January Weed Of The Month: Japanese Barberry And Ticks

 

In last month’s Weed of the Month article, we introduced the invasive shrub Japanese barberry (Berberis thunbergii). This shrub has escaped landscape cultivation in Minnesota, naturalized in our woods, and is threatening our native habitats. This month, we will explore the interesting connection between Japanese barberry, ticks, and Lyme disease.

 

Researchers in Connecticut found that there is a higher density of blacklegged (deer) ticks carrying Lyme disease in barberry infestations than in other habitats. Japanese barberry infestations create an ideal, humid environment for ticks. As a result, blacklegged ticks can reach higher densities in these areas.

 

In Minnesota, we commonly think of deer as being the main food source for ticks. In fact, they are but one vector for ticks, and by extension, Lyme disease. White-footed mice and other rodents are important vectors for immature ticks, and are the primary sources for a tick larva’s first blood meal. Mice thrive in stands of Japanese barberry; the dense, impenetrable stands protect them from predators and provide optimal nesting sites.

 

The high populations of ticks, combined with the high populations of rodent vectors result in higher levels of Lyme disease in Japanese barberry infestations. This is especially concerning for humans, as the majority of Lyme cases occur as a result of nymphal tick bites.