Weeds in Late Summer

By now, it’s possible that your lawn is overrun with weeds of all types….warm season annuals, warm season perennials, cool season broadleaves and of course, that “doesn’t fit into any group” weed known as yellow nutsedge.  What should be done?  Let’s run down a reasonable approach to each.

 

Warm Season Annuals

Plants such as crabgrass, foxtail and prostrate spurge typify this group.  These species are easily controlled with applications of preemergence herbicides such as prodiamine or pendimethalin, but by now, even if an application was made in mid April as recommended, it’s likely to be no longer effective, sort of having run out of gas.  Post emergence products have little or any effect on them at this point in the season, as they are mature and quite resistant.  Best control measures are keeping them mowed to prevent seedhead formation and hand pulling.

 

goosegrass unl

Goosegrass is a warm season annual that is tough to control.

Warm Season Perennials

Prostrate knotweed, nimblewill and zoysiagrass are quite healthy at this time of year.  The good news is that a transition can be made, spraying with Roundup, waiting 10 days, powerraking, dropping seed into the seed bed with a drop spreader, then keeping it moist, not soggy or dry.

prostrate knotweed 3

Prostrate knotweed certainly is a weed

Cool Season Perennial Broadleaves

The weed that most homeowners identify with is the dandelion, but others in this group include plantain and white clover.  The best approach at this point is to keep them mowed and plan an application of Trimec, Speedzone or Weed B Gone Maxx in mid September and early October.  Be sure to read and follow all label directions.  Hand pulling is also a recommended control measure.

dandelions in fairway brad j

Dandelions are a signature weed

Nutsedge

Not a grass, not a broadleaf, but certainly a weed, the rules/recommendation for controlling nutsedge have changed a bit.  Certainly, spraying it with halosulfuron or sulfentrazone as soon as it appears in spring is still recommended, however, the jury is now out as to when it should or shouldn’t be pulled.  The old advice was to pull it early in the season and avoid pulling after June 21, as it becomes more reproductive at that point.  However, any removal is good removal and reduction of the weed pressure is helpful in managing it.  It’s wise, however, to realize that removal of the topgrowth often leads to the release and emergence of several others in its place, so if you choose hand pulling, commit yourself to continued pulling for the rest of the season.

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Nutsedge grows quickly and can be robust.

John Fech
Horticulture Extension Educator at Nebraska Extension
John Fech is a horticulturist with the University of Nebraska-Lincoln and certified arborist with the International Society of Arboriculture. The author of 2 books and over 200 popular and trade journal articles, he focuses his time on teaching effective landscape maintenance techniques, water conservation, diagnosing turf and ornamental problems and encouraging effective bilingual communication in the green industry. He works extensively with the media to extend the message of landscape sustainability, making over 100 television and radio appearances each year.
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