CONTROLLING WINTER WEEDS, PART 2 – Winter Annual Broadleaf Weeds By Jim Brosnan, Ph.D.; Greg Breeden; and Tom Samples, Ph.D.; The University of Tennessee Photo 1. Henbit produces distinctive purple flowers each spring.
Henbit (Lamium amplexicaule)
Phenoxy herbicides
Henbit has a square stem that can be purplish in color. Branching freely from the base, henbit is characterized by its kidney-shaped, serrated leaves that can be densely hairy. Uppermost leaves lack petioles (stems that support the leaf), and the plant produces distinctive purple flowers each spring (see Photo 1).
Purple deadnettle is often confused with henbit; however, the leaves of purple deadnettle are attached to petioles, and the leaves of henbit are not. Furthermore, the leaves of purple deadnettle take on a purplish color in spring and are densely hairy (see Photo 2).
Phenoxy herbicides are the most frequently used herbicides for selective broadleaf weed control in turf. Common examples include 2,4-D, MCPP and MCPA. While such herbicides are effective individually, broadspectrum weed control is often achieved by applying products containing more than one of these materials. Multiple options are available, including Trimec Classic™ (2,4-D, MCPP and dicamba) and Three-Way™ (2,4D, MCPP and dicamba). These products are safe for use on the majority of turf species found throughout the state; however, always check the product label for specific turfgrasstolerance information.
Common chickweed (Stellaria media)
Preemergence control
Common chickweed has a shallow root system and is often found in wet, shady areas. The egg-shaped leaves are arranged opposite of one another and exhibit a shiny appearance. The lines of vertical hairs along the stem easily identify common chickweed.
In order to control any weed preemergently, control measures must be implemented prior to that weed germinating from the soil seed bank. While preemergence control for winter annual broadleaf weeds is not feasible for 2009, you may want to consider this strategy in 2010. Currently, only one commercially available herbicide can be used to provide effective preemergence control of winter annual broadleaf weeds. This product, isoxaben (marketed under the trade name Gallery 75DF), must be applied prior to weed emergence, so target applications for late summer.
Protox-inhibiting herbicides
inter annual broadleaf weeds are common problems throughout much of Tennessee. These weeds germinate from seeds in late summer and early fall, grow during the winter months and bloom the following spring.
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Identification The most important step in controlling any weed is proper identification. It is impossible to know how to control a weed without knowing what it is. A few common winter annual broadleaf weed species are outlined below. Visit http://tennesseeturfgrassweeds.org to identify other winter annual broadleaf weeds in your landscape.
Purple deadnettle (Lamium purpureum)
Postemergence control Photo 2. The densely hairy leaves of purple deadnettle take on a purplish color in spring. 16
TENNESSEE TURFGRASS
Numerous herbicides are available for postemergence control of winter annual broadleaf weeds. Listed next are the most common ones.
Carfentrazone (marketed under the trade name Quicksilver) and sulfentrazone (marketed under the trade name Dismiss) are two common protox-inhibiting herbicides used in turfgrass management. Both are safe for use on nearly all of the warm- and cool-season turfgrasses managed in Tennessee. These herbicides are most effective when applied in combination with phenoxy herbicides. Commercial products — like SpeedZone (carfentrazone, 2,4-D, MCPP and dicamba), PowerZone (carfentrazone, MCPA, MCPP and dicamba), Q4 (quinclorac, sulfentrazone, 2,4-D and dicamba) and TZone (triclopyr, sulfentrazone, 2,4-D and dicamba) — can be used to widen the spectrum of weed control provided by a single herbicide application. Some of these combination products can be especially suited
DECEMBER/JANUARY 2010 Email TTA at: tnturfgrassassn@aol.com