Select pre and post emergence applications of Dimension herbicide, with and without the addition of MSMA were compared for weed control efficacy of Southwest cupgrass (Erichloa gracilis), a very competitive summer annual grass weed.

An initial pre-emergence application was made on March 2, 1996. Applied as a pre-emergence treatment only, Dimension at the 0.50 lb AI/A rate provided 99-100% control from initial emergence until the end of the test (August 21, 1996). Dimension as a post emergence treatment at the 0.38 lb. AI/A rate, had 85% control at 7 DAT/2, which later achieved 95% control of cupgrass. When tank mixed with 1.0 lb AI/A of MSMA, Dimension at either the 0.38 or 0.50 lb AI/A rates had essentially the same levels of control at 30, 54 and 82 DAT/2. Barricade as a pre-emergence treatment only, provided 98-100% season long control. When applied alone, MSMA (post emergence) at the 1.0 lb. AI/A rate provided 50-70% control over the season.
 
 

Southwest cupgrass (Erichloa gracilis)) is an aggressive and competitive summer annual grassy weed which is invasive in bermudagrass turf. Control is achieved by either the application of a pre-emergence herbicide, or secondly, through the application of a post emergence herbicide. Removing an emerged grassy weed in a grass (turf) crop leaves only a few herbicides options. Traditionally, MSMA is used for this purpose. A test was conducted on a golf course 25 miles south of Tucson to evaluate differential rates of Dimension herbicide, applied as post and per-emergence applications, both with and without MSMA as a post emergence test mix, for the control of Southwest cupgrass.

An area located on a golf course rough known to have a previous history of Southwest cupgrass was selected for the test. Seven herbicide treatments, as well as untreated control plots (checks) were repeated in a randomized complete block design (RCBD), featuring four replications. Plot size was 5' x 6', with both standard plot and two foot wide feet border checks included (between plots) in order to assess weed pressure accurately.

Pre-emergence treatments of Dimension at 0.5 lb. and Barricade at 0.75 lb were applied on March 2, 1996. Post emergence applications of Dimension at 0.38 lb, 0.50 lb, tank mixes of Dimension (0.38 lb/MSMA 1.0 lb), (Dimension 0.50 lb./MSMA 1.0 lb.), were applied on May 31, 1996. All rates are implied as lbs. AI/A. No cupgrass was present from March 2, until the third week of May when increased irrigation was provided to promote an otherwise nil emergence. Treatments were applied with a three nozzle boom CO₂ sprayer using three 8004 nozzle at 25 psi, applying 50 gallons per acre as the final solution rate. A full list of treatments and evaluations are listed in appendix Table -A-.

Plots were mowed two times weekly at 1.5 inches with a reel-type mower and clippings were returned to the plots. Plots were evaluated for percent cupgrass on June 7, June 29, July 24, and August 21, 1996. Weed control efficacy was determined as the ratio of the number of crabgrass plants per plot, compared to the mean of all check areas, using the formula:

Turfgrass quality, density and/or color were evaluated as applicable on the above four dates. Data was subjected to the analysis of variance technique using the GLM option of SAS software. Tukey's honest least significant difference value was calculated for treatment mean separation. Linear contrasts were used for select comparisons designed to investigate specific types of herbicide rates and pre/post emergence treatment combinations. None were statistically significant and thus are not included.

Weed control: On all four evaluation dates, the main source of variation (herbicide treatment) was significant for control of Southwest cupgrass. On June 7 (97 DAT/1: 7 DAT/2), mean weed control ranged from 48% to 100% (Table 1). Dimension at 0.50 lb/MSMA 1.0 lb had the lowest mean control (48%). The single pre-emergence application of Dimension at 0.50 lb (label 1x rate) had 100% control, followed by the pre-emergence application of Barricade (0.75 lb) at 99%, followed by Dimension 0.38 lb/MSMA 1.0 lb. post emergence at 92%. The addition of 1.0 lb of MSMA to Dimension as a post emergence treatment slightly enhanced the weed control at the low rate of (0.38 lb) verses the 0.38 lb rate of Dimension applied alone as a post emergence treatment date (92% and 85% control, respectively). On June 7, MSMA alone had better weed control than Dimension at 0.50 lb applied as a tank mixed with MSMA.

On June 29, (120 DAT/1: 30 DAT/2), weed control ranged from 78% to 99%. All treatments provided 97-99% control, with the exception of MSMA alone, which had 78% control. ( Table 1).

On July 24, (145 DAT/1: 54 DAT/2), weed control ranged from 67% to 100%. The single application of MSMA alone had 67% control. Dimension alone applied as an early post emergence treatment had 95% and 93 % control at the 0.38 lb and 0.50 lb rates, respectively. All other treatments had 100% control.

On August 21 (last evaluation), (172 DAT/1: 82 DAT/2) weed control ranged from 74% to 100% control. Again, the single application of MSMA alone (1.0 lb rate) had the lowest control of 74%. The tank mix of MSMA (1.0 lb) with either Dimension rate had 100% control material. Only two to three weeds emerged in other plots by this time (Table 1).

Turfgrass tolerance: Turfgrass response (common bermudagrass-rough) did not show differences in appearance due to the application of these treatments. The MSMA did not cause extensive damage to the turf. It should be noted that no surfactant was added to any treatments. This was true for overall turfgrass quality (June 7, 1996) and turfgrass color (July 24 and August 21, 1996).

Visual estimates of turfgrass density was significantly affected by herbicide treatment applications on June 29, 1996, using a scale of 1-9 (1 = bare turf, 9 = most dense). Mean scores ranged from 4.3 to 7.0 for the common bermudagrass treated turf (Table 2). The Dimension pre-emergence application at the 0.50 lb rate had a mean visual density score of 4.5, which was equal to that of the full size in-row check plots (4.3). The application of the Dimension 0.50 lb/MSMA 1.0 lb (tank mix) had the highest visual density mean score of 7.0. MSMA alone (post emergence) had a similar visual estimate for turfgrass density (6.0) as that of Dimension/MSMA at the 0.38 lb rate. Barricade at the 0.75 lb initial pre-emergence rate application had a mean score of 6.0 also (Table 2).

1. Control of Southwest cupgrass was achieved by either pre or early post emergence treatments of Dimension herbicide.

 
2. Applied as a pre-emergence alone, Dimension at the label 1x rate (of 0.50 lb AI/A) provided 99-100% control from the emergence period of late May until the end of August.

 
3. At (97 DAT/1: 7 DAT/2) (first evaluation date), Dimension applied alone as a post emergence treatment had 53% and 85%control, at the 0.50 lb and 0.38 lb AI/A rates, respectfully.

 
4. Applied as a post emergence with 1.0 lb AI/A of MSMA, Dimension at either the 0.50 lb AI/A or 0.38 lb AI/A rate provided essentially identical weed control on the last three evaluation dates. On the first evaluate date of June 7, the Dimension/MSMA tank mix (0.38 lb./1.0 lb. AI/A) had higher control than the same tank mix as the 0.50 lb. AI/A rate of Dimension. No biological reason for this one time observation is given.

 
5. Turfgrass color and quality was not affected by herbicide applications. Check plots were slightly lower in performance in these categories than a few of treatments.

7. No attempt was made to control more mature plants later in the season.

Appendix Table -A-. Select Pre and Post Emergence Treatments for Control of Southwest Cupgrass. University of Arizona, 1996
 

Treatment1	Rate: Lbs. AI/A	Application Type2	Date of Application
Dimension	0.50	Pre-emergence	March 2, 1996
Dimension	0.38	Post emergence	May 31, 1996
Dimension	0.50	Post emergence	May 31, 1996
Dimension/MSMA	0.38/1.00 (tank)	Post emergence	May 31, 1996
Dimension/MSMA	0.50/1.00 (tank)	Post emergence	May 31, 1996
MSMA	1.00	Post emergence	May 31, 1996
Barricade	0.75	Pre-emergence	March 2, 1996

¹Dimension active ingredient - dithiopyr MSMA. Active ingredient = monosodium methylarsinate Barricade. Active ingredient = Prodiamine.

²Pre-emergence = prior to emergence of Southwest cupgrass. Post emergence = after emergence of Southwest cupgrass. 2 tiller/3 leaf stage.

Table 1. Weed control of Southwest cupgrass after select pre and post emergence treatments applications to non-overseeded bermudagrass turf. University of Arizona, 1996.
-------------------------------------% Control ¹ ------------------------------------------

TREATMENT2	RATE AI/A3	APPLICATION4	JUNE 7 97 DAT/1:7 DAT/2	JUNE 29 120 DAT/1:30 DAT/2	JULY 24 145 DAT/1:54 DAT/2	AUGUST 21 172 DAT/1:82 DAT/2
Dimension	0.50	Pre	100	97	100	99
Barricade	0.75	Pre	99	99	100	99
Dimension	0.38	Post	85	98	95	97
Dimension	0.50	Post	53	99	93	97
Dimension  MSMA	0.38  1.00	Post  (tank)	92	98	100	99
Dimension  MSMA	0.50  1.00	Post  (tank)	48	99	100	100
MSMA	1.00	Post	82	78	67	74
Date Mean5			80	96	94	95
LSD Value6			40	12	16	12
No. weeds in all  control plots [average]			[31]	[50]	[53]	[98]

¹Percent control as percentage of weeds in control plots.

²Dimension = (dithiopyr), Barricade = (prodiamine), MSMA = (monosodium methyl arsenate).

³Are rates referred to in lbs. AI/A.

⁴Pre-emergence treatments applied March 2, 1996. Post emergence treatments applied May 31, 1996.

⁵Mean of all treated plots on each evaluation date.

⁶LSD value = least significance difference treatment mean separation statistic.

Table 2. Mean turfgrass response variables of color, quality and density on select dates after application of pre and post emergence turfgrass herbicide for the control of Southwest cupgrass on non-overseeded bermudagrass turf. University of Arizona, 1996.
---Quality ⁴ --- ---Color ⁵ --- ---Density ⁶---

TREATMENT1	RATE AI/A2	APPLICATION3	JUNE 7 97 DAT/1:7DAT/2	JUNE 29 120 DAT/1:30 DAT/2	JULY 24 145 DAT/1:54 DAT/2	AUGUST 21 172 DAT/1:82 DAT/2)	JUNE 29 120 DAT/1:30 DAT/2
Dimension	0.50	Pre	5.3	6.0	6.0	6.0	4.5
Barricade	0.75	Pre	5.5	6.0	6.5	7.0	6.0
Dimension	0.38	Post	5.5	5.5	6.0	6.8	5.0
Dimension	0.50	Post	5.3	6.5	6.8	7.0	5.5
Dimension  MSMA	0.38  1.00	Post  (tank)	6.0	6.5	6.5	6.5	6.0
Dimension  MSMA	0.50  1.00	Post  (tank)	6.0	6.3	7.0	6.3	7.0
MSMA	1.00	Post	5.8	6.5	6.3	6.8	6.0
Check	----	----	5.8	5.0	6.8	6.3	4.3
Date Mean7			5.6	6.0	6.5	6.6	5.5
LSD Value8			N.A.	N.A.	N.A.	N.A.	1.5

¹Treatment: Dimension = (dithiopyr), Barricade = (prodiamine), MSMA = (monosodium methyl arsenate).

²Are rates referred to in lbs. AI/A.

³Pre-emergence treatments applied March 2, 1996. Post emergence treatments applied May 31, 1996.

⁴Quality scores (1-9). 1 = dead grass, 9 = best possible.

⁵Color scores (1-9). 1 = dead, 9 = dark green.

⁶Density (1-9). 1 = dead, 9 = most dense.

⁷Mean of all treated plots on each evaluation date.

⁸LSD value = least significance difference treatment mean separation statistic.