One of the first steps in the seasonal battle against weeds is learning how to identify the common types found in this part of Texas. Proper identification will help you choose a herbicide that effectively targets the weeds in your lawn.
Identifying Weeds
There are three types of weeds found in lawns:
1. Broadleaf weeds:
- They emerge from the soil with two leaves
- Their leaves are wide with a main center vein that branches out into smaller ones
- Some have single flowers, while others grow clusters of blossoms
- Roots vary — large, single taproot, a system of thin roots, or a combination of both
- They grow upright or close to the ground
- The stems can be round or square
- Examples: carpetweed, spotted spurge, dandelions, purslane, henbit, common chickweed, clover, and thistle.
2. Grassy weeds:
- Closely resemble lawn grass, making them difficult to identify
- They emerge from the soil as a single leaf
- The stems are round and hollow, with alternating leaf blades on each side. There are visible bulges or joints where the leaves attach (nodes)
- Leaf blades have long, parallel veins
- Usually no showy flowers
- Grow mostly in clumps
- Examples: crabgrass, dallisgrass, sandbur, johnsongrass, and quackgrass
3. Sedges:
- Hard to distinguish from grass
- Stems are usually solid and triangular, with three leaves per stem
- Leaf blades appear waxy, and have a v-shaped groove
- Seedheads look different on each type of grassy weed, but rarely appear in frequently-mowed grass
- Examples: yellow nutsedge, purple nutsedge, annual sedge, and green kyllinga
Weed Life Cycles
Knowing how your weed type grows and reproduces will also help in selecting herbicides and scheduling applications. There are three different weed life cycles:
1. Annual: Annual weeds germinate from seed, mature, and die within twelve months. With a few exceptions, most only live for about half a year. Before dying, annuals drop seeds that emerge the following year to start a new cycle.
Summer annuals sprout in the spring or early summer, and die in the fall with the first killing frost. Winter annuals germinate in the fall or early winter, and die in late spring or early summer as the soil and air temperatures heat up.
Summer annual examples: crabgrass, sandbur, spotted spurge, carpetweed, and annual sedge.
Winter annual examples: annual bluegrass, common chickweed, and henbit.
2. Biennial: Biennial plants live for two years. Seeds germinate in the spring, summer, or fall of the first year without flowering, and overwinter as a rosette (radial cluster of leaves close to the soil surface). In the summer of the second year, biennial weeds send up a stalk, flower, and set seeds before dying in the fall.
Biennial weed examples: common mullein, musk thistle, and wild carrot (Queen Anne’s lace).
3. Perennial: Perennial weeds live for three or more years. They spread by seeds, stolons (horizontal stems above ground), or rhizomes (horizontal stems below ground).
Simple perennials spread only by seeds, and have taproots that can grow quite large. Spreading or creeping perennials begin life as a seed, but then reproduce vegetatively from stolons or rhizomes.
All perennials can store food underground over the winter, which allows them to reappear in the spring. They are the most difficult weeds to control.
Perennial examples: yellow and purple nutsedge, dallisgrass, quackgrass and dandelion.
Turfgrass Types
St. Augustine, Bermuda (common or hybrid), zoysia (coarse or fine), and buffalo are common warm-grass types in central Texas.
It’s important to know your type of turfgrass and cultivar (improved varieties of grass created and maintained by cultivation) in order to protect it when treating weeds. St. Augustine Floratam, and Emerald zoysia are examples of cultivars. Herbicide labels often provide information specific to cultivars, such as prohibiting application, or specifying lower application rates.
Weed Control
Weed control begins with proper lawn management practices such as:
- Irrigating and fertilizing
- Dethatching and aerating
- Mowing regularly at the correct height for grass type
- Bagging and removing grass clippings when weeds are producing flowers and seed heads
- Hand-pulling and using hand tools to remove weeds
- Controlling diseases and insects
Herbicides
You may need to apply herbicides if weeds reach an unacceptable level, and there are too many to remove manually or by using hand tools. Different weed life stages require either a pre-emergent or post-emergent herbicide.
Pre-emergents are applied before the weed starts to germinate, and are most effective with annuals. They form a thin, invisible barrier on the soil that blocks seeds from sprouting.
Pre-emergents should be applied three times a year to kill spring, summer and fall/winter weeds. They should only be used on established grass because they also prevent new plants and grass seed from sprouting.
When is the Best Time to Apply Pre-Emergents?
- Spring when the temperature is over 55°F for 2-3 consecutive days, from late February to early March
- Second application about 3 months after the first, to prevent summer annuals
- Third application in the fall, usually September, when soil temperatures drop below 70°F for 2-3 consecutive days
For determining soil temperature, homeowners can use soil temperature probes, probe-type meat thermometers, or soil temperature maps.
Post-emergents are applied after the weeds are visible in your lawn. They control annuals, biennials, and perennials, and work best in the late spring for summer annuals when the weeds are still small and in their growth stage.
If the weeds have matured, they may require several applications during the summer. Post-emergents can also be applied in the fall when weeds are preparing for winter. Both pre- and post-emergents can be used at the same time, especially if you’re splitting the pre-emergent over a couple of months.
Post-emergent herbicides are also classified into selective and non-selective. Selective herbicides target certain weeds without damaging the surrounding grass. Non-selective usually kill any plants they contact, including grass.
There are two options for controlling weeds using post-emergents:
Systemic Herbicides
- Prevent the weed from growing again by destroying the weed and the root.
- Take longer to kill weeds
- Most are selective
Contact Herbicides
- Destroy parts of the weed they touch, such as the leaves and stem, preventing photosynthesis
- Work faster than systemic post-emergents
- Often have to be reapplied when weeds grow back
Some herbicides combine both systemic and contact chemicals for a faster effect.
Call the experts at South Austin Irrigation at (512) 534-7449 or fill out our Service Request form for professional maintenance and repair to your sprinkler system.
