Aggressive weed needs aggressive response
July 3, 2008 · Updated 12:44 PM
"There are few weeds as ominous looking as the Canada thistle. With prickly spines jutting aggressively from its leaves and stem, the thistle looks like a villain from a Road Warrior movie.And just like such villains, its hard to kill.About the only good thing you can say about Canada thistle is that its not poisonous, said Gloria Wahlin, noxious weed coordinator for Island County. Wahlin said its important to get rid of the invasive plant when you see it or you will most certainly see a lot more of it.In fact, both the state and county make it mandatory for property owners to control it. That means pulling it, cutting it, covering it, spraying it, or feeding it to animals or bugs.These days, the thistle is easily seen in pastures, along roadsides and even in residential yards. Its purple flowers are one of the first things you notice. From a distance the cheery color actually makes the plant somewhat attractive.But Wahlin said the flower is getting ready to produce a pile of seeds that will soon be carried by the wind to other locations. Meanwhile, below ground the plant is spreading its huge root system out as much as 19 feet horizontally and up to 22 feet straight down. As a result, one plant can quickly become a colony.What to do?The best way to control the weed is to mow it repeatedly either by hand or with a large mower or string trimmer.Of course you have the added labor of gathering up the cuttings if you think the thistle heads are developed enough to set seeds, said Wahlin.Its best to start mowing around mid May and keep cutting it down all season. But if youre getting a late start like a lot of people, theres still time to whack on it before it goes to seed. Just remember to pick up what you cut down. The seed heads can still ripen and spread seed even lying on the ground.Thistle can also be controlled by pulling it, but its important not to till the ground afterward or you may spread parts of the stem that can resprout. After pulling, cover the ground with heavy plastic, wood, carpet or other material water cant get through and leave it in place for at least two years. Thats right, two years thistle is a pretty mean weed, to be sure.Chemicals marketed under the names Curtail and Stinger are effective against Canada thistle and are approved by the Pacific Northwest Weed Control handbook published by Washington State and Oregon State universities. But, as with any chemical, its important to read the instructions carefully to make sure youre not harming other parts of the environment. Its also advisable not to use chemicals around crops.Another organic method to control the weed is to use goats or donkeys, which find thistle a gourmet delight. But Wahlin said you have to be careful about using goats for control, because the animals also like to eat many other plants and can do more harm than good to a garden space.You can also use certain types of bugs, such as the Canada thistle bud weevil, the stem weevil or the thistle stem gall-fly, all of which weaken or strategically damage the plant.County officials have already released such thistle-eating insects throughout the island in hopes they will provide much-needed natural control of the non-native weed.Canada thistle often grows alongside the equally nasty-looking bull thistle which has a larger flower head and more spines. But bull thistle is a biennial plant that dies after it flowers. Canada thistle keeps right on growing.If you have Canada thistle growing on your property and want more information, call call Wahlin at 679-7327 or 321-5111, extension 7211. Its also a good idea to look for the weed on neighboring property. Knowing the thistles aggressive tendencies, its likely headed your way."