Healthy grass can tolerate moderate levels of insect or disease infestation. However, even the healthiest lawns sometimes need pest control to prevent significant grass damage. Correct and judicious use of chemical or biological pesticides will reduce pest populations and allow grass to recover. Lawns that are properly maintained with appropriate but modest use of fertilizers and pesticides will do more to protect water resources than to harm them.
Follow pesticide label directions exactly. The label provides essential information on product application and proper container disposal. Label contents are prescribed by law, and must be followed exactly. Never pour pesticides in a storm sewer or onto sidewalks, driveways or streets.
Remember, you may or may not need a pesticide. Before applying an insecticide or fungicide to grass, be sure the apparent damage is being caused by an insect or disease. Then choose the best control method.
When applying pesticides, timing is everything. It is best to treat pests when they are young or in a highly vulnerable stage. Once weeds or insects are quite large and mature, greater amounts of pesticides are usually needed—but may not be as effective. Fungicides work the same way: treating disease problems at very early stages of infection is more prudent and may require less fungicide than attempting treatment of large, heavily infected areas.
Weeds should be identified to determine whether applying herbicide is necessary. The presence of weeds may indicate that other conditions need to be corrected.
Fall is the best time to control perennial broadleaf weeds such as dandelions, plantain, clover and creeping charlie. From mid-September to early October, broadleaf weeds grow actively and will readily take up herbicides—a single application of an appropriate herbicide is often effective. By mid-September, there is less chance of injury to garden plants. However, that does not give license to be careless when applying pesticides.
Sometimes a pesticide must be watered into the soil to be effective. For example, pre-emergent herbicides used for controlling crabgrass and other annual weeds must be watered into the soil, since they affect seeds as they begin to germinate. Products used for controlling thatch and soil-inhabiting insects and diseases usually require water after application—follow instructions on the label. This moves the product into the thatch and soil area so it’s most effective, reduces the chances of runoff, and reduces exposure to people.
Depending on your soil type, 1/4 to 1/2 inch of water should be applied after spreading a pre-emergent herbicide (that’s 1 to 2 hours with most lawn sprinklers). Automatic irrigation systems may need to be adjusted accordingly. Shallow watering puts the weed killer where it will be most effective, but far enough into the soil that it won’t be carried away by runoff.
You don’t need to drench the soil for your herbicide to be effective. Both water and herbicide may be wasted, and the herbicide may move beyond the plants and into the soil, where it could be prone to leaching. Follow label instructions for proper mixing and water volume.
Minnesota Department of Agriculture (MDA), 625 Robert Street N, St. Paul, MN 55155-2538, firstname.lastname@example.org