I recently heard Dr. Mark Brand from the University of Connecticut speak about his work evaluating cultivars of Japanese barberry (Berberis thunbergii), an invasive plant species. For over a decade, Dr. Brand has been studying and assessing the invasive potential of different cultivars to determine whether or not the entire species should be banned here in Connecticut, or if some of the cultivars are, essentially, seedless and therefore will not become invasive. Brand has also used the knowledge gained from his work to breed several new compact sterile cultivars of Japanese barberry.
I can hear some of you saying…hold on…who cares if the entire species if banned? And why on earth would we want to promote the landscape use of any cultivars of a plant like Japanese barberry? How do we know that these cultivars aren’t cross-breeding with the species? Have we learned nothing from past experience?
A Different Path
Unlike many states, Connecticut decided against an outright ban of Japanese barberry and instead growers agreed to voluntarily ban 25 Japanese barberry cultivars, based in large part on Dr. Brand’s initial research findings. Admittedly, this voluntary ban is somewhat self-serving for growers. According to the Connecticut Nursery and Landscape Association, the revenue from the 25 banned cultivars in Connecticut alone is over $5,000,000 annually. I couldn’t find figures on the revenues from Japanese barberry cultivars still on the market, but I imagine the number is also quite high.
It’s All in The Genes
I’m not a scientist, nor do I play one on this blog. While I understand the basic science behind Dr. Brand’s work, I am in no position to defend it. Having said that, I can tell you that Brand and his colleagues used AFLP marker technology to look at genetic markers in stands of invasive Japanese barberry at different sites near UCONN to determine its origin and to see if wild populations could be linked genetically to cultivars. In essence, are cultivars planted in our home landscapes ‘escaping’ into nearby wild areas.
Brand’s team found seed production in cultivars of Japanese barberry varies radically. For instance, Golden Devine (Berberis thunbergii ’Golden Devine’) has no seeds while one Emerald Carousel (Berberis thunbergii ‘Tara’) shrub had almost 10,000! In general, Brand found that tall green-leaved cultivars tend to produce copious amounts of seed while compact yellow or purple-leafed cultivars tend to produce the lowest amount of seeds.
Based in part on germination rates (15 – 30%) and seedling survival rates (10 – 20%), Brand determined Japanese barberry cultivars with 50 or fewer seeds per plant can be considered non-invasive. He also found plants really need to be evaluated for a much longer time frame than is typically done by growers to accurately determine seed production. Evaluating cultivars for seed production, or sterility, after only a year or two can be misleading. Brand’s team tested cultivars in landscape situations for almost a decade and found seed production often increased, sometimes dramatically, as plants matured.
The Wave of the Future
Whether you agree with Connecticut’s approach to dealing with Japanese barberry (Berberis thunbergii) or not, this science-based approach to evaluating cultivars of invasive species, rather than painting them all with the same broad brush, may be the future of dealing with invasive plants.
Some states are already beginning to follow Connecticut’s research driven approach to regulating invasive plants. Recommendations from Minnesota’s Noxious Weed Advisory Board specifically reference Connecticut’s methods. In Oregon, a state known for its strict invasive plant policies, several new ‘sterile’ cultivars of butterfly bush are being sold after years of an outright ban on the species. Is this progress or a step in the wrong direction?
Through his research, Brand found that when breeding new cultivars of Japanese barberry, mixing together three different species virtually eliminates seeds in cultivars. UCONN hopes to introduce six sterile cultivars of Japanese barberry in the near future. Breeding is also being done by Dr.Thomas Ranney at NC State University. So whether you’re on board or not, it’s time to get ready for the arrival of sterile cultivars of Japanese barberry in your local nursery.
Frankly, I’m not entirely sure how I feel about these potential seedless Japanese barberry cultivars. In an ideal world, I’d like to see an outright ban of Japanese barberry here in Connecticut. But regulation based on empirical data appeals to the pragmatist in me. Still, I’m worried about the coulds and what ifs. Research has also shown that some exotics lay low in the landscape for years before becoming invasive. On the other hand, one of the realities of today’s economy is that funding for some state invasive plant programs is disappearing. Will these sterile interspecific hybrids mean that once condemned invasive plants find new homes in our landscapes?
Education is an important component to the problem of invasive plants and helping gardeners find native plant alternatives to invasive plants is a key to dealing with the problem, even as sterile hybrids begin to find a place in local nurseries.
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