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Homeowners Lawn Care Water Quality Almanac

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April    Watch for Weeds
Establish thresholds for action 
  • A weed is a plant growing in the wrong place.
  • Bare spots or thin turf will allow weeds to grow. The best defense against weeds 
    is a vigorous, dense stand of turfgrass.
  • Before choosing a weed control option, make sure you know what weeds you have.
  • Decide which species you can live with and which species you want to control.
  • If you decide you can’t live with a particular species, determine how many you need to see before you choose a control measure.
Keys to Good Mowing: Proper mowing reduces many weed problems
Keys to Good Mowing
Set mower height to 3 in. or higher.
Keep blade sharp; sharpen after every 4 hours of use.
Follow the 1/3 rule: remove only 1/3 of grass height with each mowing.
Keep clippings on lawn.
  • If populations surpass your thresholds, make sure the control you choose is appropriate for the weed’s unique life cycle and biology.
  • Annual weeds die off and leave bare soil that is prone to increased runoff.
  • Perennial weeds, if dense, can assist in maintaining density and minimizing runoff.


Perennial Weeds
Dandelion Ground Ivy Clover Plantain Nutsedge
Dandelion Ground Ivy Clover Plantain Nutsedge

Annual Weeds


Annual Bluegrass
Annual Bluegrass

Knotweed (Indicates comapction)

April is a good time for

  • Mowing: Begin when turf is 4 to 4 1/2 inches tall. Set mower height to 3 inches. Remove only one-third of the overall grass height with each mowing.
  • Fertilizing: Don’t fertilize yet if your lawn looked good after winter and/or you fertilized in late fall. Excess fertilizer in early spring promotes top growth at the expense of root growth. Deeper roots are more resistant to pests and drought.
  • Seeding: Seed only if you have a thin, weak lawn or bare spots. Depending on 
    the species, grass will germinate when soil temperatures reach 45 to 55° F at the 2-inch depth.
  • Irrigating: Spring rains should be sufficient.
  • Monitoring soil temperatures: Insert a thermometer to 2 inches and wait 5 minutes.
  • Scouting: Search for large grubs, but do not apply insecticides because they will not be effective.
Weed Control Options
Cultural: Try these techniques first if you have more weeds than you can tolerate.
  • Mow at the proper height for the species of grass. Mowing higher helps desirable turf shade weeds out.
  • Reduce soil compaction around areas of heavy wear.
  • Weed by hand (best when soil is slightly moist).
  • Reduce soil compaction adjacent to paved areas.
  • If lawn is thin, fertilize to improve density


Preemergence herbicides (most common for crabgrass, goosegrass)

  • are applied to the soil before weeds are expected. 
  • have low solubility and bind to organic matter, thus they have high runoff potential unless watered in properly.

Postemergence herbicides (most common for perennial broadleaf weeds)

  • are applied after weeds have emerged.
  • have high solubility and thus high leaching potential, and do not bind to organic matter. Avoid applying before intense irrigation or rainfall.

Nonselective herbicides

  • kill or injure all plants they come in contact with. 
If you choose a pesticide, be smart:
  • Use the right product at the right time. Follow label directions and keep accurate records to create a history.
  • Choose products that have the least potential for leaching into groundwater. More highly water soluble materials have the highest potential (e.g., 2,4-D, dicamba, MCPP).
  • Use extreme caution when handling materials close to wells and impervious surfaces where runoff may enter storm sewers.
  • To avoid volatilization and drift, which release pesticides into the air, do not spray when temperatures are high or it is windy.
  • To help prevent polluted runoff, do not apply pesticides when heavy rains are expected or the ground is already saturated or frozen. Studies have shown that 80 percent of lawn runoff occurs when soil is frozen.
  • Empty containers should be triple rinsed and disposed of properly.  Unused materials should be returned in the original container to authorized hazardous materials collection sites.

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This page last updated on
November 05, 2000

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