Weed control is a year-round activity, and the end of winter to late spring is one of the key times to apply a herbicide to your lawn. Usually in the Austin and San Antonio areas this occurs between February 19th and March 5th when the temperatures remain around 55°F for 4 or 5 consecutive days. However, this year is different due to the extended period of winter frigid temperatures that damaged many of our warm-season turfgrasses.
As a result, you may have seen a delayed recovery and green up of your lawn. Texas A&M specialists recommend that you hold off using any herbicides until a full green-up has occurred. This will allow you to assess for damage and reseed or resod any areas where the grass is thinner or has died.
After your lawn has greened up, and any reseeding or resodding is completed, here are some helpful steps to help you choose the right herbicides:
Know Your Weeds
1. Start by identifying the general types of weeds in your lawn. There are three types:
- Broadleaf: emerges as seedlings with two leaves. Leaves are broad and have netlike veins. Many have showy flowers. Examples include carpetweed, spotted spurge, dandelions, and purslane.
- Grassy: hard to identify because they often resemble grass. Blades have a single leaf with long, parallel veins. The round stems have alternating leaf blades on each side. Usually there are no showy flowers. Most grow in clumps instead of spreading evenly on the lawn. Examples include crabgrass, dallisgrass, sandbur, and johnsongrass.
- Sedges: usually have solid, triangular stems, with three leaves per stem. Examples include yellow nutsedge, purple nutsedge, and green kyllinga.
2. Learn the life cycle of the weeds in your lawn — how they grow and reproduce. This will help you with herbicide selection and application timing. The different life cycles are:
- Annual: annual weeds germinate from seed and live for just one growing season. When they drop seeds before dying, new annuals will pop up the next year. Summer annuals usually sprout in the spring or early summer and die back in the fall. Winter annuals sprout normally in the fall or early winter and die back in the late spring or early summer. Examples: crabgrass, carpetweed, and annual sedge.
- Biennial: biennial weeds normally live for two years. In the first year, seeds sprout and grow without flowering, forming a rosette (radial cluster of leaves close to the ground). During the second year, they develop a stalk, flower, set seeds, and die. New biennial weeds can grow the next year from the seeds. Examples: common mullein, musk thistle, and wild carrot (Queen Anne’s lace).
- Perennial: perennial plants don’t die after flowering and live for many years. All perennials have underground structures for storing food over the winter so they can reemerge in the spring. These are the most difficult weeds to control. Yellow and purple nutsedge, dallisgrass, and dandelion are perennials.
Know Your Turfgrass Type
Common warm-season turfgrasses in central Texas include: Bermuda (common or hybrid), zoysia (coarse or fine), St. Augustine, and buffalo.
Choosing a Herbicide
Herbicides are classified as pre-emergent or post-emergent, depending on a weed’s stage of development. Pre-emergents prevent the development and emergence of weeds and are most effective on annuals. Post-emergents kill weeds after they appear in your lawn, and can be used to control annuals, biennials, and perennials. They work best in the late spring when the weeds are small and actively growing. It may take several applications in the summer to fully control mature weeds.
Because of a possible delay in your lawn’s green up this year, you may have missed the window (February 19-March 5th) for applying a pre-emergent. However, if you didn’t do any reseeding or resodding you can use a post-emergent for growing weeds.
As well, between May 22nd and June 5th, you can apply a summer pre-emergent to catch different weed species that may now be sprouting. Alternatively, you may want to use a pre- and post-emergent combined product to attack weeds in both stages.
Both newly sprouted grass and fresh sod need time to establish root growth before you apply herbicides. For pre-emergents, wait at least 4 months before using on new grass, and for sod wait between 3-6 months (in time for a fall pre-emergent). To apply post-emergents, wait until new grass and sod have been mowed 3 times. It’s actually best not to apply any herbicides during the first year after seeding or sodding.
Always follow the herbicide label instructions for application rates, timing, and appropriate turfgrass species. Some herbicides are targeted for specific weeds (selective herbicides), while others will kill all vegetation (non-selective), including the turfgrass.
Systemic vs. Contact Post-Emergents
Systemic post-emergent herbicides destroy both the weed and the root, preventing the weed from growing again. It can take up to a week to see results. Most selective herbicides are systemic.
Contact post-emergents damage only the parts of the weed they come into contact with. For example, if the leaves are targeted the weed can no longer photosynthesize and won’t receive nourishment. These herbicides work faster than systemic post-emergents, but since the roots may not be destroyed, the weed may reappear again.
Granular or Liquid
Herbicides can be liquid or granular. The granular ones are small pellets coated with herbicide, and are applied through a spreader (handheld, rotary, or drop spreader). Most granular products should be applied when the temperature is between 65 and 85°F to avoid turf damage. They need to be watered in to release the active ingredients in the granules. Use a sprinkler, or irrigation system to wet down the lawn. You can also use rainfall if it’s within three days of application.
Liquid products may need to be mixed with water. Use a sprayer to either spot treat or blanket your whole lawn. Also apply liquid herbicides when the temperature is below 85°F to protect the turf.
Organic Weed Control
Organic weed killers are made completely from naturally-occurring chemicals, and fall under the category of contact herbicides. They are also non-selective, so they must be carefully applied.
There are only a few organic herbicide ingredients. One of the most popular is corn gluten meal, which is used as a pre-emergent on turfgrass. Others are post-emergents, and are used as ingredients in the relatively few commercial organic herbicides:
- Herbicidal soaps with long-chain fatty acids.
- Citric acid.
- Vinegar or acidic acid in high concentration (not regular household vinegar).
- D-limonene, found in citrus peels such as grapefruit, mandarin, orange, lime, and lemon.
- Essential oils, such as cinnamon, clove, red thyme, and summary savory.
Organic herbicides are the most effective on younger, smaller weeds, and in temperatures above 75°F in full sunlight. For best results, use them along with other weed control methods.
Additional Weed Management
In addition to using herbicides, do the following:
- Mow your lawn regularly to the correct height for its type. Bag and remove clippings when weeds are producing flowers and seed heads.
- Hand-pull and use hand tools to get rid of weeds (e.g. a hoe type that moves horizontally underneath the soil and doesn’t bring seeds to the surface). Manual removal can be more effective than post-emergent herbicides with mature weeds.
- Irrigate and fertilize properly to maintain a healthy, dense lawn that can better resist weeds.
One of the best ways to maintain a lush, healthy lawn is with a professionally maintained sprinkler system. Call the experts at South Austin Irrigation at (512) 534-7449 or fill out our online Service Request form for your sprinkler system maintenance and repair needs.