Invasive Plant Control at Glacial Heritage Preserve

Transcription

1 Invasive Plant Control at Glacial Heritage Preserve The Black River-Mima Prairie-Glacial Heritage Preserve is located in southern Thurston County, southwest of the town of Littlerock. It contains four main habitat types, Oregon white oak woodland, prairie grassland, riparian woodlands, and coniferous forest. Each of these habitats contributes to the overall biodiversity of the preserve and creates an important mosaic of habitats crucial for the survival of a wide range of plants and animals. Glacial Heritage is a key component in the network of nature preserves helping to conserve one of the rarest ecosystems in Washington. The control of biological threats continues to be a high priority at Glacial Heritage Preserve. The major biological threats present on the site are Scotch broom, invasive grasses, and invasive conifers. Addressing these biological threats is critical in keeping with each of the strategic goals for the preserve. For example, reducing the density of infestation of Scotch broom across the preserve and expanding the areas free from Scotch broom enables Glacial Heritage to act as a core holding for conservation in the South Puget Sound region. The integrated techniques that are used to control biological threats, such as Scotch broom, also allow the preserve to serve as a demonstration site for restoration strategies and techniques. Impacts Eurasian grasses introduced as forage for livestock or as lawn grasses are a problem because they do not provide the vegetation structure or species composition required for many native animals. Tall oat grass is an especially damaging invasive grass, as it alters the structure of the prairie drastically. Several of the species of conservation concern including the mardon skipper are dependent on the native bunchgrass community, which is choked out by high densities of invasive grasses; native forbs that serve as host plants for butterflies are also lost. Tall oat grass in particular has expanded voraciously across the preserve in the last eight years, from virtually non-extant to pervasive across all areas surveyed. Control options: Cultural Techniques Non-native grasses are present in nearly all native grasslands, due to their heavy use for pastures, hay and lawns. Isolation from seed sources: Glacial Heritage is isolated from further invasion by tall oat grass through its position between a wide riparian corridor and a series of farms that

2 rigorously control their weeds. The only likely continuing infestation is from adjoining county lands, and those lands are heavily infested with Scotch broom, which may minimize movement of seed. The adjoining county lands also lie upwind of the preserve. Restoration: The rapid infestation of non-native grasses is believed to be a result of open ground exposed by the removal of Scotch broom from the preserve in the last eight years. Since bunchgrasses and native forbs develop more slowly than non-native grasses, exposed areas can be overwhelmed before the native community can naturally regenerate. In order to address this problem, exposed ground created by the removal of tall oat grass will be replanted with natives to prevent the re-invasion of tall oat grass or an increase in other exotic weeds. Manual Techniques Hand pulling: Hand pulling tall oat grass is ineffective for both biological and scale reasons. Biologically, tall oat grass has bulblets on its root crown, which can reproduce asexually, and pulling may encourage it to spread by creating new plants. With regards to scale, we have six hundred acres of prairie at Glacial Heritage, most of which is more or less infested with tall oat grass. Hand pulling to control the problem would be an exercise in futility. Mowing: Mowing has slight efficacy against tall oat grass, control will take five years or longer. Furthermore, mowing takes place when our ground nesting birds are raising their young and our prairie butterflies are active. Mowing therefore presents an unacceptable level of risk/mortality to our target conservation species. Fire: Fire has not been shown to be effective at reducing tall oat grass populations. Chemical Techniques Glyphosate (Roundup): Glyphosate is a non-selective herbicide that is permitted for use on county lands. We were able to use this herbicide to treat Scotch broom due to its timing and height differences from native plants. Tall oat grass, however, is susceptible to herbicide in the spring when it is the same height as the native plants, which makes a wiping technique inapplicable. Except where tall oat grass stands are extremely dense, the tall oat grass infestation is heavily mixed with slow-growing natives, and use of a non-selective herbicide will cause unacceptable levels of mortality to the native prairie plants, leaving more space open for further weed invasions. Sethoxydim (Poast): The herbicide sethoxydim is effective at controlling non-native grasses without damage to the native narrow-leaf bunchgrass that is the foundation of our prairie structure and a host plant for native butterflies, and is also safe to apply over forbs. Sethoxydim failed the county review due to possible chronic reproductive toxicity to birds when applied at the label rate over the entire area in which a bird feeds. The brand Poast had a second failure due to the carrier used in the brand mix, 74% naptha, which is an EPA List 2 inert ingredient. Poast also contains up to 7% naphthalene which is classified as a Group 2B chemical (possibly carcinogenic to humans) by the International Agency for Research on Cancer. While Poast was the preferred grass specific herbicide in previous years, regional land managers have switched to Fusilade DX (fluazifop-pbutyl) based on experimentation that has shown Fusilade to be more effective. Fluaziflop-p-butyl (Fusilade DX): Fluazifop-p-butyl has become the preferred grass specific herbicide of choice for regional natural areas managers. An increased focus on tall oatgrass control generated interest in herbicides other than Poast and experimental trials were initiated in 2007 by The Nature Conservancy on Fort Lewis. The results clearly showed that Fusilade offered better control of tall oatgrass when compared with Poast; see graph and analysis below. Vegetation managers at Scatter Creek NAP also

3 performed similar herbicide comparisons and drew the same conclusions. Fluazifop herbicides also failed the county review because they contain ~4% naphthalene and pose some risk to human applicators and people who might make contact with recently treated vegetation. These risks will be mitigated by handling and spraying techniques that minimize exposure to staff. Full personal protective equipment will be used by applicators, including long sleeved shirts, long pants, socks, boots, eye protection and chemically resistant gloves; when mixing and loading a chemically resistant apron will be utilized. The treated areas will be clearly demarcated and entry will be restricted for 24 hours after application. Figure 1 Comparing Fusilade and Poast control using avergage percent cover of tall oatgrass Table 1: Between subject effects Pre-trt vs. 1yr Post Pre-trt vs. 2yrs Post 1yr Post-trt vs. 2yrs Post-trt Fusilade F=128.08; p< F=34.31; p= F=1.00; p= Poast F=12.74; p= F=11.86; p= F=5.97; p= Table 2: Within subject effects Pre-trt 1yr Post-trt 2yrs Post-trt Fusilade vs. Poast F=1.46; p= F=19.13; p= F=3.46; p= Spray Procedure Areas to be sprayed will be posted before application begins, and will remain posted with no entry signs for at least 24 hours after application. Volunteers and staff visitors will be instructed to stay out of posted spray areas. Areas to be sprayed will be checked for ground-nesting bird nests, and a 50 no-spray radius will be observed around any nests found.

4 Control typically begins in early spring, with the maximum allowed rate of 24 ounces/acre or pounds of active ingredient/acre (0.75% by volume for back pack/spot treating) of Fusilade DX plus a non-ionic surfactant. Application should be made in the spring and/or fall when plants are about 12 inches tall. Height is important, as it represents the growth stage and herbicide susceptibility of the plant. The label prohibits spraying over water or intertidal areas: this prescription further requires that spraying not occur within 100 of open water or standing water. Fusilade DX will be applied in a given area over two years, using the same rates of concentration. Once the tall oat grass cover has dropped to <10% cover, replanting of natives will help reduce the influx of new weed germination. Timing The time that tall oat grass is vulnerable to systemic herbicides is in April and early May, when the majority of our native prairie forbs are leafed out and many are in full bloom, and in the fall when the plant is transporting nutrients to the roots for the winter. This timing issue precludes the use of a non-selective herbicide such as glyphosate. Map Treatment will be based on prairie quality, wildlife use and tall oat grass density. For example, the large pastures at the western edge of the preserve will be sprayed using a tractor, as the native grasses density is low and the tall oat grass density very high, with a population of long-lived perennial forbs that are the sole host plant for one of our rare butterflies intermixed with the tall oat grass. In the central portion of the prairie, spot spraying will be used to target small and medium patches, with a tractor used where spot spraying is impractical.

5 Concerns The Nature Conservancy practices adaptive management, and constantly searches for the lowestimpact, most effective treatments for management techniques. As we move forward on an everevolving cycle of restoration actions to benefit the prairies of Glacial Heritage, we continue to learn which tools are most effective. It has been consistently demonstrated, for example, that

6 Fusilade DX is a more effective control for tall oatgrass when compare to Poast. Fusilade DX may require less frequent herbicide application and/or less applications to achieve control than Poast. While we acknowledge the risks of using Fusilade DX, if no action is taken, the native grassland plants and animals will lose their habitat to invasive this weed. By approving the use of Fusilade DX, Thurston County and The Nature Conservancy will work together towards restoring the natural balance of this globally rare ecological community. Other Herbicide Applications This section is a review of other herbicide applications that take place at Glacial Heritage. Glyphosate (Roundup): Glyphosate is often used within two weeks of a prescribed fire to control invasive forbes and grasses that emerge before native vegetation. Aminopyralid (Milestone VM): Aminopyralid is used to a limited extent to treat invasive forbes from the aster family such as Hypochaeris radicata (hairy cat s ear) and Leucanthemum vulgare (ox-eye daisy). Aminopyralid is recommended by Thurston County as a chemical treatment for other asters such as hawkweeds, knapweeds and thistles. Currently, no invasive hawkweed or knapweed species occur at Glacial Heritage, but aminopyralid would be used if they were found. Triclopyr ester (Garlon 4): Triclopyr ester is part of an integrated control strategy for Scotch broom. Hand pulling, mowing and prescribed fires are the preferred control methods for Scotch broom. Triclopyr is used in areas where other forms of control are not practical. Thurston County recommends using glyphosate (Roundup) for chemical control of Scotch broom; however, since glyphosate is non-selective it will also harm native plants and therefore is not a sensible option. Triclopyr is a broadleaf specific herbicide, so it does not affect grass species; it is applied in the late summer (September) when the majority of native plants have senesced. Clethodim (Envoy): Clethodim is a grass specific herbicide similar to sethoxydim and fluazifop. Clethodim passed review by Thurston County and its potential hazard to humans is low, as compared to the potential high hazard from sethoxydim and fluazifop. Trials are expected to be initiated in 2011 to determine effectiveness on target plants and to ensure that it, like sethoxydim and fluazifop, it does not harm native fescue and carex species. If the trials are successful, then a transition to this more environmentally friendly herbicide will likely take place in the future. Updated by: Casey Dennehy; The Nature Conservancy; 120 Union Ave SE #215, Olympia, WA 98501; cdennehy@tnc.org; (360)