Annual grassy and broadleaved weeds have shown up in both thin and thick lawns this summer. The good news is that being an annual they will die yet this fall. By mowing them, we have eliminated or seriously reduced adding to the seed bank for next year. The exception would be crabgrass, having adapted to mowing and produces flower and seed below our 2.5- to 3-inch cutting heights.
More troubling are the perennial grasses and broadleaves. They will be coming back regardless of being mowed or not. Some like creeping Charlie, also known as ground ivy, can flower and set seed pretty much at ground level. Broadleaved weeds can be selectively managed with the proper herbicides, if treatments are warranted. There also are organic treatments available. Depending on the weed, more than one treatment may be needed, regardless of the products used. Timing can work for you too. Treatments for dandelion control done in the fall will take out both the dandelions established in the lawn and any seedlings that germinated this spring and summer. Another reason for a fall treatment is that dandelion is one of the early sources of pollen for bees.
Control options can be done before the weed seed begins to germinate in the spring. The easy example is crabgrass preventer products. Either these stop the crabgrass seed from germinating or impact the root radicle as it emerges from the seed. Crabgrass preventers also work on other grassy annual weeds like our foxtails and goosegrass. Spending a few minutes reading the label of several products will let you know if they will control some of the broadleaf weed seed too.
Perennial grassy weeds of tall fescue and quackgrass present another challenge. Any non-selective product used to control either one also will remove the desirable grasses in the treated area. Tall fescue is a bunch-type grass and you may be able to dig it out, being generous with the distance from the plant itself if there is just one surrounded by desirable grasses. Quackgrass has an extensive root system that will spread several feed from the established plant.
If the lawn has been thinned by annual grasses, promote thickening by topdressing and reseeding. As dandelions fade away, the lawn can fill in those single plant voids between this fall and next spring. If there are many failing dandelions, the topdressing and reseeding technique should be used. A fall fertilization also will promote new seedling growth and thickening of existing lawn grasses. Any time seed is added to the lawn and buffed in to the topdressing it must be kept moist for successful germination.
Richard Hentschel is a Horticulture Extension Educator with University of Illinois Extension, serving DuPage, Kane and Kendall counties. Stay tuned to more garden and yard updates with "This Week in the Garden" on Facebook at facebook.com/extensiondkk/videos. The 2017 Kendall County Master Gardener Help Desk currently is open Monday, Wednesday and Friday from 9 a.m. to 12:30 p.m. at 630-553-5823 or at uiemg-kendall@illinois.edu.