Final Report

U.S. Environmental Protection Agency Grant

Project Name: Control of Giant Cane in Riparian and Wetland Areas of

Northern and Central California

You may also download a copy of this report as a WordPerfect file from DFG-EPAreport.doc

GENERAL INFORMATION

This grant became effective October 1, 1997. This project has three primary objectives: (1) to determine the best methods for giant cane control in northern and central California; (2) to educate the public regarding the giant cane threat; and (3) to gather information regarding giant cane’s current presence in northern and central California and its potential for further invasive spread in the region. These objectives were accomplished via the following four tasks:

1) the establishment of a giant cane control demonstration project; 2) the completion of an herbicide risk assessment for nontarget aquatic species; 3) the development of giant cane educational materials; and 4) the completion of a giant cane survey project for northern and central California.

REPORTS BY TASK

Task 1: Demonstration Project

The objective of this task was to assess the relative efficacy of the three herbicide application methods most commonly used for giant cane control. Each of these methods involved the use of Rodeo®, a commercially available herbicide which contains 53.8% of the active ingredient glyphosate. Two of the methods also involved the use of R-11®, a commercially available non-ionic surfactant which contains 90% alkylphenol ethoxylates.

The project was located at Gray Lodge Wildlife Area (GLWLA) in Butte County. Giant cane at GLWLA occurs in discrete stands in seasonal wetland sites and along permanent waterways. The three herbicide application methods tested at the GLWLA sites were:

    1. Cut Stump: Rodeo® was applied at 100% strength with a paint brush within one to two minutes after stem cutting. The entire cut portion of the stem was treated and marked with a dye to ensure adequate coverage. Stem cutting and herbicide applications occurred in October 1998.
    2. Cut-Grow-Spray: Giant cane stems were cut with chainsaws three to six weeks before foliar applications of Rodeo® at 2% and R-11® at 0.5%. The cane stems had regrown to a height of approximately six to eight feet by the time of the herbicide applications in September 1998. The herbicide applications were made by helicopter.
    3. No Cut: Aerial applications of Rodeo® at 2% and R-11® at 0.5% were made to uncut giant cane stands by helicopter in September 1998. This was approximately three weeks prior to the initiation of giant cane flowering at GLWLA.

Giant cane density and other, associated data were recorded for randomly selected 1-m2 test quadrats located along plot transects. Each herbicide application method was tested in triplicate to reduce variability within test plots of the same application group. Measurements were taken prior to herbicide application and at 60, 270, 340 (or 360) days after treatment (DAT).

Giant Cane Control - While each method provided some degree of control, the cut-grow-spray plots had the largest decrease in giant cane stem density at 82.%. The cut stump method provided a mean decrease of 76% and the no cut method provided 33% control. In comparison, the untreated control plots experienced a mean increase in giant cane stem density of 21.%.

Resprouting in Slash Piles - Giant cane stems from cut stump and cut-grow-spray plots were stacked in slash piles immediately after cutting. Slash piles were located adjacent to the test plots, but away from surface water. Monitoring was conducted on a monthly basis up to 360 DAT to monitor stem resprouting. No resprouting was observed in any of the slash piles during the project period. At 360 DAT, all stems were highly desiccated with no evidence of living tissue.

Recolonization by Other Species - Very little recolonization by other plant species was observed in the test plots during the project period. Among the few species that were observed were: cattail Scirpus sp; saltgrass Distichlis spicata; rabbits-foot grass Polypogon monospeliensis; and field bindweed Convolvulus avensis. While these species were observed colonizing the test plots after giant cane removal, they were not present in any notable density.

Herbicide Damage to Non-target Vegetation - Observations of the health and vigor of non-target plants in close proximity to the test plots did not reveal appreciable herbicide-caused impacts, even in test plots where aerial herbicide applications had been conducted. Some herbicide-induced chlorosis was observed on some adjacent willows Salix sp. a few weeks after treatment, but the trees appeared unaffected by the herbicide applications by the following spring.

Discussion

The results of this study indicate that herbicide efficacy on cut stems is superior to uncut stems, however. Acceptance of this conclusion, however, requires the consideration of several important factors including herbicide application timing, target foliage canopy and foliar characteristics, and herbicide application rates. With regards to herbicide application timing, several researchers have suggested that glyphosate applications to uncut stems are more efficacious when made at, or just after, giant cane flowering (Bell 1997; Omori 1996). Applications of systemic herbicides during this stage are believed to be more effective because of the post-flowering movement of photosynthates and other assimilates away from the growing points to root storage structures. Aerial herbicide applications occurred approximately three weeks prior to the initiation of giant cane flowering at GLWLA. Aerial applications could not have been conducted later in the season because the large numbers of migrating waterfowl that arrive at the wildlife area in early fall pose a significant collision hazard to aircraft. Because of this, herbicide applications made to the no cut plots may have been less efficacious than they would have been had they been made closer to the flowering stage for giant cane.

Foliar and canopy characteristics also have an influence on herbicide uptake and efficacy (Bussan and Dyer 1999). This is exemplified by the differences in control efficacy in the cut-grow-spray and no cut test plots. Aerial herbicide applications were made to both types of test plots using the same application rate. Nevertheless, the cut-grow-spray plots exhibited a much greater degree of giant cane control compared to the no cut plots (82% vs 33.%). A possible explanation for this difference may be found in the differences in the canopy and foliar characteristics of the two test plot methods. The no cut plots were tremendously overgrown with very little space between individual canes. Further, the heavy foliar growth of many individual canes caused a lodging effect that may have shielded lower stems from the herbicide spray. Finally, the no cut plots had large amounts of older, necrotic foliage that could have resisted herbicide uptake. In contrast, the cut-grow-spray canopy was comprised of young (8 weeks) regrowth. This regrowth was not as dense as the foliage in the no cut plots. Further, the canes had an overwhelmingly upright growth characteristic with significant space between individual canes. Finally, the foliar tissue was uniformly green and actively growing which may have facilitated herbicide uptake.

With regards to herbicide application rates, the GLWLA study used a tankmix containing 2% Rodeo® and 0.5% R-11® in water for the no cut and cut-grow-spray plots. The 2% rate was based on the specific recommendation for giant cane control provided by the Rodeo® product label. While not specifically recommended for giant cane control, the Rodeo® product label allows up to an 8% tankmix solution of the herbicide, depending on the equipment being used. Taking this into account, it may be possible to achieve a greater level of control using a higher concentration, especially with no cut applications.

Management Implications

The results of this study indicate that giant cane control with glyphosate herbicides is best achieved in conjunction with stem cutting. Both the cut-grow-spray and cut stump methods provided higher levels of giant cane control as compared to the no cut method (82% and 76%, respectively vs 33%). Acceptance of these results, however, needs to be tempered by several important factors including the influence of herbicide application rates and herbicide application timing relative to giant cane flowering.

Perhaps the most important observation gained from this study is the influence of canopy and foliar characteristics on herbicide deposition and uptake. The low biomass, young foliage of the cut-grow-spray plots appeared to provide an ideal target for herbicide deposition and uptake compared to the rank, older growth of the no cut plots.

Because the scope of this study did not extend past 360 DAT observations, it would be unwise to interpret the results as advocating single herbicide applications without follow-up. Giant cane is a difficult species to control. Its successful eradication from any site, regardless of the control method employed, requires diligence in post-treatment monitoring and re-application of herbicides to regrowth. Additionally, it is important to acknowledge that the decision to select one control method over another is often influenced by site specific conditions. For example, aerial application may not be suitable due to the proximity of trees, powerlines or high-use roads. Conversely, projects that involve stem-cutting, may not be time or cost efficient for large giant cane stands. In these types of situations, the no-cut method used in conjunction with intensive post-treatment follow-up may be preferable.

Literature Cited

Bell, G.P. 1997. Ecology and management of Arundo donax and approaches to riparian habitat restoration in southern California. In: Plant Invasions: Studies for North America and Europe on the ecology and management of alien plants. J.H. Brock, M. Wade, P. Pysek and D. Green (eds.). Backhuys Publishers, Leiden, The Netherlands. 114- 126.

Bussan, A.J., and Dyer, W.E. 1999. Herbicides and rangeland. In: Biology and management of noxious rangeland weeds. Shelly, R.L., and Petroff, J.K. (eds.). Oregon State University Press, Corvallis, Oregon. 116-132.

Omori, G. 1996. Eradicating the giant reed (Arundo donax) in riparian areas of Marine Corps Base, Camp Pendelton, CA. Agri Chemical and Supply Inc., Oceanside, CA. 19 pp.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Task 2: Hazard Evaluation

The second objective of this study was to assess the impacts of the use of glyphosate and a alkylphenol ethoxylate surfactant on non-target aquatic fauna. In the past two decades, researchers have noted a general decline in amphibian species worldwide. Pesticide use has been suggested as one possible factor for this phenomenon. Laboratory toxicity tests conducted with amphibians and formulations of glyphosate, however, have been limited. One study by Bidwell and Gorrie (1995) found that the glyphosate herbicide Roundup® 360 and technical grade glyphosate had different toxicities to two species of Australian frogs, Crinia insignifera and Litoria moorei. Results showed that adult C. insignefera were more susceptible to Roundup® 360 (96-h LC50 of 39.7 mg.L) than glyphosate technical (96-h LC50 of 78.0 mg/L). The authors believed that the surfactant in Roundup® 360 caused the increased toxicity. The study also determined that Roundup® 360 and technical glyphosate were both found to be more toxic to tadpoles of L. moorei, than the adult life stage.

Two amphibian species, the foothill yellow-legged frog Rana boylii and the California red-legged frog Rana aurora draytonii occupy riparian areas of northern and central California. R. boylii is a California species of special concern while R. aurora draytonii is a federally listed threatened species (California Department of Fish and Game 1994). Both species may be present in areas selected for giant cane control projects, however, no specific data regarding the hazard of herbicide applications to these species is currently available. To address this issue, the California Department of Fish and Game (DFG) investigated the toxicological impacts of glyphosate herbicide (Rodeo®) and an alkylphenol ethoxylate surfactant (R-11®) on larval fathead minnows Pimephales promelas, and larval southern leopard frogs Rana pipiens. Water samples for chemical residue analysis and acute toxicity testing where collected from waterways directly adjacent to the herbicide/surfactant applications. Additionally, the acute toxicities of Rodeo® and a Rodeo®/ R-11® tankmix were determined in the laboratory for the fish and frog species in 96-h toxicity tests (CDFG 1998).

LC50 Determinations and Field Concentrations

The 96- h LC50 values for glyphosate for larval Rana frogs and fathead minnows were found to be >1,211 mg/L and 1,240 mg/L, respectively (Table 1). Water samples collected from adjacent waterways one hour after aerial herbicide applications contained glyphosate concentrations ranging from 0.057 to 0.155 mg/L. When compared, the laboratory-determined LC50 value and the herbicide concentrations in water indicate a 10,000-fold margin of safety for larval fish and frogs when glyphosate is applied by air to control giant cane.

The 96- h LC50 for the surfactant R-11® for bluegill sunfish Lepomis macrochirus (Monsanto 1983a) and rainbow trout Oncorynchus mykiss (Monsanto 1983b) is approximately 4.0 mg/L. Water samples collected one hour after the herbicide/surfactant application contained a maximum surfactant concentration of 0.013 mg/L. When compared, the laboratory-determined LC50 value and the surfactant concentrations in water indicate a minimum100-fold margin of safety for fish when the surfactant is applied directly to water.

Table 1. Comparison of herbicide and surfactant aquatic toxicity values and measured field concentrations for larval fish and frogs.

Compound

96-h LC50

fish (mg/L)

96-h LC50

frog (mg/L)

Field Conc

(mg/L)

Margin of Safety

Rodeo®

1,240

>1,211

0.155

10,000-folda

R-11®

4.0b

****

0.013

100-foldc

Rodeo®/R-11®

17.89

31.53

****

****

a when residues are the result of drift to water

b Monsanto 1983a and 1983b

c when residues are the result of direct application to water

Toxicity Tests with Undiluted Site Water

In addition to determining the 96-h LC50 values for Rodeo® and Rodeo®/R-11®, water samples collected from waterways directly adjacent to the herbicide/surfactant applications were tested, without dilution, for toxicity to larval Rana. The samples were collected one hour after the herbicide/surfactant applications. No significant mortality (p<0.05) was observed in these tests.

Discussion

The information produced from this study indicates that Rodeo® with R-11® applied aerially to control giant cane poses no significant acute toxicity hazard to nontarget fish and frog species. Herbicide and surfactant residues were 100 to 10,000 times less than would be necessary to produce acute mortality.

Literature Cited

Bidwell, J.R. and J.R. Gorrie. 1995. Acute toxicity of a herbicide to selected frog species. Final report prepared for the Western Australian Department of Environmental Protection. 9 pp.

California Department of Fish and Game (CDFG). 1994. Amphibian and reptile species of special concern in California. Final report submitted to the California Department of Fish and Game, Inland Fisheries Division, Sacramento, CA. 1994.

CDFG. 1998. Quality Assurance Project Plan. Control of giant cane (Arundo donax) in riparian and wetland areas of northern and central California. California Department of Fish and Game, Pesticide Investigations Unit. September 1998.

Monsanto 1983a. Unpublished data. Acute toxicity of R-11 (AB-83-063) to rainbow trout (Salmo gairdneri). Produced by Analytical Bio-Chemistry Laboratories Inc., Columbia, Missouri for Monsanto. April 1983.

Monsanto 1983b. Unpublished data. Acute toxicity of R-11 (AB-83-063) to bluegill sunfish (Lepomis macrochirus). Produced by Analytical Bio-Chemistry Laboratories Inc., Columbia, Missouri for Monsanto. May 1983.

Task 3: Public Education

This task involved the production and distribution of materials that will be used to educate the public about the ecological threat posed by giant cane and to enlist the support of private and public organizations in local giant cane control projects. This task was conducted under contract with California State University at Sacramento. The tri-fold brochure, Arundo Streamside Invader, includes full-color photos and introductory information on giant cane. 8,000 copies of the brochure were produced. A professional quality video, Controlling Arundo in Your Watershed, was also produced. Copies of the video will be made available to watershed groups and other environmental organizations.

This task also produced two guidebooks. Controlling Arundo in Your Watershed: a Guide For Organizations was developed to assist public and private organizations in recruiting landowners in giant cane removal projects. It includes information on organizing projects, public agency permits and working with volunteers. Arundo: A Landowner Handbook presents basic information on giant cane identification, biology and the ecological damage it causes. It also discusses the primary methods used for giant cane control including physical removal and herbicide use.

Distribution of the educational materials will be conducted by Team Arundo del Norte (TAdN), a multi-stakeholder partnership dedicated to giant cane control in northern and central California. TAdN participants include representatives from public agenicies such as the United States Environmental Protection Agency, the California Department of Water Resources and the California Department of Fish and Game, academia including the University of California - Berkeley and private organizations such as the Sonoma Ecology Center and the Cache Creek Conservancy.