Spotted Knapweed and Other Invasive Species
or Out, Damn’d Spot(ted)! Out!
By Moralea Milne Nov 9, 2007
For many of us, fall means innumerable soccer practices and endless hours ferrying our children from one activity to another. For others, cooler weather and shortening days creates the incentive to travel, to seek out warmer and drier climes.
To some of us involved in environmental do-goodism, it is a time for duty. The autumn rains soften the summer baked concrete soils, signaling that it is time to head to Devonian Park or other areas that are rife with invasive species and begin again the Herculean task of rescuing our flora and fauna from the death grip of introduced, invasive species.
Invasive species, alien invaders, dog-gone weeds! Almost more than development and land use changes, they tear at the resolve of environmentalists everywhere. Insidiously they show up, skulking about for years before they seemingly leap out of the blue and claim their territory, decimating meadows, woodlands and wetlands alike. There is an invasive specie for every situation.
Walk through East Sooke Park or parts of Witty’s Lagoon and find the forest floor overrun with that rhodo wannabe, spurge laurel (aka daphne) and that creeping, climbing, suffocating, green menace-English ivy. Meadows that were once clothed in blue camas are now defiantly yellow with broom and gorse. Wetlands throughout the continent have come under ferocious attack by that siren, purple loosestrife, some has recently been spotted in Metchosin. There are bloated bullfrogs, copulating rabbits, raucous flocks of omnipresent starlings and literally millions of proliferating black licorice slugs. There are relatively new weeds like spotted knapweed, tansy ragwort and spartina as well as the older foes like broom, gorse and hedgehog dogtail (grass).
Without too much difficulty you can get me to rant on interminably about introduced, invasive species, no doubt ensuring some eye-rolling and probably causing some people to duck when they see me coming! Why all the furor?
Introduced, invasive species are organisms that have, through no fault of their own, arrived in a new landscape. A landscape that is conducive to their growth and reproductive success and one that does not include any naturally occurring forces that could provide some restraint on their burgeoning populations. Meaning perfect growing conditions and no predators of consequence.
New plants and animals-wouldn’t that add to biodiversity-the buzzword of the times? Unfortunately what happens is that the new organisms, be they of the air, earth or water, act like kids in a candy store. With no natural limits (parents or shopkeeper) they multiply at such a rate that they outcompete the existing flora and fauna (decimate the candy store). They muscle out the highly adapted native species. Instead of a meadow with thousands of plants and dozens of species, you have an impoverished site, a grassland with a only few species and most of these not recognized by the local insects, birds and animals as being edible or supplying habitat values. Adding insult to injury, these newcomers often come equipped with the ability to change their surroundings to be more to their liking. Some release poisons that stop plants from germinating, giving themselves more space to grow; some change the soil components so that there might be more nitrogen, making it harder for plants adapted to poor soils to survive; some use up all available moisture; some, like the introduced grey squirrel, use up the available nesting sites and eat the young of other species.
How do they get here?
They come in a variety of ways. Homesick for the old country? Bring over a few of your favourite species to make you feel more at home in your new landscape, that’s what happened with broom and starlings. Sometimes they arrive inadvertently in a shipment of agricultural seeds (knapweed); sometimes they hitch-hike a ride on a passing ship (rats); or in the ballast water picked up in one port and jettisoned in another (zebra mussels). Sometimes we invite them in, thinking they will take care of a problem (cane toads in Australia or English sparrows which were first imported to help fight agricultural insect pests, although they are primarily grain and seed eaters!) or they come by accident in nursery stock (many pathogens such as Chestnut blight, Dutch elm disease and black licorice slugs). Sometimes the nursery stock itself is to blame, English ivy is used extensively in landscaping and purple loosestrife is a beautiful garden ornamental.
There has been a slight shift in the thinking of those professionals entrusted with the task of designing management strategies to tackle invasive species. While not abandoning the battle to control more established weeds like broom, gorse and ivy, there is now an effort afoot to recognize new invasive plants (and animals!) before they become an entrenched problem. The expectation is that if we can identify and deal with an invasive introduction while it is a relative newcomer, it will be easier to control or even eradicate.
One of our newest invasive species is spotted knapweed. Only a few years ago there were a handful of plants along the road by the gravel pit and at the entrance to Tower Point. Unfortunately no one recognized the danger in time and the large field in the park is now chock-a-bloc full of the weed. If you have ever traveled to the southern interior you will know what a huge problem this can become. There, knapweed is universally hated as it invades pasture and crown land grazing areas, reducing them to knapweed deserts, unfit for livestock or deer and elk. Knapweed is a displaced member of the aster family and one of the plants which secrete a toxin that prevents other plants from growing in the area around them.
At a casual glance it looks somewhat like a smaller variety of thistle and it has a stiff, thistle-like flowerhead, usually purple, with narrow, divided leaves, the layered bracts surrounding the flower are tipped with a triangular black spot-hence its name. Flowering from July till October, it is capable of producing 400 seeds per plant in its normal, dry, growing conditions and up to 25,000 seeds under irrigation! It is a strong competitor on disturbed lands but can also invade natural landscapes.
The most effective and least time consuming way to handle invasive species is to prevent their establishment. Promote healthy native plant communities, disturb soil as little as possible and learn to recognize these alien invaders. Once an infestation is found, a control strategy should be mapped out. Decide where to spend your energy to get the greatest returns. Generally it is recommended to deal with the smallest areas of new invasions on the least disturbed sites, working towards the largest infestations on the most disturbed areas. It is crucial to success to limit new seed production and to deplete the seed bank.
In the case of spotted knapweed, it may be hand pulled, usually three times a year. Once, while the soil is still moist and pulling can remove the taproot; secondly, after the remaining plants have bolted (they form ground hugging rosettes-somewhat resembling dock- that will send up a flowering stalk)-usually in late June; and thirdly before seeds are dispersed. Mowing and cutting can be somewhat effective and should be carried out in the early flower stage; plants are less likely to resprout if allowed to bolt before cutting. Cutting must be repeated over several years to deplete the seedbank. If you are interested in using a chemical solution, non-selective herbicides will need repeat applications (a wipe-on application of Round-up is recommended) but first consult an accredited professional for advice. New plants will germinate, so remember to keep visiting the site and remove of any newly emerging or resprouting plants.
Other new invasive plant species are: carpet burweed, orange hawkweed, giant and Japanese knotweeds, dalmation toadflax, yellow flag iris, giant hogweed and butterfly weed. Contact the Coastal Invasive Plant Committee for more information at email@example.com or 857-4272.
Too numerous and too successful and sometimes it seems, on a particularly disheartening day, too impossible to even contemplate controlling. However, some Sunday mornings during the winter months, we manage to have some fun and share good times at Devonian Regional Park as we continue our “duty” at the park. It will be seven years this season that we have been involved in removing broom from the park and we are making a difference. If you would like to join us, contact Moralea at 478-3838 or firstname.lastname@example.org.
Monday, October 13, 2008
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