October 25, 2014

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Options for controlling weeds in your lawn this summer

Yes, I said summer!  With temperatures in the mid-80’s and dew points approaching 70 degrees, I think it’s safe to say that summer has finally arrived.  With the arrival of summer, we also notice that many weeds are starting to show themselves in Minnesota lawns.  The late winter (or cold spring…..whatever you want to call it) left many of us scratching our heads wondering if our turf would have a chance to wake up and grow before the weeds took over.  There was a very short window to give our turf that “edge” this spring.  The edge involves providing a proper growing environment for our species of turf; this means proper fertility, aeration, irrigation, and the many other practices that encourage a healthy lawn.  I’m a firm believer in the old adage that a healthy lawn is the best defense to weed invasion, but that doesn’t always go as planned.  Still, you have options.

Step 1: Identify the weed species that you’re trying to control.    

smooth crabgrass

The distinct growth habit of a mature smooth crabgrass plant. Post-emergent herbicide control is less effective when crabgrass reaches this stage

Turfgrass weeds can be grouped into two basic categories when discussing control options: grassy weeds and broadleaf weeds.  Grassy weeds present the biggest challenge for control in home lawn situations because their growth physiology is similar to that of the turfgrass being grown.  Some grassy weeds to look for at this time of year include: the summer annuals- large and smooth crabgrass, winter annual- annual bluegrass, and the perennials- quackgrass and yellow nutsedge.   

If you missed the crabgrass pre-emergent window (which by now has passed in many areas of the state), this grassy weed can still be controlled with selective post-emergent herbicides containing the active ingredients quinclorac or fenoxaprop.  Effective crabgrass control is best accomplished when plants are in the juvenile stage, as mature plants are less susceptible to herbicide injury.  Turfgrass tolerance to these herbicides is reduced in the heat of the summer.

prostrate spurge

Prostrate spurge is a summer annual commonly found in Minnesota lawns. It can be identified by the milky white sap that appears when the stem is broken

Broadleaf weeds are much easier to identify and control.  Some broadleaf weeds to look for at this time of year include: summer annuals- prostrate knotweed and prostrate spurge, the perennials- dandelion, broadleaf plantain, ground ivy, and white clover.

For an identification guide to common lawn weeds in Minnesota, visit:

Is This Plant A Weed?

Step 2: Evaluate control options, whether cultural or chemical.  Cultural control involves hand weeding, followed by creating an adequate growing environment for the turf species present.  Often times we hear of certain weeds being labeled as ‘indicators’ for poor site conditions.  Correcting these site conditions can have a dramatic impact on your weed reduction program.  Examples of indicator weeds: low nitrogen situations- clover and black medic, shaded conditions- ground ivy and wild violet.

Some weeds lend themselves to be pulled readily by hand, especially the bunch-type grasses (ex: tall fescue) or the rosette forming broadleaves (ex: curly dock and broadleaf plantain).

When all else fails, herbicides might be your best option.  So what’s available to you? 

Selective grassy weed herbicides:  As previously mentioned, grassy weeds will be the most difficult to control due to lack of effective herbicides.  For post-emergent crabgrass and other grassy weed control, fenoxaprop-P-ethyl (Bayer Crabgrass Killer for Cool-Season Lawns) or quinclorac (Bayer All-In-One Weed and Crabgrass Killer, Ortho Weed-B-Gon + Crabgrass Killer, others) are effective for control.  Quinclorac will also control some broadleaf weeds such as clover and dandelion.

Selective broadleaf herbicides: Combination products are available for broadleaf weed control in home lawns and most are very effective.  These products generally include two or more of the active ingredients: 2,4-D, dicamba, MCPP, triclopyr, carfentrazone, or sulfentrazone.  Follow specific label instructions to target the broadleaf weeds that you are dealing with.   

Non-selective herbicides: Many grassy weeds cannot be controlled selectively in home lawn situations.  In this case, the use of non-selective herbicides and re-seeding will be required.  Non-selective herbicides available include: glyphosate (Roundup), glufosinate (Finale), and diquat.  As with all herbicides, be sure to follow the manufacturers label and recommendations.            

prostrate knotweed

Prostrate knotweed is a summer annual and the first weed to germinate in the spring. This weed is generally an indicator of compacted soils.

 

Step 3: Learn to understand the ‘indicator’ weeds in your lawn.  Create the best growing environment possible with proper fertilization, irrigation management, and turfgrass species selection.  Remember the six basic requirements for plant growth: air, water, light, nutrients, space, and temperature.  Keeping all of these as close to optimum for the turf species in your lawn will be your best defense against weed invasion.  You are not alone in this battle, putting in the extra effort to create a healthy lawn from the start will save you from playing catch up down the road.  Good luck!

For more information on weed control options, visit:

Control Options for Common Minnesota Lawn and Landscape Weeds