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Features - Weed/Disease/Insect Control

How to manage those hard-to-control weeds.

February 22, 2011

We’ve all seen them. Yards with weeds running rampant, the turf choked.

The success of any lawn care company depends on the ability to prevent exactly that from happening.

“Generally, lack of effective weed control is the number one reason for customers cancelling their service,” says James McAfee, extension turfgrass specialist, Texas AgriLife Extension Service in Dallas. “It is important to be aware of the most common weeds found in the market, recognize the type of weeds (grass, broadleaf, sedge) and know the lifecycle of the different weeds (annual, biennial, perennial). Knowing the type of weed and knowing its lifecycle will allow the company to determine the best method of controlling the different weeds in their market.”

We spoke to experts about how and when to manage the hard-to-control weeds across the country. Use this color-coded guide to improve your work this season.
 

 

Crabgrass

The weed with the greatest stranglehold nationwide is crabgrass. The summer annual is light green in color and can be identified by its leaf blades, which can be longer than two inches, hairy and rolled in the bud.

Crabgrass germinates when soil temperatures reach about 55 degrees, which is important to note because it’s best controlled preemergently. Otherwise, it’s difficult to manage until fully mature.

“One of the things about crabgrass is it can be controlled by numerous different chemistries,” says Jim Goodrich, turf and ornamental product sales specialist, PBI/Gordon. “One of the more popular ones is quinclorac postemergent wise. Crabgrass tends to be hard to control because with that chemistry you need to get it when it’s mature or when it’s in its adolescence period, when it is producing seeds.”

Other recommended products are those that include the active ingredients: oxadiazon, pendimethalin, prodiamine and dithiopyr.

“We have actually started telling people that they can either tank mix or buy products that are already mixed together, but it’s basically a preemergence and postemergence herbicide that are combined together,” says Dave Gardner, associate professor in turfgrass science at The Ohio State University.


Dallisgrass

Dallisgrass is a warm-season perennial, coarse textured grassy weed that is light in color. The leaves are rolled in the bud, flat and wide. The weed mainly grows east to west from Virginia to California and the states south.

“This weed is found in most of the states in the Mid-Continent region and is especially a problem in the southern areas of the region such as Texas, Louisiana, Arkansas, Oklahoma and New Mexico,” says James McAfee, extension turfgrass specialist, Texas AgriLife Extension Service in Dallas. “The key to controlling dallisgrass is to prevent it from getting into the lawn in the first place. Producing a dense, healthy stand of turfgrass is one of the best methods for control of dallisgrass.”

Experts say preemergent herbicides containing dithiopyr can be used on the weed. The most effective control had been with arsenical herbicides like MSMA; however, the U.S. Environmental Protection Agency banned its use on commercial and residential lawns, making it hard to actually control and kill the weed.


Dollarweed

Dollarweed, which thrives in wet conditions, is a large problem in Florida and can be found in all Gulf Coast states. Also known as pennywort, its leaves are round in shape, about 1 inch in diameter and have scalloped edges. The leaves tend to be dark green and glossy.

“It does thrive in wet areas,” says Doug Obermann, turf and ornamental product manager, PBI/Gordon. “What happens in Florida is a lot of times irrigation is set for 20 minutes a cycle per zone. When it cools down in the winter and the days get shorter, there’s not as much transpiration or water being used, but people don’t change their watering cycle time intervals so they end up having wetter conditions than necessary.”

Obermann says spring is the best time of year to treat the weed and there is an abundance of products.

Both granular and liquid products can be used to kill the weed. Experts recommend products containing these combinations of active ingredients: 2,4-D, 2-ethylhexyl ester, mecoprop-p acid, dicamba acid and carfentrazone-ethyl; thiencarbazone-methyl, dicamba and iodosulfuron-methyl-sodium; penoxsulam.


Doveweed

Doveweed is found in southern states, such as Virginia, into Georgia and west to Texas. However Florida is most affected by the weed. Doveweed germinates later in the growing season and can be identified by short leaf sheaths with short hairs on the upper margins.

Doveweed is very difficult to control, says Patrick McCullough, extension turfgrass weed specialist, The University of Georgia.

“Repeat applications of the two- to three-way broadleaf herbicide mixture products have shown the best activity, but results are very inconsistent because doveweed can regrow after treatments,” McCullough says.

Why is doveweed so hard to control in lawns?

“It is a hard, woody weed,” says Patrick Bell, product manager, North America U.S. Turf and Ornamental Business, Dow AgroSciences. “You need repeat applications, and even then you’re not getting good enough control. The chemistry doesn’t exist right now where you’re able to control doveweed very well.”

What happens if you can’t control it?

“It will take over your lawn, whatever turf you have, to the point where you really would have to fall back on a glyphosate application, which is a total kill of the weed and the turf itself,” Bell says. “Then you would resod that area.”


English Daisy

For states in the Northeast region and along the Pacific Coast, English daisy causes problems because of its spreading habit. The leaves on the weed form a basal tuft or rosette, while its flower is comparable to daisies with white petals and yellow centers. The plant can be 3 to 4 inches tall.

“It can be hairy, which helps repel (herbicides),” says PBI/Gordon’s Obermann. “It is often very resistant to herbicides.”

The best time to treat English daisy is when it’s young and actively growing, meaning the spring. Obermann recommends products that contain the active ingredients: penoxsulam or triclopyr.
 

Ground Ivy

Also known as creeping charlie, ground ivy is found in the Northeast, Mid-Atlantic, Mid-Continent and North Central regions of the country.

The weed tends to grow in shaded areas and has leaves that are round to kidney shape and are opposite on petiole attached to stems that root at the nodes.

Ground ivy’s flowers come in  shades of blue to lavender. Its creeping growth is what makes it so difficult to control.

Ground ivy is generally controlled postemergently and can be treated in fall and mid-spring.

“We’ve had good success spraying creeping charlie in the fall, like in October,” says Ohio State’s Gardner.

Experts’ active ingredient recommendations include aptexor, fluroxypyr, triclopyr or dicamba. Specifically in warm season turfgrass, metsulfuron-methyl, will provide good control.

“A key to obtaining good ground ivy control is to get uniform coverage of the plant with the herbicide application,” says James McAfee, extension turfgrass specialist, Texas AgriLife Extension Service in Dallas.


Poa Annua

Also known as annual bluegrass, poa annua is a small clumped, yellow-green weed. The weed has boat-shaped tips and folds in at the bud. It can be found throughout the United States and tends to cause problems in the Southeast, Southwest and Northwest regions of the country.

Poa annua can be treated pre-emergently to prevent infestation and limit spreading. It tends to germinate in late summer and early fall when soil temperatures drop into the mid-70s.

“A second application can be applied in spring to control germinating plants,” says UGA’s McCullough.

“Fall applied preemergence herbicides cannot be used if reseeding or re-soding is needed to repair areas of damaged turf within several months after herbicide applications. Several preemergence herbicides effectively control annual bluegrass in fall and winter, which are similar to products used for summer annual weed control,” McCullough continues.

Among the products experts recommended: dithiopyr, oxadiazon, pendimethalin, prodiamine and indaziflam.


Nutsedge

There are two main types of nutsedge that cause problems throughout the United States. Yellow nutsedge can be found across the country, while purple nutsedge is primarily found in warm, humid southern states.

Nutsedge has triangular stems with waxy grass-like leaves. Both have underground root systems containing rhizomes and tubers. On yellow nutsedge, tubers form at the end of white rhizomes, while on purple nutsedge the tubers form along brownish rhizomes. They can also be distinguished by their flower colors. Yellow nutsedge has yellow flowers, while purple has red-purple to brown flowers.

“The problem with (nutsedge) is they are very upright and waxy,” says Obermann. “The herbicide can run off of them (because) they’re not laying flat.”

The key to controlling nutsedge is to apply product in mid-to-late spring before it starts producing more tubers, says McAfee. It usually takes more than one application.

Since the weed can be found across the country, certain products work best in specific grasses, making it important to read the label on whatever you choose to use.

Nutsedge can be controlled pre-emergently and post-emergently. For purple nutsedge, experts recommend the active ingredients: trifloxysulfuron-sodium, sulfosulfuron, halosulfuron methyl and sulfentrazone. For yellow nutsedge, experts recommend: sulfentrazone and halosulfuron methyl, sodium bentazon, and sulfosulfuron.


Virginia buttonwood

Virginia buttonweed is a spreading perennial that has branching hairy stems. It can be identified by its dark lance-shaped leaves and tubular flowers, which are white to purplish and grown on the leaf axis along the stem.

Virginia buttonweed has been found as far north as New Jersey, but is a larger problem for green industry professionals in the Southeast and Mid-Continent regions.

“Virginia buttonweed thrives in poorly drained soils,” says McAfee. “To effectively control this weed, poor drainage problems and/or even irrigation must be corrected.”

Chemical applications should be applied to the weed in early to late spring. Like most warm season perennial weeds, it can be difficult to manage during summer months.

McAfee says repeat applications of products with the active ingredients metsulfuron-methyl has provided good control of Virginia buttonweed in St. Augustinegrass, as well as other warm-season turfgrasses such as bermudagrass and zoysiagrass.


Spurge

Spurge can be found throughout the United States and, particularly, is a headache in the Southeast portion of the country, including Florida.

“It’s a summer annual, and what happens is it germinates in the spring but it really starts growing quite fast and it proliferates and really does well in the summer,” says PBI/Gordon’s Obermann. “In the summer it is generally hot and dry. Even though that plant is there and looks healthy, it’s still stressed and it doesn’t take in the herbicide well.”

To control spurge, it’s best to treat the weed pre-emergently, says Bell, with Dow AgroSciences. He recommends tank mixing the active ingredients dithiopyr and isoxaben to apply.

“Spurge, if you miss it from a preemergent standpoint, if you miss it when it’s very small … and even if you go after it from a postemergent standpoint, or a hand weeding standpoint, you really have to get the entire plant down to the root,” Bell says.

“If you snap off a piece of it or you don’t get enough chemical absorption of the plant, the plant will reproduce and it’s really aggressive from a growth standpoint,” he continues.


Wild violet

This cool season perennial broadleaf weed is found in mostly wet, shaded areas in the Mid-Continent and North Central regions. It can grow 2- to 5-inches tall and has leaves that vary but are generally heart-shaped. Its flowers range in shades of white, blue and purple and appear in March to June.

“Wild violets are very difficult; they have a deep taproot and fibrous root system,” says Obermann, with PBI/Gordon. “They get a thick waxy leaf on them that is almost like a repellent to herbicides.”

Wild violets can be controlled by treating them in the spring when they begin to bloom and before their leaves form that waxy texture, and then again in the fall.

Gardner,  with Ohio State University, says they used to recommend treating wild violet’s in November, but in the North Central part of the country, many times the leaf tissue has eroded and is no longer above the surface of the ground, making it difficult to actually kill the weed.

Gardner says a spring application is needed. He recommends the active ingredients aptexor, dicamba, triclopyr or both dicamba and triclopyr mixed together.

Metsulfuron-methyl can be used to control wild violets in bermudagrass, St. Augustinegrass and centipedegrass, says McAfee, with Texas AgriLife Extension Service in Dallas. For cool season lawns, triclopyr plus phenoxy and products that contain fluroxypyr plus phenxoy are usually effective.


Before you treat
The weeds still aren’t dying? Here are a few more tips.

  • Many times the weed has been misidentified. University websites and the U.S. Department of Agriculture’s PLANTS Database are good tools for correct identification.
  • “One of the biggest mistakes I’ve seen in my career is people will misidentify a weed that is not on the label,” says Matt Bradley, herbicide product marketing manager, Bayer Environmental Science.
  • Weeds can become tolerant to herbicides. “A good rotational program, mixing up modes of action, and different active ingredients is always a key to manage through those answers,” Bradley says.
  • Watch your mowing height. If grass is cut too short, it can increasee competition between grass and weeds.
  • Try to control the weed pre-emergently. Once the hot and dry months arrive, weeds, like all plants, slow down and stop taking in any products applied.