Begin killing summer weeds now during the dormant season

By By Steve Strong / area horticulture extension agent
Feb. 4, 2004
Many gardeners do not think about weed control in home lawns and flowerbeds until the weeds have already become established.
By the time the weeds produce a mature root system, it is usually too late for effective control with herbicides, and such is the case with winter annuals like henbit and wild garlic that have been present in landscapes since the start of the cool season.
While little can be done now for these established winter weeds besides mowing them, mid-February through early March offers the best time to control spring and summer annual weeds that will soon be sprouting.
Weeds are much easier to wipe out during the seedling stage by using some type of pre-emergent weed killer, and several herbicides are available for managing both grassy and broadleaf problems.
Trifluralin is sold under a number of brand names including Treflan, Preen, and Trilin, and is most effective in managing spring grassy weeds. This herbicide may be used in places like daylily beds, shrubbery and even vegetable gardens to control crabgrass and other monocots (grassy plants), while causing no harm to broadleaf plants in the same area.
Be aware that a grass-killing herbicide does not distinguish between a grassy weed and your lawn turf, and it may have the same deadly effect if accidentally applied to your St. Augustine. Make sure to read the label carefully before applying any herbicide, checking for label rates and for lists of plants that may be sensitive to certain weed killers.
The broadleaf herbicide of choice for homeowners is isoxaben, and is sold under the brand names Gallery and Portrait. Isoxaben is great for controlling dandelions and a multitude of other broadleaf weeds, and is labeled for both lawn turf and landscaped beds. Isoxaben and trifluralin are also sold in a pre-mix combination called Snapshot, offering a one-two punch for pre-emergent weed control.
The keys to controlling noxious weeds without harming your prized plants are timing (dormant season is best before soil temperatures reach the mid-40s), rate of application (follow the label) and uniform coverage. A crisscross pattern should be used to apply granular herbicides in the same way as a fertilizer application, and colored dyes can be added to spray mixes to mark where they fall.
The herbicide label will provide a list of weed species that the active ingredient will control and at what rate. If several weed species are being targeted, use a rate that controls the most difficult weed. When making herbicide applications on lawn turf, be sure to stay well within the rates listed for your turf species (St. Augustine is the most sensitive of the southern turf grasses).
Pre-emergent herbicides create a thin weed control barrier on the soil surface, and uniform coverage is essential to prevent any weed seedling escapes. Liquid or granular herbicide applications should be carefully calibrated or measured on a small area first to ensure a uniform weed control barrier is applied.
Finally, herbicides must be activated once they are applied, and activation usually requires about a half-inch of rainfall or irrigation shortly after application. Water helps to move the product down through the turf leaf canopy or bed mulch layer so that the weed barrier can become established at the soil surface.
Many additional herbicides are available for home landscape use besides those mentioned previously, and the weed control options listed are simply provided as a starting point. Check with the MSU Extension Web site at www.msucares.com for more detailed information on controlling weeds in home lawns or gardens, or contact your local county Extension office.
Until next time, remember a weed is only a weed when it pops up in a place where it is not wanted. Think about that this month as the lovely yellow Carolina Jessamine begins to bloom.