SP642W205 TURFGRASS SCIENCE Controlling Winter Annual Broadleaf Weeds James T. Brosnan, Assistant Professor, Turfgrass Weed Science, Plant Sciences Greg Breeden, Weed Science Extension Assistant, Plant Sciences Introduction plants will produce seed in the spring that will Maintaining a vigorous turfgrass stand will protect remain in the soil until environmental against weed infestation. However, during the conditions are appropriate for germination. winter months turfgrasses are not actively growing Controlling winter annual broadleaf weeds before and are therefore susceptible to the encroachment seed set will reduce future weed problems. of winter annual broadleaf weeds. Controlling winter annual broadleaf weeds before they are able Winter Annual Broadleaf to set seed will not only reduce the likelihood of Weed Identification an outbreak the following year, but improve the Proper weed identification is an essential aesthetic quality of the turfgrass stand. step in weed control. Some winter annual broadleaf weeds commonly found in Life Cycle of Winter Tennessee turfgrasses are outlined below. Annual Broadleaf Weeds For more information on weed identification, Winter annual broadleaf weeds complete their visit http://tennesseeturfgrassweeds.org life cycle within a 12-month period. Seeds Common Chickweed (Stellaria media) germinate in the late summer and early fall; Common chickweed has a shallow root system and plants grow during the winter and flower the is often found in wet, shady turfed areas. Leaves following spring. Control measures implemented are opposite, shiny and egg-shaped to elliptic. The in the fall are often more effective than those uppermost leaves are without a petiole. Common applied in the spring once flowering has initiated. chickweed is easily identified by the lines of vertical Young, actively growing plants are more readily hairs present along the stem. Common chickweed controlled than fully mature, flowering plants. is similar to mouse-ear chickweed (Cerastium Many winter annual broadleaf weeds are vulgatum) in appearance; however, mouse-ear prolific seed producers. If not controlled, chickweed is a perennial that roots at the nodes, and has oblong leaves that are prominently hairy. Figure 1: Common Chickweed (Stellaria media) Figure 2: Corn Speedwell (Veronica arvensis) Figure 3: Henbit (Lamium amplexicaule) Figure 4: Purple Deadnettle (Lamium purpureum) Corn Speedwell (Veronica arvensis) the base of the plant. Lobes on Shepherd’s purse Corn speedwell (Figure 2) is a low-growing weed point outward. The plant is identified by the that thrives in weakened turfgrass stands. Corn heart-shaped/triangular fruit it produces in the speedwell is a common weed problem in newly spring. Shepherd’s purse is common in newly established areas of cool-season turfgrass. Like seeded turfgrass areas that lack density. other speedwells (Veronica spp.), the upper and lower leaves of corn speedwell differ in appearance Cultural Control Options and arrangement. Lower leaves are rounded, Implementing proper fertilization, mowing and toothed and arranged opposite. Upper leaves irrigation practices during the summer months are smaller, pointed and arranged alternate. The will lead to the development of a healthy, dense entire plant is covered in soft, white hairs. Corn turfgrass stand in the fall. Increasing turfgrass speedwell produces small, bright blue flowers density will reduce the number of voids in the canopy for winter annual broadleaf weeds to invade. Henbit (Lamium amplexicaule) Henbit (Figure 3) has a square stem that can be Overseeding warm-season turfgrass species like purplish. Henbit branches freely from the base bermudagrass (Cynodon spp.) with cool-season stem, the leaves are kidney-shaped, serrated and species like perennial ryegrass (Lolium perenne) densely hairy. Uppermost leaves lack petioles. can help prevent winter annual broadleaf weed Flowers are purple and arranged in whorls. problems. Overseeded perennial ryegrass will Henbit is similar in appearance to purple grow longer into the fall than bermudagrass and deadnettle (Lamium purpureum); however, the subsequently will be more competitive against uppermost leaves of purple deadnettle have a winter annual broadleaf weed invasion. red-to-purple tinge and are affixed to a petiole. Chemical Control Options Purple Deadnettle Preemergence (Lamium purpureum) Isoxaben (Gallery™ 75DF) herbicide must Purple deadnettle (Figure 4) is similar in be applied prior to the germination of weed seed, appearance to henbit (Lamium amplexicaule), so target applications for late summer. Gallery™ except that its leaves are attached to petioles, can be applied at rates of 0.66-1.33 lbs product per where the leaves of henbit are not. Leaves of acre and must be watered in after application. If purple deadnettle also often have a purplish renovating during the fall, do not apply isoxaben tinge. Purple deadnettle flowers in early spring. until seedlings have reached the three-leaf stage and are tillering. Do not use this product on warm- Shepherd’s Purse (Capsella bursa-pastoris) season turfgrasses that are to be overseeded. Shepherd’s-purse develops from a basal rosette of lanceolate, rounded leaves arranged alternately Postemergence on the stem. As the plant matures, leaves become Numerous herbicides are available for deeply lobed. Shepherd’s purse is sometimes postemergence control of winter annual broadleaf confused with common dandelion (Taraxacum weeds. While some products are discussed officinale), which has lobes that point towards below, a complete list can be found in Table 1. When applied early in the life cycle of young Sulfentrazone (Dismiss™) is a product safe for use plants, these herbicides can be highly effective. on nearly all warm- and cool-season turfgrasses grown in Tennessee. It provides control of not Auxin Herbicides only broadleaf weeds, but some grassy weeds and Auxin herbicides include 2,4-D, MCPP and MCPA. sedges as well. This product should not be applied These are the most commonly used herbicides near landscape beds nor should it be mixed or for controlling broadleaf weeds in turf. While applied near bodies of water. The label requires effective individually, broad-spectrum weed that a minimum distance of 50 feet be maintained control is often achieved by applying products to the nearest source of well water. Sulfentrazone containing more than one of these materials. (Dismiss) can be readily tank-mixed with other There are multiple options available, including herbicides to increase the spectrum of weed control. Trimec Classic™ (2,4-D, MCPP, dicamba) and Three-Way™ (2,4-D, MCPP, dicamba). Most auxin ALS herbicides herbicides are safe for use on Kentucky bluegrass Multiple ALS herbicides can be used to control (Poa pratensis), tall fescue (Festuca arundinacea), some specific winter annual broadleaf weeds. bermudagrass (Cynodon spp.) and zoysiagrass These herbicides include chlorosulfuron (Corsair™ (Zoysia spp.). Always check the product label 75WDG), metsulfuron (Blade™), rimsulfuron for specific turfgrass tolerance information. (TranXit GTA™) and trifloxysulfuron (Monument™ 75WG). Refer to each product’s label for specific These materials can injure surrounding desirable information on the species of weeds controlled. Most vegetation. Do not apply auxin herbicides of these products are only available to professional underneath or around desired vegetation or in pesticide applicators and most are not safe for conditions that favor herbicide drift or volatility (high use on cool-season turfgrass. These materials winds or temperatures greater than 85 degrees F). can also be readily tracked to non-target sites. While granular fertilizers containing auxin Non-Selective Herbicides herbicides are available, efficacy is significantly Non-selective herbicides such as glyphosate greater when these herbicides are applied as liquids. (Roundup Pro™) and diquat (Reward™ 2L) can Pyridinecarboxylic acids (or picolinic acids) be applied to dormant bermudagrass turf for Triclopyr + clopyralid (Confront™) is another control of winter annual broadleaf weeds. These option for controlling winter annual broadleaf weeds applications cannot be made to bermudagrass in Kentucky bluegrass, tall fescue, bermudagrass that are overseeded, as glyphosate and diquat and zoysiagrass; however, this product cannot will remove any overseeded perennial ryegrass be used by homeowners, nor can it be applied to or roughstalk bluegrass (Poa trivialis) present. warm-season turfgrass mowed at less than ½ inch. Conclusion Protox Herbicides The use of proper maintenance practices Carfentrazone (Quicksilver™ 1.9 EC) is a product throughout the summer will help prevent the designed to be used by professional applicators that encroachment of winter annual broadleaf weeds is safe on most warm- and cool-season turfgrasses, in the fall. Control measures should be used except hybrid bermudagrass (C. dactylon X before these weeds produce seeds that can be C. transvaalensis). Commercial products like deposited into the soil seed-bank. There are SpeedZone (carfentrazone, 2,4-D, MCPP, dicamba) multiple options for postemergence control of and PowerZone (carfentrazone, MCPA, MCPP, winter annual broadleaf weeds. Homeowners dicamba) can be used to widen the spectrum of should rely on commercially available products weed control. These combination products are containing multiple phenoxy herbicides. ideal for winter annual broadleaf control because Professional applicators can select from an the addition