How do I control perennial grassy weeds, like quackgrass, zoysiagrass, or nimblewill in my garden and lawn?
Perennial grassy weeds die back to ground level in fall but send up new growth in spring. These weed species have long thin leaves with parallel veins. They are often in the poaceae (grass) family or a closely related family and are botanically classified as monocots. Perennial weeds reproduce by seeds or may spread by creeping above or below ground stems or by spreading root systems. Examples of perennial grassy weeds include, quackgrass, nimblewill, orchard grass, and in certain cases bermudagrass and zoysiagrass.
Keeping ahead of weeds and controlling them when they are small is essential for good weed management. This requires persistence throughout the entire growing season to remove weeds as they emerge.
Cultivation, hand pulling, mulches and herbicides are the primary means to control weeds in the home garden.
Management in Vegetable Gardens & Garden Beds
Pulling & Digging
In small areas, some weeds can be controlled by pulling and digging. This method is best accomplished after a soaking rain or deep watering. It is essential that the entire plant and root system is removed. Any remaining root fragments will usually resprout and grow. This can be difficult and requires persistence to be effective. Pull or dig weeds when they are young before they become established.
Mulches control weeds by preventing the germination of weed seeds. They can be effective at preventing new perennial weeds from germinating, but are less effective on those weeds that are already established and can spread by rhizomes and stolons. Established weeds should be destroyed prior to the application of the mulch. Grass clippings, shredded leaves, coco hulls and weed-free straw are excellent mulches for vegetable gardens and annual flower beds. Apply several inches of these materials in early June after the soil has warmed sufficiently. Wood chips and shredded bark are excellent mulches for perennial beds and areas around trees and shrubs. Apply 2 to 4 inches of material around landscape plantings. These materials decay slowly and should last several years. However, it will be necessary to apply additional material periodically to maintain the desired depth.
In some situations, herbicides are the only practical and efficient method of control of grassy perennial weeds. For these weeds, spot treatment with a non-selective herbicide is often the only herbicide option. Non-selective herbicides, like glyphosate, kill any green plant material they contact so careful application is necessary to not affect nearby desirable plants. Grass selective herbicides are available. They include fenoxaprop-ethyl, fluazifop-p, sethoxydim, and clethodim. Consult the label carefully as they are not labeled for all garden settings can can negatively impact desirable plants if applied incorrectly.
Always apply herbicides when winds are calm and temperatures are cool to prevent drift and damage to desirable plants. Protect garden plants with barriers like buckets or boxes to further reduce problems with drift. They can also be applied with a sponge and wiped onto the leaves of the weed to prevent collateral damage to nearby plants.
For best control, apply herbicides in spring or fall. Since herbicides are more effective on small plants, spring applications are beneficial for killing weeds before they become large or flower and set seed. Many grassy weeds are warm season grasses that green up later in the spring than cool season grasses. Be sure the weedy grasses that need control are actively growing before application. Most herbicides are absorbed and translocated throughout the stems, leaves, and root system to completely kill the weed. In fall, plants naturally move carbohydrates from stems and leaves to the roots. Often a more complete kill of the plant is observed with fall applications of herbicides because it takes advantage of this natural movement in the plant.
Herbicides must be used according to label instructions on the package. Failure to follow directions may kill desirable plants or prevent other plants from being grown in the area.
Management in the Lawn
Perennial grasses, such as quackgrass and nimblewill, are some of the most difficult weeds to control in the lawn. Control is difficult because there very few herbicides available to homeowners that will selectively destroy these weeds and hand digging is difficult.
Pulling & Digging
Pulling or digging these perennial grasses is possible, but can often be unsuccessful if the entire plant and root system is not removed. Any remaining root fragments or plant pieces will usually resprout and grow. This method is best accomplished after a soaking rain or deep watering. Pull or dig weeds when they are young before they become established to make removal easier and more complete. Management utilizing hand pulling and digging requires persistence to be effective.
Typically the most effective way to control perennial grassy weeds in the lawn is to spot treat the weed-infested areas with a non-selective herbicide like glyphosate. A few species of perennial grassy weeds in cool-season lawns can be managed with a selective herbicide. These herbicides are often only available from professional lawn care services and must be applied by licensed applicators.
Midsummer is an excellent time to control undesirable perennial grasses in the lawn. Most perennial grasses are actively growing in summer. Also, midsummer control efforts allow adequate time to kill the weedy grasses and to prepare the areas for seeding or sodding in late summer. Spray the weedy patches and a few inches beyond these areas to ensure their complete destruction. If the treated areas are not dead in 2 to 4 weeks, a second application is necessary. Treated areas can be seeded or sodded 7 days after the application.
After the treated areas have been completely destroyed, reestablish the lawn by seeding or sodding. If you plan to sow seed, it's not necessary to dig up the destroyed areas. Small areas can be raked vigorously with a garden rake to remove some of the dead debris and to break the soil surface. After seeding, work the grass seed into the soil by lightly raking the areas. Large areas can be seeded by a turf-type or slit seeder. A turf-type or slit seeder cuts small grooves into the soil and deposits the seed in these grooves. The best time to sow grass seed is mid-August through mid-September. After seeding, keep the soil moist with frequent, light applications of water.