Weed Control/Herbicides
 Clover (broadleaf weed) |
 Annual bluegrass (grassy weed) |
 Crabgrass (grassy weed) |
Sometimes you can do all the cultural practices just perfectly and still have weeds in the lawn. To kill the remaining weeds herbicides are recommended. A herbicide are a chemical compound designed to kill unwanted plant life. There are two types of herbicides preemergence and postemergence.
Preemergence herbicides affect germinating seeds. To be effective, the herbicide should be applied two to three weeks before weed seeds germinate. Consequently, preemergence herbicides are most effective against annual weeds.
Post emergence herbicides are used to kill weeds after the weed plants are up and growing. To be effective, most postemergence herbicides must be absorbed through leaves; consequently, liquid sprays generally work better than dry, granular materials. However, granular formulations may be the most practical way for homeowners to apply these materials.
Postemergence herbicides are most effectively applied when weeds are young and growing vigorously.
Selective postemergence herbicides are usually used to control annual, biennial, and perennial broad-leaved weeds because they will kill many broadleaf plants without damaging grass plants. These herbicides can severely damage or kill trees, shrubs, and flowers; thus, they should be used with great care near these plants.
 Barnyardgrass (broadleaf weed) |
 Spurge (broadleaf weed) |
Postemergence herbicides may be applied any time the weeds are actively growing, the air temperature is 60-80 degrees F, there are no winds, and there is no rain in the forecast for 48 hours. Most effective control of perennial broadleaf weeds is obtained when applied in early fall or in spring. For some weeds, repeated application at 20-30 day intervals may be required for control.
Nonselective postemergence herbicides kill all plants, both desirable and undesirable. These herbicides can be used to spot treat perennial grassy weeds that are not affected by selective herbicides. To spot treat an area, thoroughly wet the weed foliage with herbicide solution.
Preemergence or selective preemergence granular materials may be applied with a fertilizer spreader. The spreader must set or be calibrated to apply recommended rates. The preferred method of application is to apply one-half the recommended rate in one direction and one-half at a right angle to that direction.
Compressed air sprayers or sprayers attached to a garden hose are effective for liquid applications. Remember that the higher the pressure and the finer the mist, the more likely it is that the herbicide will drift and injure shrubs, trees, flowers, and vegetables. Sprinkler cans can be used on small areas, but once any applicator has been used to apply herbicides, it should not be used to spray other pesticides on ornamental or garden plants. You should use a separate sprayer for killing weeds. Be sure to clean the sprayer thoroughly after each use.
| Broadleaf weeds | |
|---|---|
| Dandelion (P) Dock (P) Plantain (P) Purslane (P) Thistle (P) Black Medic (A) Chickweed (A or P) Clover (P) Ground Ivy (Creeping Charlie) (P) Henbit (WA) Knotweed (A) Mallow (A or P) Spurge (A) |
These weeds are best controlled by selective postemergence herbicides. Early fall is the best time to control winter annual (WA) and perennial (P) weeds. Spring is the best time for summer annual (A) weeds. Apply when soil is moist and weeds are young and actively growing. Dicamba can be dangerous to trees and shrubs because it can move in the soil and be taken up by tree shrub roots. |
| Grass weeds | |
| Annual bluegrass (A or P) Barnyardgrass (A) Crabgrass (A) Foxtail (A) Goosegrass (A) |
Use preemergence herbicides. Apply two to three weeks prior to expected germination of weed seeds. Some of these herbicides may injure fine fescues or bentgrasses. Most preemergent herbicides will harm newly seeded grasses except siduron. |
| Bromegrass (P) Quackgrass (P) Tall Fescue (P) Creeping bentgrass (P) |
These weeds can be controlled only with nonselective herbicides. Spot treat only because herbicide will also kill desirable grass plants. Apply when weeds are actively growing. |
| Key | |
| A = Annual P = Perennial WA = Winter annual Read and follow the label directions for the use of all pesticides. |
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