Academic Programs

 Certificate Program

 Classes by Phil Busey

 Degree Requirements

 Golf and Sports Turf

 Grass Biology

 Landscape IPM

 Living Lawn

 Turfgrass Culture

 Research Interests

 Weed Science

Weed Science

Torpedograss Control

Some of the research summarized in this preliminary report was subsequently published in the scientific paper, "Reduction of torpedograss (Panicum repens) canopy and rhizomes by quinclorac split applications".

Drive 75 DF by BASF received a conditional pesticide registration in Florida on 1 July 1999.  The Florida Department of Agriculture and Consumer Services approved the Drive registration based on an earlier EPA-approved label for use in selected turfgrasses including bermudagrass.  The active ingredient, quinclorac, has been used under the label Facet in rice.

Florida golf course superintendents have long awaited the availability of this product for control or suppression of torpedograss, Panicum repens.  Torpedograss is a serious weed in bermudagrass turf, and no other product has been shown to provide selective control of torpedograss in turf.  Research documenting the effectiveness of quinclorac for selective control of torpedograss in bermudagrass turf was done by Drs. Lambert B. McCarty, Jeffrey M. Higgins, and Daniel L. Colville (1993.   Weed Technology 7:911-915).

The figure shows percent torpedograss, average of six replicates, in plots at Sabal Palm Golf Course.  Drive treatments are labeled based on pounds active ingredient per acre.  So where the graph says Drive 1.5 this means actually 2.0 pounds Drive 75 DF per acre.  Plots were sprayed with individual products or tank mixtures from a hand-held spray boom, using a CO2 backpack unit delivering 48 psi near the nozzles.   The experimental design was randomized complete block, with six replications of plots 4 feet x 8 feet.  For statistical analysis, Drive treatments and Illoxan treatments were analyzed as factors. Vertical white regions highlight the time spans of a first and second round of up to three treatments, superimposed on the same plots.  The chronology started with a "Before treatment" evaluation on 15 Nov 1998, then plots were sprayed with Drive and/or Illoxan on 21 Nov 1998.  The first round of treatments (21 Nov 98, 13 Dec 98, and 02 Jan 1999) involved three split applications of Drive (0.5 pounds ai/Acre x 3) or a single application of Drive (1.5 pounds AI/Acre) on the middle date, 13 DEC 98.  The Illoxan treatments (including tank-mixtures with Drive) were applied at 1 oz/1000 sq ft on 21 Nov 98 and at 0.5 oz/1000 sq ft on 13 DEC 98.  The second round of treatments (21 Apr 99, 12 May 99, and 02 Jun 99) followed the same pattern as in the first round.

We have have been doing extensive research with Drive 75 DF, starting when we received the product from BASF, August 1998.  One of our concerns was whether the labeled rates would be effective.  Dr. McCarty's research showed, "Quinclorac applied at 2.2 kg/ha followed by 1.1 kg/ha applied 3 or 6 wk after the initial controlled torpedograss best with least reduction in bermudagrass quality."  Yet the label says, "Do not apply more than 2 pounds of Drive 75 DF herbicide per acre (or 0.73 ounces per 1,000 square feet) in one year."  What control of torpedograss would result at the label rate, only 50% of the annual rate used in the earlier study?

The short answer is, "Good to excellent control under some circumstances, but not eradication."  We base this preliminary interpretation on lengthy trials at Jacaranda Country Club and Sabal Palm Golf Course, both in Broward County, Florida, and numerous smaller tests, such as grass tennis courts at the Lipton in Key Biscayne.   The Drive label says, "do not apply to golf course collars and greens," so we wanted to see what would happen to close-cut bermudagrass, hence the use of the Lipton.  Despite temporary discoloration of hybrid bermudagrass, we found that at the label rate (split into 5 applications) there was no lasting injury to the close-cut bermudagrass turf, and there was 100% control of torpedograss at the Lipton.   Elsewhere in higher cut bermudagrass, there was at best 90% control, for example, Sabal Palm Golf Course, and less control of torpedograss at Jacaranda Country Club.

Environmental conditions and application method at Jacaranda and Sabal Palm differed, which may explain why torpedograss control was very noticeable at Sabal Palm, but temporary at Jacaranda.  The Jacaranda site is very moist, consisting of an impounded level area receiving considerable water drain off from an adjacent tee and nursery green.   Sabal Palm is a dry site.  Both sites are out of play, for example, the Sabal Palm site is essentially a rough type area between the first green and the second tee.   Both sites appear to have hybrid bermudagrass, except torpedograss was the main vegetation component, 60-70% of the canopy at Sabal Palm and 90-95% at Jacaranda.   Methylated seed oil (MSO) was used as an adjuvant at Sabal Palm, but was used at Jacaranda only in the last set of treatments.

Visual evaluations of percent torpedograss had an average 67% before treatment (average of all plots), and 63% after treatment (average of untreated controls during multiple evaluations over 234 days), and 64.8% on the last four evaluation dates.  In contrast, Drive treated plots had 6.3% and 11.4% torpedograss, for the 0.5 x 3 apps versus 1.5 x 1 app treatments, respectively.  This represents 90% control, in the case of the 0.5 pound x 3 applications treatment.

Analysis of variance and orthogonal contrasts showed that overall (based on "After" mean of all dates) Drive was very highly effective (P << 0.01) in reducing torpedograss, and that split applications were much more effective (P << 0.01) than single applications, at the same cumulative rate.  Illoxan had no overall effect (P=0.09), although it had a significant (P < 0.05) positive effect on two dates of evaluation.   The interaction of Drive and Illoxan had no overall effect (P=0.07) although it had a significant effect on two dates of evaluation.

Suppression of torpedograss from only a single round of treatments was not adequately effective, in our estimation, to be practical value at the Sabal Palm site.  Torpedograss had already begun its recovery by 02 April 1999, just before the second round of treatments.  While the plots were small, only 4 feet wide, and one would expect border effects and reinvasion from neighboring plots, this seem to be a plausible factor during the relatively short term (two months) that torpedograss appeared to recover.  It is likely that torpedograss reappearance was due to buried rhizomes which had escaped treatment. 

Conclusions

Based on this research as well as observations at Broken Sound Golf Course in Palm Beach County Florida (our observations of earlier plot research by BASF), it appears that effective control of torpedograss in bermudagrass turf can occur from repeated small doses of Drive 75 DF.  There is no advantage, in fact a disadvantage, in allocating the entire labeled 2.0 pounds per acre per year (1.5 pounds active) in a single application.  Repeated yearly applications also seem necessary to get a high degree of control.  Tank mixtures with Illoxan initially showed an advantage, but over time did not appear to provide an advantage.