How do I control perennial grassy weeds in the lawn?

Question: 

How do I control perennial grassy weeds in the lawn?

Answer: 

Perennial grassy weeds die back to ground level in fall but send up new growth in spring.  These weed species have long narrow 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 zoysia grass.

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. 

Perennial grasses, such as quackgrass and nimblewill, are some of the most difficult weeds to control in the lawn. Control is difficult because there are 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. 

Herbicides

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.

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