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Japanese barberry infestations and their impact on human health

Kathy Zuzek, UMN Extension Educator

Japanese barberry.  Photo: K. Zuzek
Japanese barberry is a popular landscape shrub known for its bright foliage color, attractive flowers and fruit, a wide variety of plant habit, and its deer resistance. More than 80 cultivars have been developed since it was first planted in the U.S. in the late 1870s. But Japanese barberry is also an invasive plant that has naturalized in more than 30 states across the U.S. 

In January of 2015, Japanese barberry was listed as a noxious weed in Minnesota. There is a wide variety of seed production among barberries and the 26 seediest cultivars, identified by research at the University of Connecticut, are being phased out of nursery production over a three-year period. On January 1, 2018, these cultivars will become restricted noxious weeds in Minnesota and their propagation and sale will be illegal. 

Minnesota noxious weeds are plants designated by the Commissioner of Agriculture to be injurious to public health, the environment, public roads, crops, livestock, or other property. Japanese barberry does harm Minnesota’s environment. The fruit are an attractive food to birds who disperse seed into native areas and allow barberry to escape from landscape plantings. Barberries establish in the undergrowth of forested areas where they alter soil characteristics and often form thickets that outcompete and displace native plants. 84 incidences of barberries in native ecosystems have been reported in Minnesota.

Blacklegged tick.
Photo:  S. Bauer,
Research studies in Maine and Connecticut have shown that Japanese barberry also has an indirect negative impact on human health. Thickets of invasive barberry harbor provide microclimates without large swings in temperature and relative humidity. As it turns out, that microclimate is a very desirable habitat for blacklegged ticks infected with Borrelia burgdorferi, the causal agent of Lyme Disease. Research at the University of Connecticut found 30 B. burgdorferi-infected adult blacklegged ticks/hectare in areas without barberry infestations, 280 in full barberry infestations, and 121 in areas where barberry infestations had been controlled.

Tick drag.  Photo:  F. Dorr,
 MN Dept. of Health
A pilot study undertaken by the Minnesota Department of Health is underway to verify whether the same trend of increased B. burgdorferi-infected tick levels in barberry-infested sites is occurring in Minnesota. During an initial survey last fall, a barberry stand was sampled using a tick drag (a weighted 1x1 meter canvas cloth that is dragged through vegetation). Ticks were collected from the drag, counted, and their species, sex, and condition were recorded. Both wood ticks and blacklegged ticks were found.

During 2016, the Minnesota Department of Health is partnering with the University of St Mary’s in Winona, MN to survey two barberry infestation sites located in Wabasha and Houston Counties. Two additional sites without barberry infestations will also be surveyed. Sampling in spring and fall will harvest adult ticks and June sampling will collect ticks in the small nymph stage. On each sampling date, a 100-meter transect will be dragged along a trail’s edge bordering either barberry or native vegetation. Ticks will be harvested and counted so that comparisons can be made between barberry-infested sites and non-infested sites.  Species and sex of collected ticks will also be noted. Ticks can be preserved and sampled later for the presence of three common tick-vectored diseases: Lyme Disease, granulocytic anaplasmosis, and babesiosis.                     


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