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Broadleaf weed control and cedar apple rust

By John Fulton

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[April 28, 2008]  Everyone seems to have been waiting for warmer temperatures and the appointed date to begin broadleaf weed control programs. Well, that time will come, believe it or not. For most of the broadleaf products to work, the temperature has to be over 55 degrees. These chemicals do work better when it is warmer and the weeds are actively growing. 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 hard-to-control weeds and woody plants. It also improves control of violets. It can be added to one or more other chemicals to provide broad-spectrum control. Some blends now contain trichlopyr, so check the label.

The old standby is 2,4-D. It is good on carpetweed, chicory, dandelion, lambsquarters, plantains and wild carrot. MCPP is good on chicory, lambsquarters and white clover. Dicamba is good on black medic, chickweeds, chicory, dandelion, dock, henbit, knotweed, lambsquarters, 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 products can drift as a vapor for up to two weeks after spraying in hot and humid conditions.

Cedar apple rust

Cedar apple rust is caused by a fungus that attacks two different groups of trees. The first group is apples and crab apples, and the second is juniper and eastern red cedar. In order to survive, the fungus must "move" from one group of host to the other.

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On juniper, or eastern red cedar, small (three-eighths to 1 3/16 inches in diameter) galls develop throughout the tree on needles and small twigs. When mature, these galls swell considerably and repeatedly produce orange, jello-like horns during rainy spring weather. As spring rains subside, the galls die, which may cause death of the twig from the gall to the tip.

On susceptible crab apples and apples, tiny yellow spots appear on the leaves after infection in the spring. As the spots mature, they become yellow-orange and swollen, with a red border, and develop tiny black dots in the center of the lesion. By midsummer, small cup-like structures with tubes are visible on the undersides of mature leaf lesions. The fungus may also infect fruit and tender twigs of very susceptible crab apple and apple varieties.

The entire life cycle takes about two years, with a year on each host. The apple phase is easily recognized on the leaves and fruit by just about anybody who has grown apples. The teliospore phase on the cedars is quite striking but is noticed much less frequently.

Fungicides in spray programs do a good job of controlling the apple phase, while the cedar phase is best controlled by buying resistant varieties. Some homeowners cut the galls off before they break out into the "orange blob," but the result is the same: You're going to likely lose the tips on those branches.

[By JOHN FULTON, University of Illinois Extension, Logan County]

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