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Funded Project |
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Funding Program:
IPM Partnership Grants |
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Project Title:
Barberry removal to decrease Lyme disease risk: a demonstration project
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Project Directors (PDs):
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Lead State: ME Lead Organization: Maine Medical Center |
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Cooperating State(s):
Maine |
| Undesignated Funding: $37,991 |
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Start Date: Apr-01-2013 End Date: Feb-28-2014 |
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No-Cost Extension Date: Aug-31-2015 |
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Pests Involved: Ixodes scapularis |
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Site/Commodity: Southern Maine |
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Area of Emphasis: organic/invasive species/human health |
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Summary:
This proposal addresses two burgeoning, inter-related problems in northern New England, tick-borne diseases and the invasion of northeastern forests by Japanese barberry. Three previous studies report higher abundance of Ixodes scapularis, the deer tick vector of Lyme disease, in barberry habitat, and up to 60% reduction following barberry removal. The plants impenetrable structure and aggressive dominance not only prevent establishment of native growth but also provide sanctuary for tick hosts. The goal of this project is to expand on previous findings to increase the publics awareness of the benefits and importance of removing barberry. We will achieve this by measuring the effect of barberry removal on questing deer tick abundance and infection prevalence using multiple sections of recreational trails in southern Maine. From this we will prepare materials for presentation to stakeholders and the public via the internet, print and electronic media, and presentations to target audiences, with the goal of increasing barberry removal for the benefit of both the environment and public health.
Objectives: 1. To measure the impact of barberry removal on the abundance of the deer tick, Ixodes scapularis, vector of Lyme and other tick-borne diseases to humans. 2. To use these data to encourage barberry removal through the networks of stakeholder organizations related to property management, outdoor recreation/occupation, conservation, silviculture, & public health. |
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Interim Report: Sep-16-2014 |
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Impacts Impacts Safeguarding human health and the environment: Removing tick habitat is a major component of tick IPM in both private and public properties and the value of its application needs to be realized, particularly in areas of high infestation. Tick abundance is rising in northern New England, where per capita Lyme disease cases are highest in the country and at least three other diseases are being transmitted by deer ticks. The failure of our project to date to provide supporting evidence was caused by inadequate treatments, an issue not to be encountered by the total removal of tick habitat on 3-4 infested acres. Economic benefits: Removing exotic invasive species is a labor intensive effort that most landowners will be glad to have professional help to accomplish. On the other hand, this cost should be considered in light of the economic impact of the medical treatment of tick-borne diseases, not to mention the suffering. Implementation of IPM: Not yet applicable |
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Outcomes Outcomes In year one, 2013, after the treatment, fall-flagged adult ticks on control and treated plots did not differ. This is not surprising, since this adult cohort would be the fed and molted nymphs from the nymphal cohort of the summer, which occupied treated plots before the barberry was cut. However we are concerned that 1) ticks can be more efficiently flagged on the cut plots, and/or that 2) adult ticks could have quested out from the edges of the uncut barberry. Since the plots were cut to a 1m width rather than a 4m width, this is a potential problem. The team decided to widen the 1m wide plots to 2m (the maximum allowed at the Wells site) in 2014, even though this necessitates a one-year non-cost extension of the project. Infection of fall-flagged adult ticks by B. burgdorferi was ~60%, typical for the towns sampled. The entomological risk index (infected ticks encounter rate) was a little over 50 per hour, or nearly one per minute. Unexpected Events and Challenges: Cape Elizabeth: " Treatment plots cut only 1m deep due to miscommunication " Extreme fern growth hindered flagging on some transects, especially during nymphal season " Bittersweet and Japanese honeysuckle took over plots where only barberry was cut " Thus no flagging in 2014 Wells: " 2013 treatment plots cut only 1m deep due to miscommunication " 2014 Reserve allowed re-cut to 2m width (but not 4m width as planned) " Wells Reserve cut some control plots, effectively creating control plots, but uneven sample number of plots per treatment will not affect statistical analysis Lane Island " Island used by recreational boaters who land and walk (day visitors and overnight campers) " Acquired by Maine Coast Land Trust in 2014, native oak-pine forest becoming overrun with Japanese barberry, Eurasian honeysuckle (Lonicera spp.), bittersweet (Celastrus orbiculatus), and common buckthorn (Rhamnus spp.); MCHT asked MMCRI VBDL if would partner to study effects of treatment with a fall 2014 cut-stump treatment of Roundup followed by a foliar spray " Transects established through planned control and treatment areas and ticks sampled in July 2014 " Treatment area is one 3-4 acre plot; week of September 22nd will be treated with a cut-stump treatment of Roundup followed by a foliar spray in spring of 2015 at leaf-out |
Report Appendices
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Final Report: |
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Impacts To determine treatment effects while accounting for time, we used generalized linear mixed models, one each for adults and nymphs (proc glimmix, SAS Institute 2008) of the form y = C² + Zm + e. We used a negative binomial response for the count data. The linear part of the model, C², was tick count = ²0 + ²1treatment + ²2before/after + ²3treatment × before/after, while allowing for random effects (Zm, spatial and temporal correlations among plots within transects). A significant interaction between treatment and time (P £ 0.05) would indicate that tick abundance on treated plots changed after treatment, relative to reference plots. We assessed model fit using the Pearson c2/DF statistic which should be close to 1.0 (McCullagh and Nelder 1989). We plotted Pearson residuals and against the linear predictor, with residuals approximately c2 distributed with 3.8 as the approximation to the 95th percentile and a suitable fit concluded if 95% of the outliers in the plots fell below 3.8 (Hosmer and Lemeshow 2000). There were no significant random effects and so the adult and nymphal models reduced to generalized linear models. Model fit was suitable for the nymphal and adult models, Pearson c2/DF=0.93-1.02, residuals approximately c2 distributed and 95% <3.8. We also used a generalized linear model to test for differences in number of barberry clumps per size class. The model was clump count = ²0 + ²1treatment and there were no significant random effects. |
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Outcomes The barberry treatment as prescribed did not reduce adult and nymphal ticks in any season. (time x treatment interaction insignificant (P=0.08 nymphs, P=0.66 adults, Table 1, Table 2, Fig. 1). Furthermore, regeneration of barberry clumps was robust (Table 3). Although there were significantly fewer clumps in treated plots than in reference plots in the small and medium size classes, it was observed that medium-sized clumps thought dead were still alive and appeared healthy in the growing seasons following the August 2013 and 2014 treatments. Vigorous sprouting at the ground level in the small size class was also evident. Two explanations for lack of tick control through the selected treatment include: 1. Ticks could have quested out from the edges of the uncut barberry, since the plots were cut to only a maximum of 2m width, and 2. Residual stems of shrub vegetation, and rapidly regenerating barberry sprouts, provided adequate perches for questing ticks Complete lack of tick control was an unexpected outcome, given that in Connecticut, barberry removal resulted in a 60% reduction in tick abundance (Williams et al. 2010). However, in that study, large grids were treated (30 x 30m and 50 x 50m), and tick-sampling was done along transects within the grids. Our transects ran parallel to uncut habitat. Our conclusion is that the narrow transects (2m wide) were infested with ticks because they were adjacent to tick-infested habitat, and both adult and nymphal ticks quested out into the cut plots, where regenerating barberry provided questing substrate. |
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