About Weed Killers

• No single type of herbicide will control all kinds of weeds at all times, according to the University of California website. Three basic types of weeds are a problem in lawns: broadleaf weeds, grasses and sedges. Try to identify the weeds before choosing a weed killer to avoid using adding unnecessary chemicals to the environment. Timing is an important factor in killing weeds in lawns. Preemergent herbicides are effective before weeds begin to sprout in the grass. Postemergent herbicides work on weeds that are already visible. Apply the right type of weed killer at the right time of the year. Ortho Weed B Gone, for instance, is a postemergent herbicide that kills weeds that have already sprouted.
  
  

Using Weed Killers

• Some weed killers are broad-spectrum herbicides; that is, they kill a variety of weed types effectively. Other types of weed killers kill specific types of weeds. This is why identification of the weeds in your lawn is so important. Identification will help you choose the most effective herbicide for your lawn. Ortho weed killers come in a variety of formulas specifically designed for different kinds of weed problems, such as crabgrass, nutsedge, clover, oxalis and other weeds.
  
  

Application Frequency

• The frequency of use of weed killers depends on many factors, including whether they work on unsprouted weeds or weeds that are already in evidence. Ortho Weed-B-Gon Max for Crabgrass, for instance, is used on growing weeds and can be used as frequently as every two weeks. The company does recommend that you not use the product more than twice per year. Ortho Weed-B-Gon Max for Southern Lawns recommends a repeat use in two to three weeks after the first application.
  
  

Precautions

• Some types of grass, such as St. Augustine, also called Floratam grass, can be damaged by weed killers. Do not use Ortho Weed-B-Gon Max on St. Augustine grass or centipedegrass, according to the Scott's site. Read the labels of weed killer carefully to make sure the formula is safe for use on St. Augustine grass. This weed killer should be used when the temperature is below 90 degrees Fahrenheit. Do not used on newly seeded lawns until the grass has become established.