Connecticut’s woodland undergrowth is beginning to green. Unfortunately, much of this color is due to invasive Japanese barberry (Berberis thunbergii de Candolle). This thorny shrub dominates unmanaged wooded areas. Deer don’t eat it and birds spread it by eating and dispersing the prolific red berries it produces each autumn. Japanese barberry quickly grows into large thickets that provide cover for mice and an ideal environment for immature blacklegged ticks – the very ticks that carry Lyme disease. In their early life, ticks are susceptible to desiccation – they need high-humidity at the ground level to thrive. Japanese barberry accommodate the high-humidity needs of young ticks by leafing out earlier than most native shrubbery, thus maintaining ground-level moisture by blocking drying sunshine.
Mice also like the protection a large stand of Japanese barberry affords them from predators. With mice and ticks enjoying the same habitat there’s bound to be an increase in tick-borne disease.
Researchers Scott C. Williams and Jeffrey S. Ward, at the Connecticut Agricultural Experiment Station in New Haven, have been monitoring the number of mice, the number of ticks and Lyme-infected ticks, and ground-level humidity in three geographic areas of Connecticut. In each area they have test plots of uncontrolled, controlled, and no Japanese barberry. They control Japanese barberry in their test plots using one of three methods. One method is torching the base of each shrub until the main stems carbonized and glowed – in effect girdling main stems to stop nutrient transfer. I would not advise trying this method without undergoing a certain level of training, particularly during this dry, high fire risk spring of 2012.
The other two forms of control involved mechanically cutting the shrubs – usually by brush hog – and leaving cut plant material in place. They controlled regrowth with herbicides or flame from a propane torch applied directly to new sprouts. Note: Torching is acceptable control method for organic land care. It involves heating new sprouts by sweeping the flame back and forth over leaves until their cells burst. Torching does not involve turning a large patch of land into a flaming inferno. However, in this dry and high fire risk year, I strongly suggest this type of control only be used by highly trained individuals.
With a total of three years of data now collected, Williams and Ward report plots without barberry have about 30 Lyme-infected ticks per hectare (the equivalent of 2.471 acres). In these controlled plots, the researchers found decreased humidity and ‘a near 60% reduction in the number of B. burgdorferi-infected adult blacklegged ticks.’
Plots of uncontrolled Japanese barberry had about 280 Lyme-infected ticks per hectare.
These findings suggest that continued barberry control will result in continued decline in tick populations. Mechanical control takes vigilance and follow-up, as Scott Williams explained for my report on his and Ward’s previous Japanese barberry-tick study. Effective eradication requires proper identification of the Japanese barberry shrubs, mechanical removal of all above-ground portions in late-spring or early summer so the shrubs use starchy root reserves to force out new growth, then killing new growth in later summer.
It is extremely important to know that Japanese barberry shrubs will not die with one cut. Williams cautions that cut shrubs send up new growth with a vengeance. If pulled, it will resprout from the tiniest rootlets left in the ground. Re-checking areas where Japanese barberry has been cut or pulled is an extremely important management practice. Eradication requires vigilance.
I live in an area heavily infested with Japanese barberry yet my property is clear of this invader because I wander my property this time of year to attack any Japanese barberry shrub or sprout. I repeat my wanderings during autumn months to be sure the invaders remain under control. If wooded areas adjacent to your home are so overgrown with this invasive shrub that control there seems impossible, then take the time to establish a line in which you will not let Japanese barberry cross. Keep it from establishing in the areas your family and pets frequent.
With little practice, spotting and removing Japanese barberry will become part of your regular gardening routine.
Note: this is a rewrite of a previous post, Lyme-ticks thrive in Japanese barberry thickets.