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The Blight is Everywhere

Sun, Aug 20th, 2000
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Monday, August 21, 2000

Can we talk enough about Tomato Blight? I dont think so. Up until last week I was so full of myself. Oh no, I had added compost and mulched and done all the right things, you all had blight, but not me. But I have been humbled. The Blight is everywhere, (except for one of my neighbors who has no blight, but he has no fruit yet either.) So without being redundant here is everything you ever wanted to know about blight, but were afraid to ask.

What is Tomato Blight?
Firstly, there is Early Blight and there is Late Blight. Early Blight is characterized by concentric rings of dark brown or black leaf spots that form a target. Leaves will go brown and wither. This disease usually shows up mid- to late- summer.

Late Blight shows up when the nights are cool and the days are warm and things are really wet. Plants look like they have frost damage. It usually comes on fast. In a matter of a few days the leaves will look water-soaked and may have a white downy fungus growth on the underside of the leaves. Fruit may also be injured and may have large, wrinkly, discolored dark spots that look like the tomatoes were frozen.

Both are fungal diseases that can be soil borne or wind-borne. But there is more. Another common disease of tomato is Septoria Leaf Spot. This is also a fungal disease and is very similar to Early Blight. Septoria Leaf Spot usually doesnt show up until after fruit set but Early Blight can show up anytime. And like Early Blight it can defoliate an entire plant. Now to look at a tomato plant and see the leaves covered in dark spots, going yellow then brown and always working its way from the lowest leaves upward you could have either the Early Blight or Septoria Leaf Spot. To tell the difference you have to look closely at the spots themselves. The spots of Early Blight as we mentioned have a target pattern, they form rings of dried tissue and can show up anytime. The spots formed by Septoria Leaf Spot are smaller, more numerous and usually have white or grey centers.

So what can you do? Fellow M.G. Opal Schrock recommends total removal of all infected plants and I agree. Anytime you are dealing with a fungal disease every little spot is a spore-producing factory spreading more and more fungus. Once you have signs of blight there isnt a lot you can do.

As you plan your garden for next year dont plant tomatoes or other nightshade family members including potatoes or eggplant in the same place more than once every 4 years. Avoid overhead watering. Trellising or staking tomatoes helps to keep foliage up off the ground and keep air flowing around the plants to keep leaves dry. Always keep at least two feet between plants for best air circulation.

Once you have blight or leaf spot fungus in your garden those spores will be around for a long time. As a preventative you can use Copper or Bordeaux mixture. These fungicides are considered organic and should be used following manufacturers recommendations. Next year give your tomatoes all the extra help they need with good doses of compost or well-rotted manure. Tomatoes are a native to South America and they like a rich warm soil. If you put your plants out earlier than last frost dates use soil warmers like black plastic, row covers or the new "wall o water" to hold in heat.

Virginia Cooper gardens and battles tomato blight from her farm in Mabel. She can be reached at the Extension office at (507) 765-3896, or via email:

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