Nebraskaland

44 Nebraskaland • May 2020 avoids the use of harmful chemicals on the ecosystem. NPLT biologist Chris Wood, who helps manage the infestation in northeastern Nebraska, said that a follow-up prescribed burn is imperative to controlling garlic mustard. "Something I've noticed is that if you conduct a woodland burn in the fall and don't follow up with a burn the following year, it seems to help garlic mustard spread even faster," Wood said. "Basically, a fall burn will clean up the debris, release nutrients and create a perfect space for garlic mustard to grow. Burning two years in a row will help knock back some second-year growth by potentially killing plants and reducing seed production, in addition to killing seedlings, which will reduce an infestation over time." The best plans incorporate all three methods. What Landowners Should Do Once established, management of garlic mustard will be time consuming and ongoing. Early detection is key. "It's the 'ounce-of-prevention-is-worth-a-pound-of-cure' concept," said Cassidy Wessel, a Game and Parks Commission biologist in Norfolk. "As some invasive species become established, they create a positive feedback loop, altering soil chemical properties through allelopathic traits, building up a seed bank and so on. The longer you wait, the tougher it gets to control it." Allelopathy is when an organism produces one or more biochemicals that are released through its roots into the soil, making growing conditions less tolerable for other species. It's a strategy some plants use to outcompete others, and in the case of garlic mustard, that is the chemical sinigrin mentioned previously. If a landowner detects garlic mustard on his or her property, Brueggemann recommends taking the following steps. Step 1: Determine the area of the infestation. "Usually by the time a landowner notices an infestation of invasive plants, the population size is often larger than one thinks," he said. Step 2: Begin control on the smaller, outlying populations of the infestation and then work inward toward the areas of higher densities. Step 3: Revisit the area annually and continue controlling the plants. "Similar to other invasive or exotic species, once garlic mustard is well established it will be hard to eradicate," Wood said. "However, through the various control methods mentioned, it could be managed to the point where it's not damaging woodland ecosystems." Studies Debate exists among experts on the necessity of controlling garlic mustard. Lang referenced a handful of land managers who have stopped actively controlling garlic mustard by pulling and spraying, and are only employing prescribed fi res as a part of larger habitat goals to limit its density. "Some sources back East, where garlic mustard has been established for much longer, suggest that infestations go through a period of growing in dense patches but then begin to thin out with time," Lang said. "Some say garlic mustard becomes 'naturalized' rather than 'invasive' after a while, perhaps a decade or so. If garlic mustard does indeed thin out and allow space for native plants to once again grow in some reasonable level of plant diversity, then it is not a huge problem." However, land managers, including Lang, are hesitant to accept this observation as fact. It is unknown if the plant will do that in our region. "It is really hard to just let things go and hope that things turn out OK," Lang said. Studies on controlling garlic mustard are continually evolving, including a potential bio-control method. Canada has been testing several insect species with the hopes of combatting garlic mustard with a natural predator introduced from Europe. Agriculture and Agri-Food Canada has identifi ed the root mining weevil (Ceutorhynchus scrobicollis) as most promising. In August and December 2018, the Centre for Agriculture and Bioscience International released C. scrobicollis into the Canadian wilderness under close monitoring. Before release, CABI in Switzerland conducted years of safety testing, including under quarantine conditions at the University of Minnesota, to demonstrate that the species would eff ectively target garlic mustard without negatively aff ecting native species. "If the project is successful, it could be a very important addition to helping us manage garlic mustard infestations," Wood said. For the time being, Nebraska land managers remain vigilant. N Garlic mustard produces fl owers and seeds during the second year of growth.

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