Harper
I already have lots of tomatoes on the vines. Also have tomatoe blight. Can I put the lime under the vines work into the soil now or will I have to wait until next year.
Thanks Curtis Harper
In France, the Bordeaux Mixture was created to treat fungal disease in vines. Consisting of copper sulfate and hydrated lime, this fungicide has been used for more than a century to control the infections that attack vineyards, nurseries, farms, and gardens.
I will do it now.
I have used H2o2 on my garden it helps a lot. This fungus is a major problem and I really don’t think it can be stopped. I can see the dead fungus on the plants but I fear it was to late. It was very hard to keep up with spraying this due to all the rain. Good luck and try some H2o2 (hydrogen peroxide) with your favorite spray mix it right in. Just an idea.
My garden has suffered with the blight for several years. I do the fungicide spraying and try to stay on top with removing the affected parts. I’m wondering if there is something to put in the soil in the early spring that will kill the fungus in the ground. In researching beneficial nematodes for the pecan weevil it mentioned that they can destroy fungus.Would this be a viable option? Thank you