Many things should be done before hauling out the sprayer and purchasing herbicides to control undesirables in your lawn. If you do the cultural management for lawn establishment and maintenance that we emphasize in our Master Gardener core turf class, half the battle - or more - is won. So let us review a few of the important cultural practices that suppress undesirable weeds.
First, when establishing or renovating a lawn, get a soil test. Review University Extension guides on how to do this properly or ask. The time to correct problems, especially issues such as low soil phosphorous or acidity problems is when some tillage is done. Phosphorus and lime do not move down into the root zone very well.
Then be prepared to seed with enough seed or reseed in a uniform fashion, assure good seed - soil contact, irrigate as needed and prevent erosion. Fall (September and October) seeding generally works better.
After establishment, mow frequently at a higher height, taking no more than a third off the top at a time. Remember dominant cool season grasses' - including fescues and - root systems grow in proportion to the growth above ground. So, if the grass canopy is a bit taller, the root system is likely to be more expansive. This helps with nutrient absorption and water uptake. A taller height also can inhibit germination of some weed seeds and helps the turf compete with weeds better. Take a look at your local bank or other commercially, well-managed lawns and get out there with a ruler to see how high they mow. You will likely find fescue is 4 inches tall and bluegrass may be 3-3.5 inches tall.
If you need croquet court or putting or chipping turf quality, then putting down crabgrass preventer between April 1-15 is advised (see column continuation below). For broadleaf weeds like dandelions, apply lawn herbicides (which mean they kill common broadleaf weeds lawn weeds like dandelions and chickweed but don't harm grass) safely in the spring or fall. Some of these "lawn herbicides" are in a granular form and are often combined with fertilizer for a single "weed and feed" application. If using these, be sure to carefully read the label for correct application, as they generally require free moisture (such as heavy dew or a recent rain) to activate and work as promoted. Spot spraying, with lawn herbicides that are mixed up from a concentrate, is a good way to apply less. One down side to the various lawn herbicides is they will inhibit or harm new grass seeding. So read the label, and plan your management.
Controlling crabgrass after emergence
We are now well after the date to "prevent" crabgrass from germinating/emerging (as noted above as before April 15). If you've missed that date, you may be asking, what can I do? And if you have some other traditional broadleaf lawn weeds (i.e., dandelions) you may be thinking, "Wouldn't it be nice to kill both crabgrass and dandelions at the same time?" Well, the good news is, now there are some products available.
Look for products that say they kill both lawn weeds and crabgrass. If it does, check the active ingredient list - it should include quinclorac as one. I checked with the University of Missouri turf specialist about these products, and his signatory advice was "the key with any of these combination products is to control weeds when they are small." He went on to say folks want to use them well after the weeds are established and do not get the control they desire.
The downside to these products is they need to be applied as a spray. To make that more convenient these may be sold in a bottle with a hose end attachment. For someone with a smaller lawn, around 5,000 square feet or smaller, this is fine. But when a lawn size swells to 10,000 square feet or more, spraying that much area is a lot of work, thus the advantage of granular-applied products.
The Central Missouri Master Gardeners hotline is staffed from 12:30-4:30 p.m. Tuesdays and Fridays; call 634-2824 then or anytime to leave a message. The Central Missouri Master Gardeners are a volunteer group of 191 members, 122 of whom are Cole County residents, who maintain 11 beautification sites in Cole County. Master Gardeners must complete a basic training program of at least 30 hours of horticultural training including landscaping, lawns, vegetables, flowers and fruits, as well as 30 hours of volunteer service.
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