Weeds in turfgrass survive under adverse conditions

March 11, 2004
LORETTA JOHNSON and BRICE PAVLISH
Victoria County
Master Gardener Interns

You've got your grass going, and you discover these strange plants that are popping up everywhere. What is going on? Ah, weeds have infiltrated your lawn. No need to get out the flamethrower. You can deal with this, but it requires a bit of education.

Weeds are the most common pest problem in turf management. They compete aggressively for sunlight, moisture and nutrients. They seem to survive even under adverse conditions. Because of their variation in texture, growth, habit and color, weeds create an unsightly appearance in lawns. Proper turf grass maintenance is the best means of controlling weeds. In this article, which is the second of three on turfgrasses, we will deal with identifying weeds and controlling them. The third and last article will describe methods for maintaining healthy turfgrass.

Lawns damaged by improper care, insects, diseases, wear (compaction) or fundamental soil problems are highly susceptible to weed invasions. So, determine why the weeds established a foothold and correct those deficiencies. For instance, yellow nutsedge - commonly called nutgrass - and field sandbur - commonly called grass burs - are extremely resilient, and along with clover, which produces its own nitrogen, can thrive in poor soil.

An effective weed control program depends on the species of the weed and the type of turf that you have. Hand pulling is always an option that needs to be considered for control. Once weed population is out-of-hand, tilling or chemical control may be needed.

Turf weeds belong to three principal types - grassy weeds, broadleaf weeds and sedges (i.e., nutgrass). Weeds can be further grouped according to their life span - annual, perennial or biennial.

Annual weeds, such as grass burs and clover, germinate from seed each year, mature in one growing season and die in less than 12 months. Pre-emergent herbicides must be applied according to the expected date of emergence for each targeted species. Pre-emergent herbicides act to disrupt germination and growth of the weedy plant from seed. Consideration should be given to the overall condition of the lawn before application of a pre-emergent herbicide. Its use on a highly stressed lawn can increase damage to the turf grass. If the grass is brown, thin or not actively growing, the herbicide can increase damage. Always thoroughly water the lawn before and after application of a pre-emergent herbicide.

Perennial weeds, such as dichondra and yellow woodsorrel or oxalis, live more than one year and recover or regrow from dormant stolons, rhizomes or tubers as well as from seed. Control of perennial weeds requires a post-emergent herbicide during its season of active growth.

Besides weed classification and life span, season of active growth is also important to control. The warm-season grasses, such as crabgrass, goosegrass, sandbur and dallisgrass, are the major grassy weeds that cause problems in lawns during the summer, so weed control should be administered in the early spring. There are a few cool-season weedy grasses, such as rescuegrass, annual bluegrass and ryegrass, that can be controlled by pre-emergence herbicides applied in early fall, or by contact herbicides applied when the permanent turfgrass is dormant.

Only materials recommended for St. Augustine grass should be used on St. Augustine lawns, as the turf might be damaged by some materials that are safe for bermudagrass.

Always follow label directions for a product and observe all warnings relative to safety of the application. Products containing phenoxy herbicides (2,4-D) must be carefully handled to avoid wind drift and contamination of vegetable gardens or pet food and water. As with all pesticide use, triple rinse the sprayer after use and wash with ammonia before storing.

Remember, "the label is the law." Product labels will list the weeds for which the product ingredient is effective. Pay particular attention to cautions regarding use around trees. Remember that tree feeder roots can extend more than twice the diameter of the tree's above ground structure.

There are hundreds of weeds that may be giving you, the homeowner, problems. Obviously, it is beyond the scope of this article to describe even the most common weeds seen in the Victoria area. However, identification is not difficult with the help of some good references. Victoria County Extension Agent Joe Janak says that the most common weeds reported in area home turfgrass, classified by season, include: Cool season weeds - clover, thistle, annual bluegrass, chickkweed, dandelion, henbit and stinging nettle; Warm season weeds - annual Jewgrass, field sandbur, crabgrass, dallisgrass, bahiagrass, sprawling horseweed, dichrondra, pennywort (dollarweed) and bermudagrass.

Good Internet sites are:

http://aggie-turf.tamu.edu/pests.htm Go to "weeds" for an index of grassy, broadleaf and sedge weeds with drawings and description of each weed. Some of the more common weed descriptions also provide links to chemical control recommendations by Texas A&M.

Botanical terminology is explained in "Weed Identification, Using Plant Structures as a Key" at http://tcebookstore.org/tmppdfs/16061511-B6079.pdf

"Broadleaf Weed Control" for dandelion, chickweed, henbit, yellow sorrel, prostrate or spotted spurge, burweed, buttonweed and clovers at http://aggie-horticulture.tamu.edu/plantanswers/turf/publications/weed2.html

"Grassy Weed Control" for crabgrass, goosegrass, dallisgrass, bahiagrass and annual bluegrass at http://aggie-horticulture.tamu.edu/plantanswers/turf/publications/weed11.html

Those who want a paper copy of turfgrass weed control recommendations, stop by the county extension office, 528 Waco Circle at the Victoria Regional Airport.

So, in a nutshell, know your turf type, "name that weed," learn the proper control measure, and go to work. You will be amazed what a difference it will make to your lawn in health and appearance by taking some time now to whip it into shape.

Don't miss our final article on proper maintenance to keep turfgrass healthy and looking great, which is really the first step to preventing a weed problem.