• Treat broadleaf plants with sprays that do not harm grass.Dandelion image by Andrey Kobyak from Fotolia.com
  
  Spray herbicides that deal with weeds are generally classified into two types: preemergent herbicides that affect seeds and postemergent herbicides used to kill growing weeds. Most weeds in turf are broadleaf plants such as dandelions, clover, ground ivy and knotweed. Weedy grasses include crabgrass, annual bluegrass and quackgrass. Effective weed control depends on proper identification, according to specialists with the University of Minnesota extension service.
  
  

Know What Weeds to Spray

• In addition to what herbicides to spray on weeds, knowing what kind of weed you are dealing with and when to spray helps control weeds. Perennial weeds live more than two years and seed every year. Biennials live two years, storing food the first year and sprouting seed in year two. Annual weeds complete a life cycle in one year. Summer annuals start in the spring, while winter annuals start growing in the fall.
  
  The type of weed determines the type of herbicide. In its article "Broadleaf Weed Control For Home Lawns," the Ohio State University extension service provides several ways to identify different weeds. If you do not know the type of weed, consult garden center personnel, your county extension agent or plant diagnostic clinics, usually found at state agricultural colleges and universities.
  
  

Preemergence Weed Sprays

• Preemergent herbicides prevent weeds from germinating in turf. Preemergent controls stop weed root development, and the weed dies shortly after germination. According to the Ohio State University extension service, ingredients in preemergent herbicides for annual weed grass control include benefin, bensulide, DCPA, pendamethalin, oxadiazon and siduron. Of these options, siduron is applied at the time of seeding, according to the extension service. Siduron also provides control of annual grass weeds without injuring seedling turf grasses.
  
  

Postemergence Weed Sprays

• Postemergent herbicide weed sprays normally combat broadleaf weeds that are not controlled with preemergent spray applications. Some effective postemergent sprays against broadleaf weeds are 2,4- D, 2,4-DP, MCPP and dicamba. All of these chemicals are safe on Kentucky bluegrass, perennial ryegrass, tall and fine fescue. MCPP is safest for bentgrass lawns, according to the Ohio State extension service. Weed identification is important because application times range from early spring to late fall, depending on the weed.