To understand the basics of weed control one should familiarize themselves with the basic terms below. If you are already familiar with terms you can jump to... Pre-emergence in lawns, Post-emergence in lawns, Bare ground weed control, Bare ground weed control when weeds are present and Zone treatments for yards with a little of everything.
Pre-emergence -An application to prevent weeds from germinating.
Germination - When a SEED opens to form a new plant.
Post-emergence - An application made to kill existing weeds.
Annual weeds -Weeds that germinate and die in one cycle, typically 2 or 3 seasons. Summer annuals germinate in the spring or summer and die that fall or winter. Winter annuals germinate in fall or winter and die in spring or summer. Example: Russian Thistle (Tumbleweeds)
Biennial Weeds -Weeds that take two years to mature and die. They act like annuals the first year except they don’t produce seeds; they die back in the winter and re-grow from rootstock to come back the second year. During their second year they produce seeds before dying. They do not come back a third year from rootstock. By the third year of introduction of biennial weeds you will find them in both stages. Example: Silverleaf Nightshade
Perennial Weeds -Weeds that produce seeds like annuals but return from rootstock or rhizomes as well. Example: Dandelions, African rue
Rhizomes - Roots that run laterally from the main plant and produce new plants from nodes. Example: Bermuda Grass
Root Active - An herbicide that kills weeds by absorbing the material through its roots. These materials work like regular Pre-emergent materials but also can damage desirable plants.
Grass weeds - A weed that has long slender leaves with veins that run parallel from the base. Grasses are monocots. Examples: Bermuda Grass, Foxtail, Sandbur.
Monocot - Plants that form one leaf after germination.
Broadleaf weeds - Weeds that have leaves with veins radiating from the base (palmate venation) and are dicot.
Dicot - Plants that form two leaves at germination.
Residual - A material that is effective for some period of time.
Pre-emergence in lawns is guaranteed to prevent seeds from germinating for 90 days. This is an excellent way to prevent new summer and winter annuals and to prevent the spread of biennial and perennial weeds by seed germination. This needs to be repeated every quarter as weed seeds are constantly introduced to the lawn by wind, birds and other animals. Constant watering also reduces longevity of material. These materials are residual for about 3 months in lawns.
Post-emergence in lawns is often done with a backpack sprayer and is targeted directly to areas with broadleaf weeds. This is called spot treating. In some cases a power spray is done and can be tank mixed with pre-emergent materials. Because post-emergent materials can affect desirable plants such as flowers and shrubs, this will prohibit treatment immediately next to desirables. Weeds near desirable should be pulled or spot sprayed with a smaller sprayer. When pre and post emergent materials are mixed, the pre-emergent material doesn’t get near desirables so weeds can become worse there. We recommend that post-emergent powerspray treatments be done on the first visit to get quicker control when weeds are thick and actively growing. We recommend that you assist in the weed program through weekly spot treatments. This has proven to be the most effective program. Post-emergent materials in lawns normally have no residual properties.
Bare ground weed control can be provided in and around desirable plants or to large open areas. It is most effective when applied to bare ground, as these materials must get into the soil. Rain or irrigation is required to get materials out of the sun and into the soil. They work just like the pre-emergent materials mentioned above. In some cases root active materials may be applied. These materials are residual for 6 months to a year or longer.
Bare ground weed control when weeds are present has some unique problems depending on the size or density of the weeds. As stated above to work properly, pre-emergent materials have to reach the ground so if you can’t see the ground through the weeds, they’re probably too dense. Some weeds may be only an inch or two in height but are very dense and spread out over a large area. If irrigation or rainfall occurs immediately after application the materials may be washed through the weeds to the ground, but we strongly recommend removing the weeds first. Besides, dead weeds can be just as unsightly. One advantage to treating the existing weeds first of course is that dead weeds can be considerable easier to remove. A repeat application may be needed, if this is done, as the pre-emergent materials may not reach the soil. Also, with post-emergent materials there is a slight risk of damage to nearby desirable plants.
We can apply post-emergent materials only to existing weeds to kill them. You may choose to mow them to a more desirable height before the treatment. In this case a week should pass after mowing to allow weeds to return to a state in which they are more susceptible to herbicides.
Zone treatments are often performed on the same property using two or more different materials. One that is safe around desirable plants and others in open areas. Longer residuals can be obtained in areas where desirable plants are not a concern.