Weed comes in many different varieties, but we are not here to discuss that. We are here to discuss noxious weeds.
Weeds are by definition a plant that is considered undesirable in the location it is growing, ie. your garden bed. Most of us consider dandelions to be a weed, and that is mostly because they have way of growing everywhere! In the spring they are great food for bees waking up from their long winter’s nap, but that is a whole other topic. Dandelions are not considered a noxious weed even though they are quite annoying to deal with. A noxious weed is a non-native invasive species that invades and takes over native plants. A few of the more noticeable ones are the musk thistle, canada thistle, myrtle spurge, Russian knapweed and oxeye daisy. Let’s take a moment to learn a little about these pesky plants.
Those large purple flowers may seem pretty from afar but this plant has a way of taking over entire native areas. The musk thistle is pretty unique in that it is biennial. That means that in its first year of growth it is only a rosette, a small plant that doesn’t flower. The second year is when it causes all the problems because, that is when it grows up to 6ft tall and produces flowers. Another pretty cool thing about the musk thistle is that once it flowers, the plant dies and won’t regrow. However, the reproduction of this plant is solely by seed, and each plant can produce up to 20,000 seeds! Because of the style of this plant it requires a unique eradication method. If we can treat it during the rosette stage we can use a broadleaf herbicide to kill it or you can hand dig the plant out. If we can catch them before they have flowered we can also use an herbicide that will prevent viable seed development. But once the plant has flowered the only way to treat it is to cut off the flower heads and put them in a bag so the seeds will not spread. This plant will still go to seed even after the flower head has been cut, so proper disposal is a must. This noxious weed is on the B list through the state and we are required to do our part to stop the spread of them.
OH Canada, why did you give us this thistle? Just kidding, this thistle comes from Europe(via Canada). You can find this weed all throughout the county as well. The flowers are much smaller than that of the musk thistle and unlike the musk thistle this one is a perennial. That means the same plant will come back year after year, getting stronger and stronger every year. This pesky Canada thistle propagates in multiple different ways making it a lot harder to control than the musk thistle. Aside from it coming back every year it also sends out rhizomes (root suckers) underground to form new plants, as well as each plant can produce around 1,500 seeds! Because of its extensive root system hand pulling this weed will only encourage the weed to sprout and grow more. The best ways to manage the spread of this weed are to prevent it from flowering and to cause the plant consistent stress. The stress can come in the form of mowing operations or by having a strong healthy garden/native area that doesn’t have bare unhealthy areas. Once infestation has occurred herbicides can be used to assist in getting rid of this thistle. Because it is a perennial, the herbicide treatment has to be done in the fall when the plant is sending its nutrients down into the roots or in early spring when it is craving nutrients. Once it has flowered it is best to cut the flower heads to prevent seed spread and wait until fall to apply an herbicide. Canada thistle is also on the state B list, so if you have it in your yard it is your responsibility to have a management plan. That management plan could be making gin like Burichladdich does in Scotland!
POISONOUS!!!! This is a very invasive ornamental plant that is also very poisonous. Myrtle spurge was also brought over from the motherland of Europe as an ornamental plant and has just gone buckwild in some parts of the country. It is a really uniquely cool plant from the succulent family, so it is a shame it is so invasive as well as poisonous. Myrtle spurge propagates by root and seed; it can actually throw seeds up to 15 feet away! The seed pods explode, in a way, and send the seeds flying. This weed is on the A list for Colorado, so that means it needs to be eliminated completely. Now, because they are poisonous you want to make sure you are protected when removing them. Proper protective attire is gloves, long sleeves, pants and close toed shoes.The milky sap that is released when a stem is broken can cause severe irritation to eyes and skin. If ingested it could cause nausea, vomiting and diarrhea. The best ways to control and rid your lawns and garden of this plant are to dig it up, ensuring that you get the whole tap root, and to use herbicide treatment in spring or fall.
Russian knapweed is easily confused with the Canada thistle. It is also a perennial like the thistle and can propagate by rhizomes or seed. Russian knapweed has an evil side to it. This plant is what they call allopathic, meaning it sends out toxins to nearby plants that inhibits their growth! This knapweed has the same mitigation method as the Canada thistle, stress it out to minimize rhizome spread, and use herbicides. You don’t want to hand pull these guys either because that will encourage growth. It is best to treat them in the fall with an herbicide. These are also on the B list for Colorado, so a management plan needs to be put into place.
For some reason I have a personal vendetta against oxeye daisy. I can’t really explain it, but I just want it gone! It might have something do with the fact that the other weeds listed above are quite easily distinguishable as a noxious weeds, but the oxeye daisy looks like a beautiful wildflower. They are very pretty, but they are very invasive and can take over entire mountain meadows pushing out the actual native wildflowers. Oxeye daisy looks very similar to a non-invasive shasta daisy, so they are easily confused. The shasta daisy is about 6-12 in larger than the oxeye daisy. They too are a perennial and will come back year after year. They mainly spread from the roots and one flower can have around 200 seeds! They do have a shallow root system so they are easier to hand pull, but be careful because when the roots are not pulled deep enough it could just encourage growth. If you cut the flowers, be sure to bag them because they will still go to seed after being removed from the plant. Herbicides can be used to help mitigate infestations as well.
Now that you know a little more, maybe more than you wanted to know, about noxious weeds, take a look at your garden and see if treatments need to be done. All the information used to put this informative blog together was found on the Colorado Department of Agriculture website and is easily accessible to anyone who wishes to learn more. I hope I have piqued your interest and that you’ll take a look at all the other noxious weeds that plague our beautiful Colorado landscapes. If you have any questions about the plants in your garden, give us a call and we can come inspect it and identify it for you. If it is a noxious weed we would be more than happy to smoke it for you. 😉