Different weeds take distinct measures to control them

Published: Wednesday, Oct. 12 2011 10:18 a.m. MDT

Dandelions are a perennial weed with a large taproot. Dig them out or spray them in the fall. (Larry Sagers,) Dandelions are a perennial weed with a large taproot. Dig them out or spray them in the fall. (Larry Sagers,)

RLast week's column covered what makes a plant a weed and one way that weeds are classified. This week the focus is on specific kinds of weeds and how to best control them.

I classify weeds into five convenient groups to determine their control method. These are annual grasses, perennial grasses, annual broadleaves and perennial broadleaves, including plants with woody stems.

Weeds have specific times in their life cycles when they are the easiest to control. The stages are seed, seedling, vegetative growth, flowering, seed formation and finally death of the plant.

Determine the plant growth stage when they are most susceptible. It is almost impossible to control seeds once the plant forms them. Dormant seeds are highly resistant to most controls. By contrast, the germinated seedlings are very vulnerable. They are shallow rooted and even perennial plants need 30 days of growth before they become perennial.

Broadleaf weedkillers, such as these products, kill the weeds in lawn areas. (Larry Sagers,) Broadleaf weedkillers, such as these products, kill the weeds in lawn areas. (Larry Sagers,)

Seedling control is the preferred option. It controls annuals and perennials and grasses and broadleaves. Hoeing, tilling and other cultivation methods offer excellent control.

Another option is a pre-emergent herbicide. These products do not kill seeds but they form a barrier that kills the weed's seedling after it emerges. Some products work best on grasses while others are more effective on broadleaf weeds.

They are often sold as "weed preventers" or "crabgrass preventers." These products do not control established weeds. Read and follow all label directions to protect pets, plants and people.

Annual weeds are easier to control because they have shallow root systems and nature kills them off for you each season. They are problems because they are among the most prolific seed producers. Remove them before they drop their seeds to reduce the seeds for future years.

Field bindweed           (Larry Sagers,) Field bindweed (Larry Sagers,)

Biennial plants typically grow a rosette or a vegetative stage the first year and produce flowers and seed the second season. While the seedling stage is the most susceptible, the next best time to control biennials is in the fall of their first year of growth.

Many biennials have large taproots they use as storage organs to get the energy to grow next year. Digging or spot spraying right now is an effective control for most biennial weeds.

The most difficult weeds to control are the perennials. Finding the right way to control these depends on what type of weed you are battling. Simple perennials have a root system that does not spread. Examples are common mallow and dandelion.

Creeping perennials spread by stolons, rhizomes or tubers. Bentgrass spreads by above-ground stolons, quackgrass spreads by underground rhizomes and Bermudagrass spreads by both. Canada thistle, field bindweed or wild morning glory are in this group. Yellow nutsedge produces small tubers and other weeds produce bulbs or other vegetative propagules.

Products containing glyposate are nonselective but do not move through the soil. (Larry Sagers,) Products containing glyposate are nonselective but do not move through the soil. (Larry Sagers,)

Because these weeds propagate vegetatively, cultivation is not effective because tilling the plant cuts the stolons or rhizomes into sections. Each section can grow into new plants.

Fall is the best time to spray these plants because the plant will move the herbicide to the root system. Until you kill the roots and rhizomes, you cannot get any effective control.

Now that temperatures are dropping, it is time to spray them. Applying the herbicides now means they will absorb into the leaves and translocate to the roots. If you can kill the roots, you can get these weeds under control.

In the lawn areas use a selective product containing a broadleaf weed killer. These are available under many brand names from local nurseries. They will control the broadleaf weeds while not damaging the grasses.

Thistles in the rosette stage. These are biennials. (Larry Sagers,) Thistles in the rosette stage. These are biennials. (Larry Sagers,)

For areas where you have no desirable plants or where you have sensitive plants that are likely to be affected by the broadleaf weed killers, switch to glyphosate or Roundup. Glyphosate is the active ingredient but is sold under many trade names.

These are nonselective herbicides so never get it onto anything but the weeds. One important advantage is that it does not go through the soil and affect surrounding plants.

Apply herbicides while you still have good green foliage that has not dried out or frozen. Dead foliage will not absorb the product and translocate to the root system so you would get no control. Time spent controlling weeds now will make your life easier next spring.

Larry A. Sagers is a horticulture specialist for the Utah State University Extension Service at Thanksgiving Point.

Garden Tips

Red Butte Gardens Bulb Forcing Workshop, October 15, 10 a.m.-noon. Brighten the winter blues by planting spring bulbs for winter forcing. Participants will get four 6-inch pots, soil, selected bulbs and instructions for forcing. Workshop is at Red Butte Garden greenhouses. Members: $45, Public: $55 register at www.red buttegarden.org/

Apples Galore is a free apple and cheese tasting event for gardeners. Come satisfy taste buds and sample Utah's finest artisan cheeses and locally grown apples — the perfect combination for a perfect end to the season. Oct. 13, noon-2 p.m. at the Ogden Botanical Gardens, 1750 Monroe Blvd., Ogden, and that evening 5 p.m.-7 p.m. at the Utah Botanical Center at 920 S. 50 West, Kaysville. See utahbotanicalcenter.org.

Thanksgiving Point is offering a class on fabulous fall color on Tuesdays, Oct. 11-25, 10 a.m. to 12:30 p.m. Cost is $40. To register, or for more information, call 801-768-7443 or visit www.thanksgivingpoint.com.

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