From Dennis Patton:
The garden centers have been abuzz this fall with the sale of grass seed. It is almost like the holiday shopping season, only so many days and so much to do. Homeowners that have overseeded this fall are often confronted with more challenges than just seeding and achieving a good stand of grass. Lawn weeds also invade these thin lawns.
There are many questions and concerns associated with newly seeded grass and the application of herbicides to control weeds. Weed control with new grass should be approached with caution. Attempting to improve the quality with an ill-timed application can destroy a lot of hard work.
As a general rule of thumb, when it comes to weed control and new grass, the best recommendation is to wait. Herbicides applied too soon after grass germination can have adverse effects, such as killing the young stand or weakening it, thus greatly reducing the amount of time it takes to fill in. The information you need for timing is on the product label. Read and follow all label instructions.
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Most herbicides have a waiting period between grass germination and application, normally after two mowings of the new grass. Keep in mind this two-mow rule is for the new grass, not the established lawn being seeded into. After this point the roots have established and the crowns have matured enough so there is no effect from the chemicals. This waiting time is true of most broadleaf herbicides. Once again, read the label.
In addition to the waiting time after germination, there is also time for a last application before seeding. Chemical applied four to six weeks before seeding can also have adverse effects on the tender young grass. Proceed in the summer months with caution if overseeding is on the September calendar. Always read and follow the label instructions for the product to be used.
Cool fall conditions can slow the development of the young grass during the fall months. Often the new grass does not grow enough to reach this two-mow guideline. If this is the case then weed control will need to be delayed until spring. Normally the fall and winter growth periods will provide for the needed establishment period.
Keep in mind the best defense against lawn weeds is a thick, dense healthy stand of grass. Herbicide applications are just one option for decreasing weed problems. Good cultural practices are the best defense. No matter when chemicals are applied be sure to read and follow all labeled instructions as it provides the safety information required to achieve the desired outcomes while protecting your investment and the environment.
Did you pick up the most important part of this column? And that is, read the label.