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Landscape and Turf Maintenance By J.T. Brosnan, G.K. Breeden, J.C. Sorochan and A.W. Thoms Preemergence Herbicide Use pring is a time for turf managers to focus on control of summer annual weeds such as crabgrass (Digitaria spp.) and goosegrass (Eleusine indica). These species complete their life cycle in one year, germinating from seed in spring, growing throughout summer, and finally setting seed in fall. If left uncontrolled, both crabgrass and goosegrass can reduce the aesthetic and functional quality of warm- and cool-season turf. Research conducted at the University of Tennessee Center for Athletic Field Safety in 2012 illustrated that high-use areas comprised of predominately crabgrass lose approximately 10 percent cover after each traffic event compared to only 1% for those containing predominantly Tifway hybrid bermudagrass (C. dactylon x C. transvaalensis). These losses in cover were associated with increases in surface hardness (measured as Gmax). An effective means for controlling summer annual weeds is the use of preemergence herbicides. A list of preemergence herbicides labeled for use on warm- and cool-season turfgrasses is presented in Table 1. S Active Ingredient Trade Name† Formulations‡,¶ Labeled Species prodiamine Barricade FL, WG Bermudagrass Seashore Paspalum Tall Fescue Kentucky Bluegrass Perennial Ryegrass dithiopyr Dimension EW, WP Bermudagrass Seashore Paspalum Tall Fescue Kentucky Bluegrass Perennial Ryegrass prodiamine + sulfentrazone Echelon SC Bermudagrass Seashore Paspalum Tall Fescue Kentucky Bluegrass Perennial Ryegrass pendimethalin Pendulum FL, G, EC Bermudagrass Seashore Paspalum Tall Fescue Kentucky Bluegrass Perennial Ryegrass pendimethalin + dimethenamid-P FreeHand G Bermudagrass Seashore Paspalum oxadiazon Ronstar G, FL, WSP Dormant Bermudagrass (FL, WSP only) Bermudagrass (G only) Seashore Paspalum (G only) Tall Fescue (G only) Kentucky Bluegrass (G only) Perennial Ryegrass (G only) Keys to success There are two keys to effectively controlling summer annual weeds with preemergence herbicides. First, be sure to apply these materials before weeds have emerged from soil (i.e., before they are visible). These herbicides do not prevent weed seed germination; rather they prevent germinated seedlings from developing into mature plants. Considering that the timeframe between germination and emergence can be quite short, it is often recommended that these herbicides be applied once soil temperatures are favorable for crabgrass seed germination. Turf managers should make their first preemergence herbicide application as soon as soil temperatures (at approximately 2 16 Landscape and Irrigation February 2013 indaziflam Specticle WSP, FL Bermudagrass † Active ingredients may be available under multiple trade names. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the University of Tennessee Institute of Agriculture. The omission of a particular trade name is not intended to reflect adversely, or to show bias against, any product or trade name not mentioned. ‡ FL = flowable; WG = water dispersible granular; EW = concentrated emulsion; WP = wettable powder; WSP = water soluble powder; SC = soluble concentrate; G = granular (not on fertilizer). ¶ Many preemergence herbicides are sold on granular fertilizer carriers. Be sure to follow label instructions to ensure that the correct rates of active ingredient and nutrients are supplied to turf when using these materials. Table 1 www.landscapeirrigation.com