Purple nutsedge (Cyperus rotundus) is a problematic perennial week in turfs in Arizona and Southern California. Mon 12000 (MANAGE) and Imazaquin (IMAGE) herbicides were evaluated for post emergence control of this weed on 25 year old stands of 100% purple nutsedge at the University of Arizona. Three applications of five treatments were made on June 29, August 9, and September 17, 1993. Plots were evaluated on nine dates for percent nutsedge control. Repeat applications of Mon 12000 at either (0.062 + 0.062 + 0.062), or (0.062 + 0.031 + 0.031) lbs ai/A had control levels not statistically different from each other, although the three applications at the high rate provided slightly better control/suppression on 2 out of 9 dates only. An initial application at 0.125 lbs ai/A produced high to moderate levels of control for up to 40 DAT. A late season application at the 0.125 lb ai/A rate when preceded with no herbicide produced lower amounts of weed control in September and October. When allowed to grow without a herbicide treatment until August, the 0.125 lb ai/A rate reached a maximum of 56% control at 36 DAT. Image at 0.5 lb ai/A provided control generally equal to Mon 12000, being somewhat greater in mid season, and slightly less in September and October. Regrowth occurred in all treatments.

Post emergence control (suppression) of purple nutsedge (Cyperusrotundus) is problematic. Nutsedge produces a basal bulbil from nutlets in the early spring and continues to form adjacent bulbils until competitive effects are imposed and ground cover is established. In the last half of summer, nutlets are formed as carbohydrate sinks, which contain several growing points (tubers). These growing points provide the perennial lifestyle for these weedy species.

Mon 12000 series (active ingredient in proposed product MANAGE) was applied at different combination rates on three application dates during the summer of 1993 on solid stands of mowed purple nutsedge in order to assess efficiency as a control or suppressant agent. Imazaquin (IMAGE) was also applied at the 1x rate of 0.50 lb ai/A.

Treatments were devised as follows:
Rate lbs ai/A
1. Mon 12000 0.062 + 0.062 + 0.062
2. Mon 12000 0.062 + 0.031 + 0.031
3. Mon 12000 0.125 + nil + 0.125
4. Mon 12000 nil + 0.062 + 0.062
5. IMAGE 0.5 + 0.5 + 0.5
6. IMAGE/Mon (0.5 + 0.062) + (0.5 + 0.062) + (0.5 + 0.062)

Treatments 1-5 were repeated four times. Another observational treatment of two replicate plots was included, being treatment 6 (tank mix). Treatment 6 was not included in the statistical analysis.

Application dates were June 29, August 9 and September 17, 1993. Plots were split in half, with each experimental unit having its own (untreated) check. Plot size was 4 x 8". Treatments were applied in wind free conditions and allowed to dry for 7 hours before being hand irrigated with a rain nozzle with approximately 3/8-1/2 inch of water. A three nozzle boom using 8004 nozzles at 30 PSI provided a final delivery volume of 90 gallons per acre. Plots were mowed regularly to 3.5 inches with a rotary power mower when the canopy reached 4.0-4.25 inches. Plots were flood irrigated every 10-20 days to prevent moisture stress. Percent of the plot having live nutsedge was recorded on nine dates, and expressed as percent nutsedge control as a percent of the respective controls. The test area was fertilized once the first week in June with 1.25 lbs/1000 ft² -N- from ammonium phosphate.

Data were analyzed using the analysis of variance technique, and L.S.D. values are provided only when the herbicide effect was significant (P = 0.05 or less). All references to treatment rates are stated in lbs ai/A.

Plots were rated at 8, 22 and 40 days after treatment (DAT), from the first application made on June 29. Percent control was significant at 8, 22 and 40 DAT.

July 7, 1993 (8 DAT)

Percent control ranged from 0 to 82%, with MANAGE at 0.062 having means of 68 and 82% control. MON at 0.125 had very good control at 79%. IMAGE had 82% control as well at 8 DAT, along with MON at 0.062.

July 22, 1993 (23 DAT)

Control ranged from 0 to 89%. MON at 0.125 and 0.062 had mean purple nutsedge control of 89 and 82%, respectively. IMAGE at 0.50 lb had 67% control.

August 8, 1993 (40 DAT)

By 40 DAT, controls were diminishing and their was again, a significant treatment effect. MON at 0.125 had the highest control of 61%, followed by IMAGE (0.5) at 48%. MON at 0.062 had 32 and 18% control, respectively at this time. The second application was made on August 9.

The next three ratings were made on August 20 (52 DAT #1, 11 DAT #2), August 27 (59 DAT 31, 18 DAT #2) and September 14 (77 DAT #1, 36 DAT #2).

August 20, 1993 (52/11 DAT)

Percent control ranged from 21-59%. The repeat application of IMAGE had 59% control, followed by MON (0.062 + 0.031) at 37% while the MON (0.125 + nil) which lacked the midseason repeat treatment had 31% control. Both MON treatments which received 0.062 lbs., singly, or in repeat applications had 21% control.

August 27 (59/18 DAT)

Percent control ranged from 20 to 66%. IMAGE at the repeat 0.50 lb rate had 66% control. The best response to repeat MON treatments was realized from the (0.062 + 0.310) treatment at this time (52%), which was slightly better than the (0.062 + 0.062) MON treatment (45% control). The first application applied late season (nil + 0.062) had 30% control at 18 DAT. Decline of the high control level from the early application of without any repeat treatment (0.125 + nil) was now at 20%.

September 14, 1993 (77/36 DAT)

By 36 DAT after the second treatment, the MON (0.062 + 0.062) had 86% control, followed by IMAGE at 72% mean purple nutsedge control. The MON (0.062 + 0.031) plots had 69% control, followed by 56% control for the midseason application only of MON at 0.062 [MON (nil + 0.062)]. The first and only application of MON (0.125 + 0) had slipped to 5% control, which was essentially full recovery. A third application was made late in the season, on September 17, 1993, based on the re-appearance of purple nutsedge, regardless of treatment(s).

September 23, 1993 (86/45/6 DAT)

By the third week in September, temperatures were still warm, and the purple nutsedge was actively trying to develop nutlets via carbohydrate translocation. Control ranged from 5 to 88%.

IMAGE at the three repeat applications of 0.50 lbs each had 71% control by 6 DAT #3. MON 0.062 at three applications had 88% mean purple nutsedge control. There was no advantage by September 23 of the mid season application being either 0.062 or 0.031, as each had around 65% control for both the MON (0.062 + 0.031 + 0.031) and MON (0 + 0.062 = 0.062) treatments. Interestingly enough, the MON (0.125 + nil + 0.125) treated plots had only 5% control at 6 DAT #3. This particular treatment of the high rate late in the season had never achieved the performance of the 0.125 rate applied in late June.

October 11, 1993 (104/63/24 DAT

Percent control ranged from 30%, to 85%, with the triple application of MON at 0.062 being equal to that of MON (0.062 + 0.031 + 0.031), which had 85% mean control. The MON (nil + 0.062 + 0.062) had 77% control, being slightly less than the above treatments. IMAGE at 0.50 lbs in three applications had 77% control. The early and late season MON (0.125 + nil + 0.125) had 30% control.

October 22, 1993 (115/74/35 DAT)

The mean control ranged from 44 to 93%. MON at (0.062 + 0.031 + 0.031) had 93% control, followed by the mid season and final third application treatments on MON (nil + 0.062 + 0.062) at 81%. The three repeat applications at 0.062 had 78% control, while IMAGE at three applications of 0.5 had 73% control. The late season application of MON (0.125 + nil + 0.125) produced 45% control.

1. Purple nutsedge was suppressed and not eliminated from long term stands of Cyperus rotundus by the use of Mon 12000 and/or Image herbicides.

2. The high rate of Mon 12000 (0.062 + 0.062 + 0.062) lbs ai/A provided a maximum of 71% control at 23 DAT from the initial treatment, 86% at 36 DAT from the second application, and 85% mean control at 24 DAT from the third application in 1993.

3. By 40 DAT from the first application date, the high rate of Mon 12000 of 0.125 had 61% control. Plots treated at the initial 0.062 lb rate had 18% and 32% mean control.

4. Percent control was more variable for Mon 12000 when applied at (0.062 + 0.031 + 0.031) lbs ai/A. The mean control was usually less than the (0.062 + 0.062 + 0.062) treatment, but not significantly statistically different from the high rate treatment.

5. The initial application of Mon 12000 at 0.125 lbs ai/A had 79, 89, and 61 % control at 8, 23, and 40 DAT.

6. A second and late season application of Mon 12000 (0.125 + nil + 0.125) provided little control in September.

7. Image herbicide provided purple nutsedge control equal to that of Mon 12000 at 8 DAT, and slightly less so at 23 DAT, from the first season application only.

9. Image treated plots had slightly greater control of purple nutsedge at 11 and 18 DAT from the second applications. By 36 DAT from the second application Image had 73% mean control, and Mon 12000 at 0.062 (high rate) had 86% mean control.

10. The tank mix of Image/Mon 12000 at (0.5/0.062) lb ai/A produced high levels of control, especially after the second application date. These observations included two replications, and were not included in the statistical analysis, whatsoever.

11. The reduction in control of Mon 12000 at 40 DAT from first application may be from an immediate regrowth response from either basil bulbil lateral expansion, or from new growing points from existing nutlets.

12. Repeat applications of products and rates tested here are needed to suppress dense stands of purple nutsedge.

FN: NUTS93 O/N/D CLH

Table 1. Mean¹ percent control of purple nutsedge using Mon 12000 and IMAGE herbicides. University of Arizona, 1993.

²Percent control = % control of respective untreated check. Each experimental unit has own check plot.

³Mean of entire test on each respective date. Does not include Mon 0 + 0.062 + 0.062 on 7 July, 22 July, 8 Aug. Does not include tank mix.

⁴LSD value = Least significant difference statistic. Difference between two treatment mean must be greater than the LSD value for significant mean separation to occur.