Summary of Arundo Control Methods

CHEMICAL APPLICATION

FOLIAR HERBICIDE APPLICATION

This method involves spraying herbicide on the stems and leaves of Arundo without any cutting. The herbicide that has been found to be most effective is a glyphosate. If treatment is in or adjacent to water then Rodeo^® must be used because it is approved by the EPA for use in wetlands. Monsanto label recommendations for Rodeo^® use on Arundo are to use 2% solution. However, field tests have indicated that a low rate of kill is achieved with 2% foliar application. A much higher kill rate (up to 95% with one treatment) has been achieved when using a higher percentage (5% to 6%) - see photos below. The leaves and stems need to be thoroughly sprayed - in some cases this is difficult due to the height of the vegetation and the presence of non-target vegetation nearby. Pressurized sprayers (mounted on an ATV) and the use of ladders are helpful where the Arundo is tall. In some cases non-target plants can be trimmed if there is concern of overspray. Most native woody riparian species (e.g. willows) resprout vigorously after being cut back. However, please make sure there are no restrictions on trimming native vegetation first. The Arundo can be 'prepped' prior to spraying by pulling the stem away from non-target vegetation and pushing it down to the ground. Because the Arundo rhizome mass remains in the ground, if a sub-lethal dose of herbicide is applied, then resprouting will occur. Therefore, this method REQUIRES follow-up for at least three years and preferably five. Resprouting of a foliar sprayed Arundo plant has occurred after several years of showing no growth and looking 'dead.'  While some resprouting usually does occur, it is generally composed of very scattered, small Arundo sprouts.

If the dead Arundo biomass is not a concern then it can be left on site to decompose naturally (see photos below). However, if the presence of dead Arundo stems is a concern (flood hazard, fire hazard, aesthetics, in the way of replanting, etc.) then the stems can be removed. The main point here is that the stems should not be cut too soon after the herbicide application otherwise the herbicide does not fully kill the plant and resprouting occurs. It is not certain yet what the 'ideal' amount of time is between foliar spraying and stem cutting, but this is currently being investigated. From our experience it seems as though ideally the Arundo plants should be left standing for at least a year after the foliar herbicide application. However, recent control projects around the town of Fallbrook indicate that there is good kill even when the stems are cut only 4-6 months after foliar herbicide application. However, this is only the first year of this project, so how much repsrouting may occur in future years is uncertain. For a summary of options for dealing with Arundo biomass see: What to do with Arundo biomass  

PROS:

• Can be a very successful treatment with only one main herbicide application, and follow-up treatments that require much less herbicide and effort.
• No mechanical disturbance to the soil or vegetation. This may be an important consideration where endangered species such as the arroyo southwestern toad may be impacted, or if there is concern about non-native herbaceous plant colonization post-treatment.

CONS:

• This method requires herbicide use which may be a problem in some areas.
• Herbicide overspray onto non-target plants may be a concern. Overspray can be reduced, as described above. Sprayed plants must be monitored to check for resprouting, and resprayed as necessary. Ideally we think monitoring should be carried out for 5 years.
• Above and below ground Arundo biomass is left on site - this may be a concern in situations where the aboveground biomass may be a fire or flood hazard. The aboveground biomass may be removed, however, the stems should not be cut too soon after herbicide application. If enough time has not passed between spraying and cutting, the herbicide does not fully kill the plant and resprouting occurs. See discussion above for more details on dealing with the biomass.

IMAGES OF:

Foliar spraying Arundo: large and small

Stand of foliar sprayed Arundo: before and after