Research Articles continued
Cover Story
Preemergence and Postemergence Weed Control with Specticle Virginia Tech Researchers: Jeffrey F. Derr, Ph.D., Professor of Weed Science, and Adam E. Nichols, Research Assistant, Hampton Roads Agricultural Research and Extension Center, Virginia Beach Sponsors: The Virginia Turfgrass Foundation, The Virginia Agriculture Council and Bayer
S
pecticle is the newest preemergence herbicide developed for use in bermudagrass turf. It contains the active ingredient indaziflam, which has a different mode of action — inhibition of cellulose biosynthesis — compared to other preemergence herbicides used for crabgrass control. Therefore, in addition to being an effective crabgrass preventer, Specticle also has a place in herbicide rotation programs to limit the development of resistance.
Our research
Over the past two years, we have evaluated single applications, as well as split applications, of Specticle in established stands of ‘Tifsport’, ‘Savannah’ and ‘Yukon’ bermudagrass. In our single-application trials, we covered the rate range for Specticle, from 2.5 ounces product per acre (0.031 lb. active ingredient/acre) to
5 ounces product (0.0062 lb. ai/A). We made our applications in early March for both years. In 2010 and 2011, we also compared a single application of Specticle in March at 4.4 ounces product per acre (0.05 lb. ai/A) to two applications of 2.2 ounces product per acre (0.025. lb ai/A) applied 2 months apart (March and May). Finally, we wanted to evaluate postemergence control of annual bluegrass (Poa annua), since there had been reports that Specticle could control this weed after emergence. We conducted this trial in March 2011 with well-established annual bluegrass.
Research results
In 2010, we observed excellent control with all single-applications rates in June (Table 1). When we evaluated the plots in July and September, crabgrass cover had decreased as the Specticle rate
increased. Crabgrass cover with the middle rate of Specticle was similar to that seen with Ronstar 2G, while the highest rate gave similar control as Barricade. In 2011, we observed excellent postemergence control of both Persian and corn speedwell with all singleapplication rates of Specticle (Table 2). Speedwells can be difficult to control. Even in September, preemergence crabgrass control with Specticle was excellent with all three rates in 2011. When comparing single applications to split applications, the two programs gave similar crabgrass control in 2010, while the split application tended to give better control in 2011. In our annual bluegrass trial, Specticle reduced the stand and flower production of this weed, although acceptable control was observed only at the highest rate (5 oz. product per acre), and it took over a month to
Table 1. Preemergence crabgrass control with Specticle in 2010.
SOUTHERN CRABGRASS Rate lb. ai./A
6/17/2010 % Control 84 DAT*
7/20/2010 % Cover 117 DAT *
9/2/2010 % Cover 161 DAT*
0%
51%
83%
Specticle 20WP
0.031
92%
19%
39%
Specticle 20WP
0.047
96%
12%
23%
Treatment Untreated
Specticle 20WP
0.062
98%
5%
11%
Barricade 65 WDG
0.75
99%
6%
9%
Ronstar 2G
3.0
97%
10%
19%
6
17
23
LSD (P=.05) * DAT = Days After Treatment
16 | Virginia Turfgrass Journal May/June 2012 www.vaturf.org