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THE BRUCE TRAIL CONSERVANCY |
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Garlic Mustard Control |
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Bruce Trail Conservancy Environment Committee |
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Environment Committee |
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“Controlling garlic mustard,” according to my wife Franca De Angelis “is an urgent matter for the Bruce Trail Conservancy.” Franca, who has hiked the Bruce Trail twice, was speaking at the annual general meeting of the Caledon Hills Bruce Trail Club on Sunday, April 6th. According to her, garlic mustard is threatening native woodland flowers and may even be retarding the development of Ontario hardwood forests. Because hikers are likely spreading the garlic mustard seeds, this gives Bruce Trail members a particular interest in the subject. |
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Franca and I first became aware of garlic mustard on a geological hike with Beth Kümmling in 2004. We were tramping through the Pretty River Valley, listening to Beth describe a long-since drained glacial lake, when one of the budding geologists on the hike said: “Oh, look at all the garlic mustard.” Not knowing much about it, but being told that it out-competes native wild flowers like trilliums; we happily started helping pull the plants from the forest floor. So much for Beth’s glacial lake! We didn’t think much more about garlic mustard until, about three years ago, it first started appearing in the Hockley Valley, our home turf. Interestingly, its first appearance was along the edges of the Bruce Trail or at places where hikers parked their cars. Does this give a clue as to how it is spread? It appears that the seeds attach themselves to hiker’s boots or possibly their clothes – and, perhaps, the fur of the dogs that hikers sometimes have with them – and then fall off at other locations. However garlic mustard is spread, when it first appeared in the Hockley Valley, Franca became concerned. One of the first things she did was attend a Bruce Trail land stewardship meeting in Owen Sound where she listened to Hamish Duthie talk about garlic |
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First Year Plant |
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Second Year Plant |
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mustard and ways to control it. Hamish is on the Bruce Trail Conservancy’s Environment Committee. She also contacted the Royal Botanical Gardens in Hamilton, one of the few organizations that have a garlic mustard management program in place. The Bruce Trail traverses its property. Garlic mustard is an invasive species, originally brought to North American from Europe. It was brought over, it is thought, because Europeans were accustomed to using it as a herb in medicines and in such things as salads. It can also be used to make pesto. The first record of it in North America is in 1868 in Long Island, New York. It now is common in the forests of many states and, unfortunately, Ontario. The problem with it is that it has no natural enemies in North America – insects, animals or parasites – so it grows unchecked. And, as it grows, it out-competes native forest plants by monopolizing light, moisture, nutrients, soil and space. Anyone who enjoys a hike in the woods in the spring, admiring the trilliums, spring beauties and Dutchman’s breeches, should be worried. Garlic mustard will replace these flowers. And if you doubt that, take a hike along the Bruce Trail through St.Catharines to see what a menace garlic mustard has become. |
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Garlic mustard reproduces only by seed. Most seeds germinate within the first or second year after being produced but can remain viable in the soil for up to five years. Seeds germinate in the spring and form low growing rosettes of dark purple to green, kidney-shaped leaves with scalloped edges. Young leaves smell of garlic or onion when crushed, although the odour becomes less intense as plants grow older. Research conducted in 2006 suggested that garlic mustard harms fungi that native forest trees need for proper growth, hence the worry that the spread of garlic mustard may retard the growth of native tree species. Lisa Gross1 described the problem as follows: “Many forest trees and other vascular plants form mutually beneficial relationships with arbuscular mycorrhizal fungi (AMF). The fungus has long filaments that penetrate the roots of plants (forming branched structures called arbuscules) and snake through the soil in an intricate interwoven network of mycelium, which effectively extends the plant's root system. AMF depend on the plant for energy, and the plant depends on the fungus for nutrients. Many non-native plants, including garlic mustard, do not depend on native AMF and often take root in landscapes |
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altered by development or logging, where AMF networks are disturbed. When these non-mycotrophic invasives propagate, they may diminish AMF densities even further. Biologists are especially concerned about what might happen if a non-mycorrhizal invasive plant turns up in a mature, intact forest with an established mycelial network—which is just what garlic mustard has started to do. In the North American forests it has recently invaded, the plant inhibits the growth of understory plants, including the seedlings of canopy trees. Stinson et al. suspected the invader might somehow be thwarting the symbiotic relationship between fungus and tree.” Management strategies for controlling garlic mustard are varied– a lot depends on the location and the characteristics of a particular patch. For two sections of the Bruce Trail in the Hockley Valley – the section immediately south of Dunby Road and the section on the south side of the valley between the 3rd and 4th lines of Mono – Franca and Fred are leading teams of volunteers on May 13th who will pull the second-year plants and bag them in black garbage bags. To make sure the seeds are killed, these bags will be sealed and left in the sun for several weeks – effectively ‘stewing’ the vegetation inside. A better strategy would be to burn the plants but this requires a burn location and plenty of combustible material, something that is not always available. Whether the second-year plants are bagged or burned, some argue that this is a useless exercise as, in disturbing the soil, the remaining seeds are only encourage to germinate. Garlic mustard seeds tend to only germinate, or germinate particularly well, in disturbed soil. That is why some groups suggest that a better strategy is to simply cut the flowers off the garlic mustard plants and take these flowers out of the woods. The Nature Conservancy of Canada is organizing a group of volunteers to cut garlic mustard flowers this spring in a wood lot near King City, Ontario. Another control strategy, if people can get out early enough in the spring (late April and early May), is simply to pull the first-year plants (or second-years plants before they flower) and leave them on the forest floor. There are no seeds on these plants so there is no danger of spreading the problem. Care, however, must be taken because the first-year plants can be mistaken for other plants: toothworts (Dentaria), sweet cicely (Osmorhiza claytonii), and early saxifrage (Saxifraga virginica). That is why a safer strategy may be to concentrate on the second-year plants: the flowers are immediately recognizable. Other strategies include weed-whacking or the use of a lawn mower (where the terrain permits). This may work where the patch of garlic mustard is so thick that pulling is just not feasible. But, because a garlic mustard plant will sprout multiple shoots from its roots, these strategies are best done where repeated efforts can be made throughout the spring and early summer. In extreme cases, it may also be necessary to consider spraying garlic mustard. Hamish Duthie has suggested using agricultural vinegar - horticultural vinegar and yucca - as this is environmentally friendly. He says this has been successful when used on the small, first-year plants. However, this approach might not be successful if used to treat older plants. Rick Grillmayer, the forester at the Nottawasaga Valley Conservation Authority (NVCA), reports that a consultant he knows tried both acetic acid and agricultural vinegar (+ yucca) on garlic mustard. All this did was burn the leaves, leaving the plants to recover and re-spout. Rick thinks a systemic herbicide glyphosate (e.g., Roundup®) may be used as a methods of last resort. In fact he is investigating an applicator that does not involve spraying – it’s a device that simply sponges the herbicide on the leaves of the plant, leaving the plant to draw the herbicide down to the roots. Since garlic mustard is taller than most surrounding plants, this might be an effective way of killing only the garlic mustard and leaving the other plants safe. In the meantime, though, the NVCA is using volunteer staff time to pull the weed on its properties – two of these properties have the Bruce Trail running through them. At the CHBTA annual general meeting, Franca also reported that some research is being done with biological control. “At the University of Michigan, insects (weevils) with garlic mustard specificity are being tested and, from an experiment carried out on a degraded woodlot in the vicinity of Waterloo, it has been suggested that the presence of bloodroot may mitigate the spreading of garlic mustard.” The Nature Conservancy of Canada is leading a group of volunteers in May to pick garlic mustard flowers in the Happy Valley near King City. With the flowers picked, obviously, no seeds will be produced. But for Franca, the first step in the control strategy for the Bruce Trail should lie with the Trail Captains. “They are our eyes,” she explains, “and whatever else we do, the first thing we need is an accurate inventory of where garlic mustard is growing.” To this end, she is working with Colleen Darrell, the CHBTA Trail Co-ordinator, to contact and educate all CHBTA trail captains. “Then,” she continues, “it’s on to the other eight clubs.” As she explains, garlic mustard is particularly bad in the Niagara and the Blue Mountain sections. “There is only one tiny patch that we have seen in Dufferin Hi-lands,” Franca says, “and we only saw one small patch in the Peninsula Section (just north of Lions Head). It’s important to concentrate on these first outbreaks,” she continues, “so the problem can be contained before it gets out of control.” Fred Nix April 20, 2008 Article from the Caledon Comment, summer 2008 1 A “Wick Weeder Herbicide Applicator” sold by Rittenhouse --- www.rittenhouse.ca, |
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This article includes an excellent description of a problem the Bruce Trail is experiencing due to the non-native invasive plant garlic mustard. Attempts are being made to remove and/or control the plant along the Bruce Trail. The selected technique of removal of garlic mustard largely depends on the density of the plants, the size of the area the plants cover, how long the plants have persisted in the area, and the level of commitment by those participating in garlic mustard removal. This article refers to pulling of garlic mustard as one option of removal. This should not be attempted without prior knowledge of the first occurrence of the plant and without willingness for long term (5+ years) commitment to removal and monitoring. Garlic mustard produces seed pods in mid/late summer with each plant producing hundreds of seeds that can be scattered several meters from the parent plant. The seeds can be viable for up to five years in the ground therefore pulling will disturb the soil and allow the huge seed bank to germinate replacing the single parent with dozens of offspring. Plants that have been established for more than one year may have already dispersed hundreds of seeds that may establish once the soil is disturbed due to pulling. That is why other methods may be more suitable unless those removing the plant are prepared for annual removal and monitoring for five or more years. In order to determine which method is most suitable for the removal and control of garlic mustard please consult an ecologist or e-mail the environment committee for more assistance at mail@BTCenvironmentcommittee.org prior to attempting to remove garlic mustard along the trail.—Sal Spitale—BTC Environment Committee |
