Control of Mesquite-Pricklypear Complex with Aerial Application of Herbicides,

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1 Control of Mesquite-Pricklypear Complex with Aerial Application of Herbicides, SUMMARY Charles R. Hart, Extension Range Specialist, Stephenville Will Hatler, Extension Program Specialist - Stephenville Rocky Vinson, County Extension Agent Ag, Shackelford County Tommy Yeater, County Extension Agent Ag, Howard County Chase McPhaul, County Extension Agent Ag, Crockett County Hoss Sasin, County Extension Agent Ag, Callahan County 2009 Aerial application of Reclaim, Remedy, and Tordon 22K herbicides were applied at varying total spray volumes to dense stands of mesquite with an understory of pricklypear. Surmount herbicide was also compared to Tordon 22k for pricklypear control. Plots were established during the summer of 2003 in Shackelford County, summer of 2004 in Howard County, summer of 2005 in Crockett, Callahan, and Shackelford Counties, summer of 2006 in Shackelford County and summer of 2007 and 2008 in Callahan County. Final evaluations are made two years post treatment. OBJECTIVES Two of Texas most invasive and difficult to control species often occupy the same environment. Control of pricklypear in this complex has been difficult due to physical obstruction of chemical applications by mesquite foliage. Fixed-wing applications of Tordon 22K plus Remedy and Reclaim have had moderate success, with pricklypear control likely lower due to Picloram interception by mesquite foliage. Leaf interception leads to higher Picloram photodegradation and less available for control of pricklypear. Most landowners have resorted to treating mesquite first, then a separate application on pricklypear after mesquite defoliation, or treating pricklypear in late fall after mesquite leaf drop. This project was designed to look at application techniques for treating both mesquite and pricklypear with the same aerial application. MATERIALS AND METHODS Historically, helicopters have been used almost exclusively for herbicide applications in the forestry industry. The technology includes precision application with high total spray volume and large droplet size. Recently, helicopters have been used to apply Arsenal for control of saltcedar. This

2 application technology has allowed for greater plant coverage through increased canopy penetration by the high total spray volume and larger droplets. We test the use of this technology on the mesquite-pricklypear complex to allow for spray droplet penetration through the mesquite canopy resulting in increased coverage and greater control of pricklypear and mesquite with a single application. Applications were made on the Moon ranch in Shackelford County on August 6, 2003 with a rotary wing aircraft. Accuflo nozzles with a.016 orifice were used to deliver varying rates of total spray volume. This nozzle delivers an extremely large droplet size ranging from microns in size. Treatments applied in 2003 included a 16 oz/ac. rate of Crop Oil Concentrate (COC) with the herbicide in a water carrier. Applications were again made on the Morgan Ranch in Howard County on August 4, Treatments in 2004 varied in that a combination nozzle system was utilized to broaden the droplet spectrum. The spray boom was equipped with alternating Accuflo.028 and CP Nozzles. Orifices were used with each during pre-treatment tests to ensure a ratio was obtained for the two nozzles. For example, if the TSV was 10gpa, 5 gpa would be through the Accuflo nozzles and 5 gpa would be through the CP nozzles. Treatments applied in 2004 included a 32 oz/ac. rate of MSO with the herbicide in a water carrier. Similar plots were established in 2005 on August 8 in Shackelford County, August 3 in Crockett County, and August 7 in Callahan County. The same combination nozzle configuration was again used in Treatments applied in 2005 also contained a comparison between methylated seed oil, non-ionic surfactant and diesel as adjuvants. During 2006 treatments were applied on July 17 on the Davis Ranch in Shackelford County and included varying combinations of Reclaim, Remedy, Tordon and Surmount. During 2007, three replicated treatments were made on the Shaw Ranch property in Callahan County on August 8. These treatments evaluated CP and Accuflo nozzles individually compared to the combination setup during an early August application window. The same treatments were repeated on June 30, 2008 on the Williams Ranch in Callahan County. Both Tordon 22K and Surmount herbicides were evaluated for pricklypear control. The standard commercial rates of Reclaim and Remedy herbicides were simultaneously applied for mesquite control. Herbicide rates and total spray volumes are summarized in Table 1. The helicopter was equipped with a GPS system for precise calculation of acres and areas sprayed. Figures 1-7 show the layouts of the various treatments at each site. Plot sizes were 10 acres for all plots except the 2003 Surmount tests. Evaluations will be made at one and two years post treatment to determine percent mortality of pricklypear and mesquite. Evaluations are made by three observers walking through each plot counting 100 plants as live or dead. Initial pricklypear

3 mortality is estimated as percent desiccation. Final mortality evaluations are made two years post-treatment. Table 1. Herbicide combinations, rates, and total spray volumes applied on mesquitepricklypear complex in 2003 through Herbicide Rates Total Spray Vol. Plot Size 2003 (a.i./acre) (gallons) (acres) Tor+Rec+Rem+COC lbs Tor+Rec+Rem+COC lbs Tor+Rec+Rem+COC lbs Sur+Rec+Rem+COC lbs. 4.1 Sur+Rec+COC lbs Tor+Rec+Rem+MSO lbs Tor+Rec+Rem+MSO lbs Tor+Rec+Rem+MSO lbs Sur+Rec+Rem+MSO lbs Tor+Rec+Rem+MSO lbs Sur+Rec+Rem+MSO lbs Tor+Rec+Rem+MSO lbs Sur+Rec+Rem+MSO lbs Sur+Rec+Rem+NIS lbs Sur+Rec+Rem+Diesel lbs Tor+Rec+MSO lbs Sur+Rec+MSO lbs Sur+Rec+NIS lbs Sur+Rec+Diesel lbs Tor+Rec+Rem+NIS lbs Sur+Rec+Rem+NIS lbs Tor+Rec+NIS lbs Sur+Rec+NIS lbs Sur+Rec+Rem+NIS lbs Sur+Rec+NIS lbs Sur+Rec+Rem+MSO lbs. 20 w/cp 10 Sur+Rec+Rem+MSO lbs. 20 w/cp+accuflo 10 Sur+Rec+Rem+MSO lbs. 20 w/accuflo Sur+Rec+Rem+MSO lbs. 15 w/cp 20 Sur+Rec+Rem+MSO lbs. 15 w/cp+accuflo 20 Sur+Rec+Rem+MSO lbs. 15 w/accuflo 20 Sur=Surmount, Tor=Tordon 22K, Rec=Reclaim, Rem=Remedy herbicides. MSO=Methylated Seed Oil, NIS=Non-ionic Surfactant, COC=Crop oil concentrate. Emulsifier was used with Diesel treatments.

4 Figure 1. Layout of aerial plots on the Moon Ranch in Shackelford County applied on August 6, 2003.

5 Figure 2. Layout of aerial plots on the Morgan Ranch in Howard County applied on August 4, 2004.

6 Figure 3. Layout of aerial plots on the Chandler Ranch in Crockett County applied on August 3, 2005.

7 Figure 4. Layout of aerial plots on the Finley Ranch in Callahan County applied on August 7, 2005.

8 Figure 5. Layout of aerial plots on the Mathews Ranch in Shackelford County applied on August 8, 2005.

9 Figure 6. Layout of aerial plots on the Davis Ranch in Shackelford County applied on July 17, 2006.

10 Figure 7. Layout of aerial plots on the Shaw Ranch in Callahan County applied on August 8, 2007.

11 Figure 8. Layout of aerial plots on the Williams Ranch in Callahan County applied on June 30, 2008.

12 RESULTS AND DISCUSSION Shackelford County 2003 Site Final results from treatments applied on the Moon Ranch in Shackelford County are presented in Table 2. With the larger droplet size, mesquite mortality was not acceptable. Pricklypear mortality was good, averaging % mortality with Tordon 22K across all spray volumes. Surmount provided slightly lower mortality compared to Tordon 22K when compared at similar spray volumes. Results of this research indicate 1) the rate of Surmount should be increased to 4 pints/acre, and 2) large droplets do a good job penetrating through the mesquite canopy and controlling pricklypear, but no mesquite mortality was realized. Table 2. Final results (2 years after treatment) of treatments applied to mesquite and pricklypear on the Moon Ranch in Shackelford County in Applications made by helicopter with.016 Accuflo nozzles. Herbicide Combinations Rates TSV Pricklypear Mesquite (gal.) (% Apparent Mortality) Tordon 22K+Reclaim+Remedy lbs Tordon 22K+Reclaim+Remedy lbs Tordon 22K+Reclaim+Remedy lbs Surmount+Reclaim+Remedy 3 pts lbs Surmount+Reclaim 3 pts+0.25 lbs Sur=Surmount, Tor=Tordon 22K, Rec=Reclaim, Rem=Remedy herbicides. Howard County 2004 Site Final results from treatments applied in 2004 are presented in Table 3 and Figure 9. Initial results indicate that Surmount provided faster desiccation on pricklypear cactus compared to Tordon 22K at similar spray volumes. Percent desiccation of pricklypear increased with increases in total spray volumes. The 2004 treatments yielded valuable information regarding total spray volume, revealing that 10 gpa is too low and volumes above 20 gpa are unnecessary. Table 3. Final results (2 years after treatment) of treatments applied to mesquite, pricklypear and redberry juniper in Herbicides Rates TSV Pricklypear Mesquite Juniper (gal.) (% Desiccation) (% Mortality) (% Mortality) 1.Tor+Rec+Rem lbs Tor+Rec+Rem lbs Tor+Rec+Rem lbs Sur+Rec+Rem 3 pts lbs Tor+Rec+Rem lbs Sur+Rec+Rem 3 pts lbs Sur=Surmount, Tor=Tordon 22K, Rec=Reclaim, Rem=Remedy herbicides.

13 % Mesquite Mortality 100.0% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% Treatment No. 100% % Pricklypear Desiccation 80% 60% 40% 20% 0% Treatment No. Figure 9. Percent mesquite mortality and percent pricklypear desiccation two years after aerial treatments applied on the Morgan Ranch in Howard County during 2004.

14 Callahan, Shackelford and Crockett Counties 2005 Two year results from treatments applied in 2005 are summarized in Table 4 and presented by site in Figure 10. There were site differences evident among the three sites with the Shackelford County (Mathews) site resulting in significantly lower mesquite and pricklypear mortality. We attribute this to lower soil temperatures (<75F) at the time of spraying due to high moisture conditions following heavy rains. Initial results one year after treatment indicated that Surmount provided faster desiccation on pricklypear cactus compared to Tordon 22K at similar spray volumes. However, no differences were evident following two year evaluations (Figure 11). Results did show a slight decrease in both mesquite and pricklypear control when Remedy was not included in the mix. Additional evaluations were made comparing Methylated Seed Oil (MSO), Non-Ionic surfactant (NIS) and Diesel:Water emulsion in the mix. Results show no differences among adjuvant for mesquite or pricklypear control two years after treatment. Table 4. Final results (2 years after treatment) of treatments applied to mesquite and pricklypear averaged across three sites in Herbicides Rates TSV Pricklypear Mesquite (gal.) (% Mortality) (% Mortality) Tor+Rec+Rem+MSO lbs ± ±6.8 Sur+Rec+Rem+MSO lbs ± ±9.9 Sur+Rec+Rem+NIS lbs ± ±3.1 Sur+Rec+Rem+Dies lbs ± ±15.9 Tor+Rec+MSO lbs ± ±18.6 Sur+Rec+MSO lbs ± ±17.4 Sur+Rec+NIS lbs ± ±13.2 Sur+Rec+Dies lbs ± ±13.2 Sur=Surmount, Tor=Tordon 22K, Rec=Reclaim, Rem=Remedy herbicides. Figure 10. Apparent mesquite and pricklypear mortality by site two years after treatments in 2005.

15 Figure 11. Apparent mesquite and pricklypear mortality with and without Remedy in the mix and with Tordon compared to Surmount two years after treatments in 2005.

16 Shackelford County Site 2006 Final results for this site are presented in Table 5 and Figures Mesquite mortality did not improve from year one to year two after treatment, remaining lower than expected. Interestingly, the highest mesquite mortality occurred on plots receiving the lowest total spray volume. The lack of consistency and low mortality indicates that soil temperatures were too low and conditions were not ideal for mesquite herbicide application at the time these plots were installed Pricklypear mortality increased dramatically in the second year after treatment. All treatments were successful, however, the plot sprayed with a combination of Surmount, Reclaim, and Remedy at 20 gpa showed the best results. Table 5. Final results (2 years after treatment) of treatments applied to mesquite and pricklypear on the Davis Ranch in Shackelford County in Herbicides Rates TSV Pricklypear Mesquite (gal.) (% Desiccation) (% Mortality) Tor+Rec+Rem+NIS lbs Sur+Rec+Rem+NIS lbs Tor+Rec+NIS lbs Sur+Rec+NIS lbs Sur+Rec+Rem+NIS lbs Sur+Rec+NIS lbs Sur=Surmount, Tor=Tordon 22K, Rec=Reclaim, Rem=Remedy herbicides. Percent Apparent Mortality of Mesquite 2 Years After 2006 Treatments % Mesquite Mortality Treatment No. Figure 12. Percent apparent mesquite mortality two years after aerial treatments applied on the Davis Ranch in Shackelford County during 2006.

17 Percent Apparent Dessication of Pricklypear 2 Years After 2006 Treatments % Pricklypear Dessication Treatment No. Figure 13. Percent apparent pricklypear desiccation two years after aerial treatments applied on the Davis Ranch in Shackelford County during Callahan County Site 2007 Final results for treatments applied in 2007 are presented in Table 6 and Figures Although excellent results were noted in all pricklypear treatments, the highest mortality was achieved in plots sprayed with CP nozzles alone. Extremely wet conditions in 2007 led to poor mesquite control and excellent pricklypear control. Other commercial mesquite treatments applied the same year also showed lower mortality. Table 6. Final results (2 years after treatment) of treatments applied to mesquite and pricklypear on the Shaw Ranch in Callahan County in Herbicides Rates Nozzle TSV Pricklypear Mesquite (gal.) (% Mortality) (% Mortality) Sur+Rec+Rem+MSO lbs. CP Sur+Rec+Rem+MSO lbs. CP+Accuflo Sur+Rec+Rem+MSO lbs. Accuflo Sur=Surmount, Rec=Reclaim, Rem=Remedy herbicides.

18 Percent Apparent Mortality of Mesquite 2 Years After 2007 Treatments % Mesquite Mortality Treatment No. Figure 14. Percent apparent mesquite mortality two years after aerial treatments applied on the Shaw Ranch in Callahan County during Percent Apparent Mortality of Pricklypear 2 Years After 2007 Treatments % Pricklypear Mortality Treatment No. Figure 15. Percent apparent mortality of pricklypear two years after aerial treatments applied on the Shaw Ranch in Callahan County during Callahan County Site 2008 Initial results for treatments applied in 2008 are presented in Table 7. Apparent desiccation of pricklypear at one year after treatment was highest in treatments applied with CP and Accuflo

19 nozzles individually. Mesquite initial mortality was highest in the treatment applied with Accuflo nozzles. Table 7. Initial results (1 year after treatment) of treatments applied to mesquite and pricklypear on the Shaw Ranch in Callahan County in Herbicides Rates Nozzle TSV Pricklypear Mesquite (gal.) (% Desiccation) (% Mortality) Sur+Rec+Rem+MSO lbs. CP Sur+Rec+Rem+MSO lbs. CP+Accuflo Sur+Rec+Rem+MSO lbs. Accuflo Sur=Surmount, Rec=Reclaim, Rem=Remedy herbicides. ACKNOWLEDGMENTS This project was supported by Dow AgroSciences, North Star Helicopters, Shackelford County, Callahan County, Crockett County, Howard County, and cooperating ranches. The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.