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 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!