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Start your battle against weeds now

October 5, 2012 12:10 am

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If you're trying to keep your lawn weed-free, flowering chickweed is not something you want to see.

FALL IS A good time to control broadleaf weeds that could spring up in late winter and early next spring. Many of these broadleaf weeds, called winter annual weeds, germinate in the late summer and fall.

They could then grow during any stretch of warm weather, even in the middle of the winter. Otherwise they'll remain dormant until spring when they normally resume growth, produce seed, and then die as temperatures increase in late spring and early summer.

Common winter annual weeds in this area are common chickweed, henbit, purple deadnettle, corn speedwell and buttercups, among others.

Many perennial weeds can be controlled in the fall too. Fall is when perennial weeds are moving energy reserves to the roots in preparation for winter dormancy and herbicide can move right along with the energy reserves. Some common perennial weeds are ground ivy or creeping Charlie, white clover, mouse-ear chickweed and dandelion.

Perennial weeds are more difficult to control, as they can grow from roots, rhizomes or seed and may require fall and spring herbicide applications.

These broadleaf weeds are best controlled by a post emergent, meaning post-germination, herbicide. The timing of the herbicide application is a key part of gaining a good level of control. The weeds need to be actively growing, which occurs when there is good moisture and the daytime air temperature reaches 70 degrees.

Most of the herbicides available are effective when the daytime temperature is 50 degrees or better. The weeds need to be actively growing to allow the herbicide to be taken in and spread throughout the plant. Additionally, this will allow time for the grass to fill in voids left after the weeds are killed.

October and early November provide very good control opportunities for broadleaf weed control in the Fredericksburg area.

Herbicides applied as a spray to foliage and not washed off by rain provide very effective broadleaf weed control. Granular formulations are available but the granular products must be applied to moist (dew-covered) foliage for optimum control.

Herbicide applications on lawns that have been over seeded this fall should be delayed until the new grass has been mowed twice. This delay is necessary because new grass seedlings are sensitive to the herbicides.

Broadleaf weeds can be controlled by a number of herbicides available to homeowners. Look for products that contain combination of two or more of these active ingredients: 2,4-D, 2,4-DP, dicamba, MCPP, MCPA, quinclorac, triclopyr, carfentrazone, sulfentrazone, and penoxsulam. (Penoxsulam is found in granular products only.)

There are well over 100 consumer broadleaf herbicide products registered in Virginia. Just use the active ingredients list when shopping. Read the herbicide label carefully to ensure a particular product is safe and to determine the timing between seeding and application of the product.

Herbicides are only part of the weed control answer. Maintaining a healthy lawn is also key. Good healthy lawns will naturally control more weeds than we can combat with chemicals.

To foster healthy turf:

Maintain a soil pH of 6.2 to 6.8, with lime applications based on soil test results.

For cool season lawns follow a fall fertilization schedule to encourage root development. Applying two applications of 1 pound of nitrogen per 1,000 square feet is adequate for residential turf. Recycle clippings when you mow as this recycles nutrients and does not contribute to thatch buildup.

Mow your lawn frequently enough so you remove less than of the leaf. The proper height for mowing fescue, our most common cool season grass, is 2 to 3 inches.





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