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July 10, 2009

Tomato blight warning

late tomato blight

 Photo courtesy of AVRDC/The World Vegetable Center

University of Maryland agriculture officials are asking vegetable gardeners in Maryland to be on the lookout for late blight, a serious fungal disease that afflicts tomatoes and potatoes.

The Plant Diagnostics Lab received a suspect sample from a Howard County garden in June and found it to be infected.

Despite the name, late blight can occur anytime plants are actively growing and is especially damaging during cool, wet weather, which we have had plenty of.

It first appears as dark, water-soaked spots on leaves. The leaves quickly shrivel and die. Dark brown spots also appear on plant stems. The disease can be slowed by hot, dry weather.

Infected tomatoes can have shiny, dark or olive-colored lesions that may cover large areas. The infection can produced a foul odor as well

This is the same blight that caused the famous potato famine in Ireland in the 1840s, and can be particularly destructive in home gardens.

It is possible that the blight, appearing this early and with such a potential to spread, might effect the quantity and price of tomatoes this season. Usually, the blight hits plants late, after most of the fruit has been harvested.

Here are a few tips for dealing with the blight, courtesy of the University of Maryland Home and Garden Information Center.

  • Keep foliage dry. Avoid overhead watering. Avoid crowing plants.
  • Always purchase new need potatoes that are certified "disease-free."
  • Do not compost store-bought potatoes and don't store infected tubers.
  • Pull out and destroy all infected plants.
  • Keep developing tubers covered with soil.
  • Place infected plants or fruit in a sealed bag and dispose.
  • Protectant fungicides like chlorothalonii and fixed copper can help protect foliage if applied prior to infection.
Posted by Susan Reimer at 12:56 PM | | Comments (8)
Categories: Garden diseases


Comments? What? And admit we bought some of these from the Big Box Stores! We planted tons of them at great expense! If we keep quiet, this plague might just pass us by....
Grandbobs Garden

If you are suffering from this blight this year, it is very late in the game to recover from. It is reported that a corn & garlic spray may be effective in helping retard the fungus. Here is how to make and apply such a spray:

Gather a handful of corn leaves leaves (any kind) and as much of the papery outer leaves of garlic as you can. Process thoroughly in a blender. Mix with sufficient water to make a thin liquid. Let sit for an hour, strain and spray on plants. Never spray in full sun. Late in the day after the plants are out of the sun is the best time to apply.

As a "tip" for next year's tomatoes - buy locally grown starters or even better yet, start your own from seed. This year's blight, especially in the East appears to have been at least partly perpetuated by plants that were mass produced and carrying the blight and then sold through several of the "big box" store chains.

Hope this helps and good luck!

I think you mean "affect" not "effect" in the third to last paragraph. Easy mistake.

Affect is a verb and effect is a noun.

there is plenty said about what the blite does or looks like, i know what it goes, what i want to know is there a product on the market that i can spread on my garden over the winter to kill the fungas? i dont want it to reapere next year cause i had it in the ground.

Good question Ed, I will check into this.

I know that this is late, but I wanted to reply to the question on concerning the fungus over wintering. Late blight (from what I understand) will only live in living plant tissue. The only way that it will overwinter is if you have infected potato tubers in the ground. Even then, weather conditions have to be right for it to show up again. Remove all volunteer potatoes and you should be fine.

That's what I understand, too, Shirley. --Susan

I have a container garden outside on my deck that I have been growing tomatos in. Last year only one of my plants got the blight but this year its both. I'm wondering if this could have survived in the soil through the winter from last year or if it's airborne. Does anyone have any suggestions on what I should do with the soil next year? Should I get rid of the soil and start with fresh soil or will this not help at all because its floating around in the air. How many seasons might this last?

Chuck, it's a pain, but I always start fresh plants with fresh soil. It seems that container growing really depletes soil of everything that it has of value!

I agree. And containers can become petrie dishes for all sorts of bad stuff. -- Susan

i have discovered the blight in my tomatoes. is there anything i can do to the unafected tomatoes so i can still use them. wash them with something to save them?

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About Susan Reimer
Susan Reimer has spent 16 years writing about raising kids - among other topics - in her column for The Baltimore Sun. And every time son Joseph or daughter Jessie passed another milestone - driver's license, college, wedding or a move to a new military duty station - she has planted another garden. Now she will be writing about those gardens - and yours - here on Garden Variety.

Susan isn't an expert gardener, but she wasn't an expert mother, either. Both - the kids and the gardens - seem to be doing well in spite of her.

She lives in Annapolis with her husband, Gary Mihoces, who loves to cut his grass but has noticed that there seems to be less of it every time the kids pass another milestone.

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