Annual grass weeds are grass weeds that germinate from seed, grow vegetatively, produce seed and die within a 12 month period. A number of annual grass weeds routinely invade Ohio's turfgrass areas including crabgrass, goosegrass, foxtail, barnyardgrass, fall pancium and annual bluegrass. The crabgrasses (Digitaria sp.) are the most common annual grass weeds in most lawns. Both the smooth and hairy types of crabgrass are classified as summer annual weeds. These grass weeds are considered undesirable contaminants in high quality lawns because of the lack of compatibility with the desirable turfgrasses. These annual grass weeds are usually lighter green in color, have wider leaf blades and possess more spreading growth habits than the cultured cool season turfgrasses.To ensure crabgrass and other annual grass weeds do not establish in home lawns, both important preventive and control programs must be implemented. The invasion of crabgrass and other annual grass weeds can be prevented to a large degree by maintaining a dense, healthy stand of grass. A high quality lawn will develop a highly competitive canopy which will shade the soil surface and discourage the germination and establishment of seedling annual grass weeds. Most annual grass weed seeds germinate in the top 1/2 inch of the soil.
One of the first steps in successful preventive programs is to seed or sod a properly adapted turfgrass species in the lawn. Following establishment, adequate fertilization programs and cultural practices facilitating the maintenance of a dense canopy including proper mowing practices, good watering practices, and insect and disease control programs are important.
In newly established lawns, thin lawns or unthrifty areas of the lawn where adequate density is not present to provide formidable preventive control, annual grass weed establishment should be anticipated. The crabgrass seeds in the soil begin to germinate in the spring once the soil temperatures warm to nighttime minimum temperatures of 52 to 54 degrees F for at least 5 consecutive nights under conditions of moist soils.
For homeowners who cannot satisfactorily address the control of
annual grass weeds in a preventive manner with strictly cultural
controls, the best way to stop annual grass weeds from establishing
in their lawns is through the use of preemergent herbicides.
Preemergent herbicides are chemicals that prevent the germinating
weeds from establishing in the lawn. These herbicides control annual
grass weeds by inhibiting cell division in the young root system. The
failure of the root system to develop results in the death of the
young seedling weed shortly after germination. Lawns with thin stands
of grass that do not provide 100 percent cover may require yearly
applications of a preemergent herbicide to prevent the invasion of
crabgrass and other annual grass weeds. In Ohio, dense, high-quality
lawns may not need yearly applications since crabgrass only
occasionally establishes in lawns with good density.
A number of preemergent herbicides are available to homeowners for
annual grass weed control. All of these herbicides have been tested
at the Ohio State University for several years. These approved
herbicides are listed in Table 1.
|Table 1. Preemergent Herbicides For Annual Grass Weed Control|
|Common Names||Trade Names||Control|
|Bensulide||Betasan, Pre-San||Good to Excellent|
|DCPA||Dacthal||Good to Excellent|
All of the listed products can be safely used on Kentucky bluegrass, perennial ryegrass, tall fescue and most fine fescue cultivars. Bensulide is the safest annual grass control material for creeping bentgrass lawns. If preventive annual grass weed control is desired in new seedings or where young, desirable seedling grasses are developing, Siduron is the only herbicide that will provide control of the annual grass weeds but not injure or antagonize the development of the desirable seedling turfgrasses. Siduron may be applied at the time of seeding.
Preemergent herbicides are generally only effective if applied before the annual grass weeds emerge. Therefore, early spring applications are essential if satisfactory weed control is to be achieved. Table 2. lists the approximate dates which annual grass weed germination normally begins. Herbicide applications should be completed and the herbicide watered-in at least 7 days prior to the initial germination date to allow time for the herbicide barrier to be established in the soil.
Preemergent herbicide applications for annual bluegrass control should be made in late summer or early fall.
If preventive or preemergent control strategies failed to
satisfactorily limit the establishment of annual grass weeds,
herbicides are available that will kill crabgrass after it germinates
and begins to grow. These products are referred to as "Postemergent
Herbicides." Postemergent herbicide applications should be made as
soon as the crabgrass is seen in the lawn. In Ohio, this is usually
between late May (Southern Ohio) and mid June (Northern Ohio).
Occasionally one, but generally two applications are needed to
control crabgrass. Make applications 1 to 2 weeks apart until the
crabgrass is killed. The success of the these treatments will be
greatly improved if the crabgrass is in the 3 to 5 leaf stage of
development. Once the crabgrass begins developing tillers (numerous
new stems), control is much more difficult to achieve. Repeat
applications may only provide partial control. If additional
crabgrass germinates after the applications, another series of
treatments will be necessary. The most common postemergent crabgrass
control products available to homeowners are products which contain
methanearsonate. This material may slightly discolor Kentucky
bluegrass, but no serious injury should result if used at the rate
and under the conditions described under "Directions For Use."
|Table 2. Approximate Dates For Preemergent Herbicide Applications.|
|Location in Ohio||Recommended Application Period||Approximate Initial Weed Germination|
|Southern Ohio||March 1 - April 1||April 10-15|
|Central Ohio||March 15 - April 15||April 20-25|
|Northern Ohio||April 1 - April 25||May 1-5|
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868