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HERBICIDE PRE-MIXES SIMPLIFY WEED CONTROL By Hunter Perry and Scott McElroy, Ph.D., Department of Agronomy and Soils, Auburn University
Alabama Turf Times >>> Fa l l 20 10
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ntil now, turfgrass managers have had few herbicide options that provide a broad spectrum of broadleaf and grass weed control while maintaining turf safety. Celsius速 herbicide is a new three-way mixture of thiencarbazone-methyl, iodosulfuron and dicamba for postemergent control of broadleaves and some grasses. Approximately 150 broadleaf and grassy weeds are reportedly controlled with this product. Dicamba is commonly found in many existing premixtures, such as Trimec速, Speedzone速 and their many varieties. However, thiencarbazone and iodosulfuron are both new active ingredients to the turfgrass arena. Iodosulfuron has previously been utilized in rice and cereal crops for broadleaf control, while thiencarbazone has provided a broad spectrum of broadleaf and grass control in corn. These two new actives provide turfgrass managers a new tool for managing resistance to some post-emergent herbicides. Celsius typically promotes symptom expression and death to weeds in one to four weeks, which is slightly slower than many 2,4-D containing products. Golf course superintendents are not the only beneficiaries of this new product. The excellent safety to St. Augustine, centipede, bermuda and zoysia will allow lawncare operators to apply Celsius to mixed stands of turf without fear of phytotoxicity. Use rates range from 2.5 to 5.0 oz./acre, depending on the intended use. Other niches of Celsius include activity on Virginia buttonweed, dallisgrass and crabgrass. The higher use rate (5.0 oz./acre) is recommended for these species. The Celsius label recommends a tank-mix with Revolver速 in late-summer to early fall for enhanced dallisgrass activity. As with many existing herbicides, repeat applications may be necessary for complete control of dallisgrass and Virginia buttonweed. Crabgrass control is another perk, but better control is achieved when applied to earlier life stages. Celsius also provides a window of extended weed control due to the pre-emergent nature of the active ingredients. Soil activity extends to approximately 60 days following application. One study at Auburn University evaluated pre- and early post-emergent control of crabgrass with Celsius. The greatest control was achieved with repeat applications of Celsius at 3.7 oz./acre (one application PRE and the other early POST). Crabgrass control was 85% 17 weeks after initial application (WAIA). Other studies at Auburn University have evaluated Celsius at various rates to determine how it compares with industry standards for broadleaf weed control. The first study was conducted on a mixed stand of bermudagrass and centipede to evaluate common lespedeza
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control (common lespedeza, or Japanese clover, is a mat-forming, broadleaf weed that is commonly confused with black medic). Trimec Classic and atrazine provided the quickest control, but Celsius at 5.0 oz./acre controlled the lespedeza 100% at 4 WAIA (see Figure 1). The 3.7 oz./A rate of Celsius controlled lespedeza 63% 4 WAIA, but 86% control resulted following the sequential application. These results indicate that the higher rate of Celsius may be needed for complete control of common lespedeza. No injury was observed on either turfgrass species following Celsius application. Another study evaluated Celsius for the control of henbit and wild violet. Atrazine (1 qt./A) again provided the quickest control for both weed species; however, Celsius was comparable at 10 WAIA. All herbicides controlled henbit 100%. Celsius applied sequentially at 3.7 oz./A provided 100% wild violet control. The broad spectrum of weeds controlled, coupled with turfgrass safety, makes Celsius a beneficial herbicide. Also, the weed control window provided by the POST and PRE activity may allow turfgrass managers to make fewer herbicide applications. Celsius is a new herbicide, however, and we are just beginning to understand how to most effectively use it. Is it truly better and more cost effective than standard products like Trimec or atrazine? Only time will tell.