The leaf in question. Notice the fuzz.
Late Blight is a bastard.
It took out my tomatoes last season, after herculean efforts to nurse them along and right when they were starting to turn. And for a moment last week, it looked like the bastard might be back.
On one leaf, on one plant, there was a single dark spot with white fuzz showing on the underside. Above it on the stem were black spots. On several other plants, leaves were browning around the edges.
“July is the month that gives us so much hope as the tomatoes size up and begin to blush,” said Petra recently as we walked the rows of tomatoes at the farm. “Only to be dashed into a thousand pieces in August by the blight.”
This isn’t hyperbole.
Late blight is a disease that looks a lot like a fungus but is actually caused by a pathogen more closely related to brown algae, Phytophthora infestans. Cool temperatures and moisture, both on the leaves and in the air, make an ideal environment for the disease. It spreads easily and can be airborne. It affects both tomatoes and potatoes; it caused the Irish Potato Famine in 1845. Once your crop shows signs of the blight, you can loose everything in just a few days.
There are three key steps to stopping the blight once you’ve positively identified it:
* Pull the infected plants. Bag them. Bury them or burn them.
* Spray the remaining plants with fungicide. Copper fungicides are approved for organic growing.
Other questionable damage.
It’s horticultural shock and awe. Heavy duty, no messing around. By solution or blight, you’re probably going to lose all your tomatoes.
Which is why it’s uber-important to correctly identify what’s ailing your plants. There are several other diseases and conditions that can be confused with blight, but don’t require the same heavy-handed response.
In comparison to the photos on the Cornell Cooperative Extension web site, the fuzz and the spots on my plant kind of looked like late blight. But I just wasn’t sure.
So I snapped my own photos and sent them by text and email to people way smarter than I am about these things. I waited for definite answers to roll in.
“Not to me,” said Jon, the first to respond. “Late blight usually wilts then turns black.”
“That looks like the early stages of late blight to me,” said Caroline, seconds later.
“The length and location of the spores looks more like gray mold,” said Caroline and Jon’s guy from Cornell Cooperative Extension. “But the color and texture of the lesion looks like late blight.”
“From what I see it does look like late blight,” said another guy from my own county’s extension office. “You cannot kill late blight.”
More questionable damage.
Definite answers? A whole bunch of “maybe” is more like it.
But in the course of all this communication, two very important details came up.
I mentioned to Caroline that the damage on my plants had been there for at least a week.
“Then it might not be late blight,” she replied. “It usually moves fast.”
Caroline’s guy at CCE also said something interesting: “If late blight, there should be more spots visible on the plant. Including fruit.”
There were no additional spots on the plants. And absolutely no damage whatsoever on the tomatoes themselves.
And it was these two details that helped me decide not to nuke my plants.
Instead, I just cut off the affected leaf and any other questionables: snip, bag, tie, and leave in the sun to die. If this really was blight, all my tomatoes were dead anyway; I only have seven plants growing in close proximity to each other. Taking this extra step wasn’t going to make things any worse. But if this wasn’t blight – or if I had caught it early enough to make a difference – then I had just saved my little tomato crop.
The tomatoes look great.
The gamble paid off: eleven days have passed and there’s been no recurrence of dark spots or fuzz. The damage around the leaf edges hasn’t spread. The fruit looks beautiful; the Gardener’s Sweethearts, Black Cherries and mystery tomato continue to turn.
It’s important to point out that Caroline and Jon run their own farm plus a winery. They took time out of their busy day to help me solve my problem. I am extremely grateful to have such good people in my community.
Of course, just to prove that no good deed goes unpunished, one week after Caroline and Jon helped me work through my uncertain situation, their own crop of tomatoes was identified as having blight.
“The plants are all dead even if they don’t know it yet,” said Caroline. “We hopefully saved the potatoes by mowing off the tops.”
Did I mention that late blight is a bastard?
Jon Hunt and Caroline Boutard-Hunt, Italy Hill Produce, http://www.huntwines.com/Italy-Hill-Produce
Petra Page-Mann, Fruition Seeds, http://www.fruitionseeds.com
Long Island Horticultural Research and Extension Center, Cornell University, http://www.longislandhort.cornell.edu/vegpath/photos/lateblight_tomato.htm
USABlight. What is Late Blight? Retrieved from http://usablight.org/lateblight