Fact Sheet Crabgrass and Weed Control in Lawns

Crabgrass Control Crabgrass is present every season and was more so this year in lawns that were damaged by drought during the fall of 1998. Crabgrass seeds germinate when the temperature in the upper inch of soil reaches 50F to 55F for at least five consecutive nights under moist conditions. Exposure to sunlight is also critical to seed germination. This is why thin lawns are more susceptible to crabgrass infestation. The best method of crabgrass control is by applying preemergent herbicides. The application deadlines for preemergent controls are normally March 1 to April 1 for southern Ohio. For northern Ohio, dates are April 1 to May 1, and for central Ohio, they are March 15 to April 15. For other parts of the country use the 5 50 degree nightime soil temp as a rule for application.During the week of April 29, crabgrass germinated in the Ohio State University turf plots in Columbus, Ohio. Once crabgrass had germinated, Dimension (dithiopyr) was recommended. Good crabgrass control was achieved when Dimension was applied prior to the three- to five-leaf to one-tiller stage. Siduron (e.g., Tupersan) was the only safe preemergent material recommended for crabgrass control in areas newly seeded this spring.Once crabgrass passed the two- to three-tiller stage, Acclaim or Acclaim Extra (fenoxaprop-ethyl) was recommended as the postemergent product for later stages. Acclaim or Acclaim Extra can be mixed with a preemergent product as well. Drive (quinclorac) was suggested as another good postemergent control with rapid kill. It works on mature crabgrass and can be mixed with a preemergent control material. Drive can also be mixed with phenoxy herbicides (e.g., 2,4-D) for broadleaf weed control while Acclaim and Acclaim Extra can not. Drive does a good job under adverse conditions, such as dry soil. There are several important facts about post-emergence crabgrass control. Drive, a post-emergence crabgrass herbicide, must be used with a surfactant to be effective. Methylated seed-oil surfactants should be used with Drive. When used with a surfactant at a rate of 1% volume to volume, it can be very effective. Dimension also should be used with a surfactant. A surfactant is not necessary when using Acclaim. Drive, when mixed with any of the broadleaf herbicides, could cause discoloration. However, turfgrass does recover. Mixing these herbicides does not affect their efficacy. Broadleaf Weed Control in Lawns The development and maintenance of a dense, healthy stand of grass is the best way to reduce the incidence of broadleaf weed problems. It is important to identify the weed(s) that you are attempting to control, since not all weed species are controlled by using one specific herbicide. The most readily available chemicals to homeowners for selective, post-emergence control of broadleaf weeds include 2,4-D, 2,4-DP, MCPP, and dicamba. These chemicals can be found in various combinations with each other. Combination products are recommended for difficult-to-control weeds or when a variety of weed species is present in the lawn. Examples of very effective product combinations are Cool Power (dicamba + MCPA + triclopyr,) and Super Trimec (2,4-D + 2,4-DP + dicamba.) Both of these products are ester formulations. All of these chemicals are safe for use on Kentucky bluegrass, perennial ryegrass, tall fescue, and fine fescue lawns if the label directions are followed. MCPP is the safest of the listed herbicides to use on bentgrass lawns.Spring herbicide applications should be made from mid-April through early June, and fall applications should be made during the months of September and October. Herbicide formulation plays a major role in determining the success or failure of broadleaf weed control in the spring. Weeds tend to absorb and translocate ester formulations more readily than amines under the cooler, more erratic weather conditions of early spring. Amines are more effective later in the spring when air and soil temperatures are warmer. In general, both amine and ester formulations may exhibit poor weed control before late March. Ester formulations may provide good-to-excellent weed control in the first three weeks in April and be superior to amine formulations. However, the effectiveness of amine formulations may equal that of esters from about late April and beyond. Postemergent herbicides should not be applied if rain is expected within 24 hours of application; nor should the grass be mowed or watered within 24 hours of application. Please note that drift from herbicide applications can damage or kill non-target plants and that dicamba should not be applied within the dripline of trees or shrubs. Dicamba can be root absorbed by these plants, possibly resulting in damage. Call For Price 440-320-7854