Hard to control weeds
I have weeds on the lawn that survived weeds control sprayed by Trugreen. These weeds have shallow roots and can easily be pulled off by hand. But there are just too much of them all over the lawn. What's the name of the weed? What can I use against them? Thanks if you can provide some ideas.
This is Japanese stiltgrass. The most effective way to control it would be with a preemergent herbicide labeled for crabgrass control. Apply prior to crabgrass germination in the spring when soil temperatures are above 55° to 60°F for 7 to10 days (during and shortly after, forsythia bloom is a rough, but not consistently reliable, guide for application timing). Water after application, according to the label. A second application may be possible, usually 6-8 weeks later (see label).
Currently there is no type of selective postemergent herbicide available for this particular weed. It is an annual, so it will die back in the winter. Take a look at the following web page for additional information: https://extension.umd.edu/hgic/japanese-stiltgrass
Maintaining a dense turf is one of the best ways to prevent this weed from getting established. We recommend that you overseed in the fall to thicken up the lawn. A certified tall fescue seed is highly recommended for Maryland lawns. The following fact sheet provides information about lawn renovation and overseeding in the fall. https://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG102%20L...
Thank you so much for the detailed answer. Questions about over-seeding this fall: When is the best time to seed? How long should I wait after a weed control spray? What type of seed will result in fine-blades and thick turf in our region (my current somewhat thinning lawn grass has fairly thick blades)? What to use in shady areas under a lot of tall pine trees? Is it necessary to aerate first?
Late August through the cool of fall is the best time to seed.
The recommended grass for area lawns is Turf-type tall fescue.
In shady areas, go with a mix of fine fescue. Heavily shaded areas with lots of root competition may do better with mulch or groundcovers.
Core aeration done before seeding does help.
Take a look at this publication that has all the info you need to get it done: