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LATE BLIGHT ALERT! (Extremely dangerous disease to tomatoes & potatoes...)

post #1 of 5
Thread Starter 

Hello everybody. I regret to have to post this but LATE BLIGHT is returning again this year east of the Mississippi, all the way north through Maine & Minnesota. I will post links here, some are from Cornell University, one of the leaders in Late Blight research; just because you don't live in NY or the Northeast doesn't mean you shouldn't worry or shouldn't bother reading--it is currently in almost every state east of the Mississippi right now! In southern states it can survive winters. If you have Late Blight (LB), please be a responsible gardener & take appropriate actions, as it is extremely contagious amongst plants in the Solancea family (taters, maters, etc.) LB to tomatoes & potatoes is similar to the Plague to Europeans in the 14th century. Some members of this forum had it last year too!


For weekly updates on NY & surrounding states, see  http://blogs.cornell.edu/lateblight/  I'm posting this site first because it has many other great links to the right side of the page.


For a Google spreadsheet of states/towns/areas infected for 2010, see the link below:



To read an article on how to avoid it and recognize LB, see http://blogs.cornell.edu/hort/2010/04/12/avoid-the-late-blight-blues/


For some EXCELLENT pics, see: http://www.longislandhort.cornell.edu/vegpath/photos/lateblight_tomato.htm


For a LB FAQs: http://www.hort.cornell.edu/department/Facilities/lihrec/vegpath/lbfaq.pdf


For LB MISINFORMATION Corrections, see: http://www.longislandhort.cornell.edu/vegpath/lbmisinfo.pdf


There is even a "RISK MAP" that has the US "stickpinned" with different colored pins (green, yellow, red) based on weather conditions and charts, though it takes some time to load fully: http://uspest.org/risk/tom_pot_map


Late Blight, not to be confused with Early Blight which many tomato growers get usually every year, is the same disease that caused the Irish potato famine in the mid 1800's. It can attack tomatoes, potatoes, and some weeds & flowers like petunias and others in the nightshade family.


Last year, the believed cause was infected plants sold at the big box & dept stores like Home Depot, Walmart, Kmart, etc, specifically anyone selling Bonny Plants. This year, while nobody is listing the cause, it appears to be the same strain, US22.


Late Blight is devastating and if you didn't spray approved fungicides regularly, especially from the start, it can turn a tomato garden into a pile of stinky mush in a matter of days. It also may take a few days to show signs of infection. It also affects not only the plants but the fruits (tomato is a fruit, not a veggie) and will rot them, starting with brown spots or areas on the tops. Late Blight makes spores in damp weather, dewey nights & mornings, etc, and the spores can travel great distances by wind. It needs a living host to survive and multiply. The heatwave many of us had has helped us, though let's hope it just didn't postpone the inevitable.


It's important to remember that it's much easier to PROTECT than to try to cure it, which is almost impossible without catching it in its early stages as well as using the proper fungicides.


The best fungicides are not organic, and the few organic products available have very limited success, if any. Copper is the most widely used organic fungicide. Neem doesn't work. Serenade only suppresses it slightly if you have been applying it early & regularly.


On the inorganic or non-organic list, look for fungicides that contain at least 29.6% Chlorothalonil as the active ingredient. Products are Daconil, Ortho Garden Disease Control, Fung-o-nil, etc, or commercial strength varieties such as Bravo, Equus, etc.


Other fungicides are somewhat effective which contain Manganes & Zinc, such as Mancozeb, Maneb, Manzate, etc. Strain US22 is susceptible to commercial fungicides that contain mefenoxam, such as Ridomil Gold Bravo, Ridomil Gold MZ, etc. None of these Ridomil versions are cheap, about $225 & up! For home use, Daconil, Ortho Garden Disease Control or Mancozeb are about $15 though.


For a good list of fungicides to prevent or control Late Blight, see this link:




If you have plants that match or exhibit the problems pictured, please contact your local county extension service or post pics in this thread to get verification or advice. Many here had it in 2009 but didn't know what it was or how serious it is.


For Late Blight "IMITATORS" see: http://www.longislandhort.cornell.edu/vegpath/photos/diagnose.htm Many things look similar and may be mistaken for LB.


I'm better prepared with some bigger guns this year to fight LB. My county has just tested positive. Hope everyone has a great tomato season!

post #2 of 5

Good info thanks for posting it. I'm on the left coast and this is my first real year attempting to grow a garden. Not long after getting my raised beds finished and planted I learned about Blight. It appears the fruitless maples in both my front and back yard have it. The expert at the local nursery is who told me it was blight but I don't recall him specifying a type of blight, early or late. I've been cleaning up the leaves on the ground like he suggested and so far my tomatoes are still doing ok.

post #3 of 5

Whatever your maple trees have, it is NOT the same thing that affects tomatoes and potatoes.  Late Blight, Early Blight, etc., are diseases only of the tomato/potato family.  Other families of plants can't get them, and stuff that affects other kinds of plants won't bother the potatoes and tomatoes.


post #4 of 5

FYI, Maine and other intensive potato growing areas have Late Blight every year.


The one place it can survive winters north of Florida is in potato tubers that had it last year and weren't properly destroyed.  There were a lot of those last year because last year's LB variety was one that hits tomatoes really hard and affects potatoes much less severely, so some growers either didn't realize they had it or were able to get a potato crop anyway.  So oddly enough, the very bad tomato LB has survived and reappeared from potatoes.  Ag officials in most states are attributing the initial outbreaks of LB this year to improperly handled cull piles of infected potatoes last year.


The main determinant of how widely LB spreads from year to year is the weather.  Last summer in the NE was ideal LB (and other fungal diseases) conditions-- cool and wet.  This summer's weather here is much, much better, LB showed up much later (last year it was all over the place by the end of June) and it won't spread as rapidly or as far.

post #5 of 5
Thread Starter 

Yes, that's right, the weather plays an important role. Late Blight is much more common in the Pacific Northwest, where it's often damp & rainy. LB isn't as common in NY though, and NY grows lots of potatoes here; I believe Long Island for example, only had LB 4 times in the last 20 years! As for Maine, I know lots of potatoes are grown there but I have lots of tomato growing friends there, as well as tomato & potato seed distributors in ME, but most haven't seen LB on tomatoes until last year.


I've been spraying regularly and believe I had LB on a few of my plants here. Someone was here from Cornell and took samples too. A customer about 10-15 miles south of me had a bumper crop of tomatoes waiting to ripen on a Friday and this on Tuesday:



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