There are weeds, and then, there are noxious weeds. Just what is a “noxious weed?” These are plants that are listed on the Colorado Noxious Weeds List. They have been identified as being a threat to native species, usually because they are incredibly invasive. The list is divided into three sublists: lists A, B, and C. If a plant is on List A – it has been identified as a threat that is still possible to be contained and eradicated. We are legally required to eradicate these species if they show up on our property. An example of one that has shown up in residential landscapes in our area is myrtle spurge (Euphorbia myrsinites). List B species are generally too established to hope for eradication. Instead we try to contain them and stop their further spread. If you’re familiar with the plant called “butter and eggs” (Linaria vulgaris) then you’ve seen a List B plant. And List C plants are the ones that I joke are just too far gone – they’ve gotten too established and are too aggressive to eradicate and, possibly, to even contain. (Got bindweed (Convulvulus arvensis)? Then you have a List C noxious weed.)

You can see all of the plants on the Colorado Noxious Weeds List here:
(Be patient – at first it will seem that only the top banner has loaded, but the rest will load after a little bit.)

Monument Valley Park in Colorado Springs has a fair number of plants listed on the Colorado Noxious Weeds List. Here are some that I have seen:
List C – Chicory (Cichorium intybus), Common burdock (Arctium minus), Common mullein (Verbascum thapsis), Downy brome (Bromus tectorum), Field bindweed (Convulvulus arvensis), Perennial sowthistle (Sonchus arvensis), Puncturevine (Tribulus terrestris), and Redstem filaree (Erodium cicutarium)
List B – Bouncing bet (Saponaria officinalis), Canada thistle (Cirsium arvense) , Dalmation toadflax (Linaria dalmatica & genistifolia), Musk thistle (Carduus nutans), Russian olive (Elaeagnus angustifolia), Salt cedar/Tamarisk (Tamarix chinensis, T. parviflora, and T. ramosissima)
List A – Purple loosestrife (Lythrum salicaria)

Funding for Colorado Springs city parks has been pretty dismal (or worse) over the past few years, and the city does not have a weed management office. So control of these weeds has not been a high priority. However there two that I felt really needed to be given attention when I noticed them in the park, tamarisk and purple loosestrife.


Full grown tamarisk (blooming white)

I first noticed tamarisk growing in the park a few years ago. It’s a shrub that can grow to 20 feet tall! (I’ve seen some about that tall along Fountain Creek at Fountain Creek Nature Center.) They are famously known for lining the edges of streams or rivers until they are just about the only species. Each plant can produce up to 600,000 seeds every year that it blooms! They germinate fairly easily in the moist soil of the streambanks, so populations grow rapidly.

In the park, the first one I saw was in the northern part of the park. It was actually on higher ground, away from Monument Creek. I reported it anyway, and it was cut down several weeks later. Then last year, I noticed new growth from the stumps of that same plant. Additionally, new plants appeared in three other places – two of them right on the creek’s edge (one in the northern part of the park, the other in the southern part). I reported them to Colorado Springs Parks and Recreation late last summer and then reported the plants again to them and Colorado Springs City Forestry this summer. Within a week, City Forestry took care of the two clumps by the creek’s edge, and I met with them to point out the original one growing away from the creek. They treated the stumps with an approved herbicide, but the recent heavy rains may have diluted the effectiveness. Tamarisk is “only” a List B species, but given that these were the first I’d seen, I hoped it might still be possible to eradicate them from the park.

City Forestry cutting down and treating tamarisk clump

City Forestry cutting down and treating tamarisk clump


Purple loosestrife on bank of Monument Creek

Purple Loosestrife
A few weeks ago, I was jogging along one of the park trails when a splash of bright magenta purple by the edge of Monument Creek stopped me in my tracks.  I thought, “It couldn’t be purple loosestrife…..could it?”. I’d never seen a List A species in the park, but I took a detour down by the creek to check it out. Sure enough, it was the beautiful purple loosestrife. (This beauty is one of the plants on the CO Noxious Weed List that came in as a European introduction for gardens in North America. )

As a List A plant, I knew that someone was required to eradicate it. I reported it immediately using the GoRequest app on my phone (an app that lets you report things directly to city government with GPS coordinates, photos, etc). In nearly August,  City Forestry and Parks and Recreation coordinated to cut down and treat the plant with an approved herbicide.

Why is this plant such a problem? A mature plant can produce up to three million seeds per year, so it doesn’t take long to build up a huge seedbank in the soil, and some of the seeds will travel in the water to points downstream. These seeds can remain viable for up to 20 years, so we’ll have to keep this site monitored to see if any seeds were produced and dropped this year or possibly even in previous years.