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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis

Broadleaf Weed Control

Posted by John Fulton -

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. We have also been waiting for a period of drier conditions with lighter winds. 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 (mecoprop), dicamba, a combination of those three products, and triclopyr alone or in combination. 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 under active ingredients.

2,4-D is the old standby. 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 with hot and humid conditions. There are amine, low volatile ester, and ester formulations of many of these products. The amines are water soluble and don't vapor drift as much. The ester forms are much more likely to vapor drift, but also penetrate weed leaves better.

Weeds can also be an indicator of turf condition. Around here, crabgrass and white clover may be an indicator your mowing height is too low. Most cool season grasses should be mowed at a minimum of two inches tall. If you have an abundance of these weeds, try mowing a half inch higher. Of course, these same weeds tend to fill in spaces where turf grasses are absent.

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