3/13/2017 - By Dr. Raymond Snyder

Here's a signalgrass study performed by John Cisar, Ed Nangle and Karen Williams at the University of Florida.

Tropical Signalgrass (Urochloa distachya) is a troublesome weed problem in south Florida.  During Spring – Fall 2012, we screened the use of Tribute® Total (Halosulfuron-methyl + foramsulfuron + Thiencarbazone-methyl) under different timings and at different rates and in combination with other chemicals to control Tropical signalgrass.

Materials and Methods used in this study:

1. Tribute® Total (3.2 oz./A) + methylated seed oil [MSO] (0.5% v/v) + Ammonium sulfate [AS] (1.5 lb./A)  
2. Tribute® Total (3.2 oz./A) +Sencor® (2.7 oz./A) + MSO (0.5% v/v) + AS (1.5 lb./A) 
3. Untreated control

The above Tribute combination treatments were applied to four replications of rough height bermudagrass plots with Tropical Signalgrass populations at the Falls Golf & Country Club, Lake Worth, FL, with the cooperation of Mr. Steve Pearson, CGCS.  Treated plots were not mowed or irrigated for a minimum of 24hr.  Two re-applications were made at 14 day intervals.  Plots were rated for percent weed remaining in plot over time and all data was subject to statistical analysis.

First Year Results:

We looked at a number of different scenarios for frequencies, rates and combinations.  The best results (most control) in our work came from repeat applications of Tribute (3.2 oz.) + MSO + Ammonium Sulfate with or without Sencor (2.7 oz.), when applied in the Fall with re-applications at 14 days and 28 days after the initial application (Table 1).  These treatments achieved nearly 100% control (Table 1).

These results are very encouraging and we will be expanding efforts this year to verify results and get more information especially on timing. However, it should be emphasized that this is one year’s results at one location.  And at that site on a bermudagrass rough, we observed differential control based on timings and rates.  Late spring and early summer Tribute applications, while providing reductions in Tropical Signalgrass did not result in complete control (data not provided).

This year we will look at earlier application dates, frequencies and repeat some of last year’s efforts to get more information on optimizing Tropical Signalgrass control.  Stay tuned.

Percent Tropical Signalgrass in plot over time.

Plot 10:  Pre-treatment, Tribute + MSO + AS

Plot 11: Pre-treatment, Tribute + Sencor + MSO +AS, plot 12: Untreated control

At trial end, Tropical Signalgrass eradicated from plots 10 & 11.