I have new seeded grass and weeds are starting to grow. What shall I use to control weeds and not kill the grass. Webb
Whenever soil is disturbed the result is weeds. There are two types of weeds that you will be dealing with. One is the broadleaf weeds such as dandelions, henbit and chickweed. Many of these are starting to flower now. If the grass was seeded last fall and you have mowed the new grass a couple of times than any of the broadleaf herbicides will work. If the grass was seeded this spring then at this point timely mowing is your friend. Most broadleaf herbicides cannot be safely applied until the new seedling grass has been mowed at least twice.
The other common weeds are the annual grassy weeds such as crabgrass. These have not started to germinate yet. These weeds are easier to control thanks to a pre-emergent product that contains Dithiopyr or that is sold under the name Dimension. Most labels state that it can be applied after the new seedlings have been up for about two weeks. This product also works on newly germinated crabgrass. Many years it can be applied into early May and still provide excellent annual grassy weed control.
Be sure to read and follow all label instructions when applying on new grass. These suggestions are options but the label is the law and will have the fine details to make sure the lawn is not damaged. Hope this helps – Dennis, Johnson County Extension