Garden Guide

Understanding weed control
Mar. 13, 2013 @ 05:00 AM

What is a weed? A weed is simply a plant out of place. There are many common weeds that can sprout up in lawns, flower beds, vegetable gardens and driveways. Judging from the calls, weeds often get out of control in Lee County.   

Weeds, like other plants, may be annual, biennial, or perennial. Annual weeds complete their entire life cycle (germination, growth, flower and seed) in one year. Biennial plants grow clustered leaves the first year and, in the second year, produce flowers and seed. Perennial plants live for many years and often produce seeds each year.

The annual life cycle is broken down into when the plant typically grows. Winter annual weeds germinate in the fall or early spring and flower and die in spring or summer. Common examples of winter annuals are henbit, lawn burweed, annual bluegrass and chickweed. Summer annuals germinate in spring and summer then flower and die in late summer or fall. Common examples of summer annual weeds include crabgrass and pigweed. It is important to know the weed’s life cycle in order to time and achieve the best control.   

That brings up another important point. It is absolutely critical to identify the weed. Know thy enemy. If you are having a hard time identifying the weed, bring a representative sample of the weed to our Center for positive identification. Also, when you drop off the plant, let us know where it is growing (centipedegrass, flower bed, vegetable garden, etc.) so that we can give you control solutions specific to that area.

One of the most effective (and long term!) weed control methods is to properly cultivate the area for what you are trying to grow. Give your turf, vegetables and flowers a fighting chance to out compete the weeds. Are you cutting your turf to the right height? Did you plant your cabbage during the right time? Have you taken a soil sample and amended the soil correctly? Are you trying to grow turf under a tree or in shade? Provide the best possible growing conditions to help your desired plants thrive!   

Mulch is another great weed defense. Organic mulches can be spread about 4 inches deep. Be careful if you are applying mulch near plants — you want to keep mulch about 4 inches away from the base of any plant to prevent rot. You can use bark, pine straw, newspapers, landscape fabric and others for mulch.

Mechanical methods, such as hand-pulling, hoeing and tillage, are always effective. However, their use in a landscape can be somewhat limited. In a vegetable garden, tillage and hoeing are especially important tools.   

Let’s talk briefly on herbicides — chemical products used for weed control. Keep in mind that no herbicide works on all weeds (again showing the need to identify the weed you want to control). There are many types of herbicides, below are some of the terms you may see:

Selective herbicides target certain plant species and will not seriously affect the growth of other non-related plants.   

Nonselective herbicides will affect and kill all green plants with no regard to species. These herbicides should be used with care and should not be applied over desired plants.

Contact herbicides only affect the portion of the plant that the spray came in contact with.   

Systemic herbicides are absorbed by the foliage and moved into the water and nutrient system. These herbicides will take longer to work than contact herbicides.

Preemergence herbicides are applied to an area before weed (or any other) seeds emerge. If you see the weed, it is too late to use a preemergence herbicide. For winter weeds, preemergence herbicides need to be applied by mid-September and again in November. For summer weeds, the preemergence should be applied in mid-February and again in mid-April. These herbicides need to be watered in.   

Postemergence herbicides are applied after the weed has emerged directly to the foliage. These herbicides require a rain-free period after application to be effective.

Herbicides are a combination of all the mentioned terms. For example, glyphosate is a nonselective, systemic, postemergent herbicide.   

Be careful when using weed-n-feed products that you are not applying fertilizer to your turf when it is not needed (especially with warm-season grasses).

The single most important step that you must take in weed control is identification of the weed. Promote healthy desired plant growth. Keep in mind that if you use chemicals without correcting soil conditions or using proper cultural methods, it will be a costly, yearly battle. When applying pesticides, the label is the law — read it and follow all instructions, including rate of application. For more information on weed identification or control, call our Center at (919) 775-5624.   

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North Carolina Cooperative Extension in Lee County.