Controlling Japanese barberry (Berberis thunbergii DC) in southern New England, USA

Dense Japanese barberry (Berberis thunbergii) stands have spread beyond manicured landscapes and are associated with a paucity of both tree regeneration and herbaceous plants in some forest stands. Studies over 2 years evaluated the effectiveness of various treatment alternatives to control barberry. A total of 375 barberry clumps at three study areas were selected for the first study in 2006. Treatments included directed flame using a 100,000 BTU propane torch on the following schedule: (1) pre-leafout and no follow-up treatment in July, (2) pre-leafout with directed flame in July, (3) post-leafout and no follow-up treatment, (4) post-leafout with follow-up treatment, and (5) untreated controls. Clumps treated once had higher mortality (45%) than untreated clumps (3%), but timing of initial treatment did not affect clump mortality. Clumps treated twice had the highest mortality of all (74%). All propane torch treatments reduced clump size, on average, by nearly 75%. Size of untreated clumps increased by 13%. In 2007, a two-step process to control barberry was examined for 1100 clumps at six study areas. Initial treatments (prescribed burning, mechanical mowing with a drum chopper or with a brush saw) were applied to reduce the size of established barberry clumps. The second, follow-up treatments in mid-summer that treated new sprouts included foliar application of triclopyr or glyphosate, directed flame, and untreated controls. All initial treatments were equally effective in reducing clump size. Mortality differed among follow-up treatments: untreated controls (14%), directed flame (40%), and herbicide (93%). Surviving clumps having no follow-up treatment recovered to half of their original size by the end of the growing season. Size of surviving clumps did not differ among the other follow-up treatments and averaged 20% of the original size. Excellent control of Japanese barberry can be achieved using either propane torches or herbicides. Propane torches provide a non-chemical alternative where in parks, nature preserves, or forests where herbicide use is restricted and where barberry infestations are still light. (C) 2008 Elsevier B.V. All rights reserved.