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Leaf fungal diseases and broadleaf weed control          Send a link to a friend

By John Fulton

[MAY 2, 2006]  Reminiscent of the old song lyric "You call it potato...," it doesn't matter what you call it, but there are definite early signs of leaf problems beginning on shade trees. The major fungus that affects good-quality shade trees is anthracnose.

Anthracnose spots generally start along the leaf edges or between the veins. Eventually, the spots enlarge to become large blotches. Many of the affected leaves actually drop from the damage. Most often affected are sycamores, good-quality maples and other good-quality shade trees. In fact, anthracnose is one of those diseases that can affect everything from turf grass to tomatoes to trees.

With most fungi (that's plural for fungus), there are preventive applications available but no cure. The good news is that anthracnose on trees is usually a "limited damage" disease. Depending on the infection time, damage can include leaf loss, bud death or twig death. Large limb death means we have to look for another cause. In severe cases, anthracnose can make a tree lose all its leaves. For trees in good condition, a new set of leaves is usually out in less than six weeks.

Anthracnose can infect until nighttime temperatures reach and maintain about 65 degrees. This means we will probably have a while to feel the effects of the disease.

As for treatment, there isn't any direct, curative treatment available. You might have prevented it -- if you sprayed three or more times and had equipment that would spray the entire tree. The best thing to do is make sure all the small things are done. This includes watering when it is dry, fertilizing the tree at the lawn fertilizer rate and generally keeping the tree in good shape.

There are other fungal diseases that affect other types of trees. Apple scab gets production apples and crab apples; tar spot gets silver maples; etc. Fungal leaf spot diseases are all grouped together, with the same effects and recommendations.

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Broadleaf weed control

It is time to control your broadleaf weeds in the lawn in earnest. The first item of business is to know what type of weeds you want to control. This will make a big difference in what product or products you select.

The main products used for broadleaf weed control in lawns are 2,4-D, MCPP, dicamba, a combination of those three products and triclopyr.

Let's start with the triclopyr since it's probably the easiest to discuss. Its place in weed control is for violet control. It is death on violets. It can be added to one or more other chemicals to provide broad spectrum control. The locally available formulation from Ortho is Chickweed, Clover and Oxalis Killer.

The old standby is 2,4-D. It is good on carpetweed, chicory, dandelion, lamb's-quarters, plantains and wild carrot. MCPP (mecoprop) is good on chicory, lamb's-quarters and white clover. Dicamba is good on black medic, chickweeds, chicory, dandelion, dock, henbit, knotweed, lamb's-quarters, pearlwort, purslane, red sorrel, thistles, white clover, wild carrot and yarrow. The combination of all three products will pick up all of those listed for the individual products, plus a few more, such as mallow, speedwell and wild onion. The combinations are sold under many different trade names, so check the active ingredient list for ones you need.

My annual disclaimer for application of these types of products is: "Beware of potential drift from these products." Not only can the spray move under windy conditions while you are spraying, but particularly with dicamba, the product can drift as a vapor for up to two weeks after spraying in hot and humid conditions.

No brands are particularly endorsed. Brands named are as a convenience in finding products. The same active ingredients should be equally effective. Read and follow the label of any pesticide used.

[John Fulton, unit leader, University of Illinois Extension, Logan County Unit]

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