Irene Shonle, Director CSU Extension Gilpin County.  Noxious weeds are rarely anyone’s favorite subject, but it is so important to control them in order to preserve the native plants and ecosystems around us. Noxious weeds are non-native plants that are known to cause environmental or agricultural damage, and it is everyones responsibility to control them.

To win the war on weeds, it is helpful to organize your attack based on the life cycle of the weed. Some weeds only live for the summer and then go to seed in the fall (these are called annuals). State-listed noxious weeds that are in this category are cheat grass and scentless chamomile, and nuisance weeds are small-flowered alyssum, field pennycress, shepherd’s purse, and lambsquarters. Because they only spread by seed, the key to controlling these weeds is to keep them from going to seed.  You can do this by hoeing/pulling them early, before they even flower (this has the advantage of no disposal issue), or pulling, bagging, and tossing them if they already have set seed.  If you are so inclined, you could also try an herbicide, but the annuals need to be small and growing for this to be effective.  If they’ve already set seed, it will probably be too late – pull and bag them, and go after them earlier next year.  Keep this up for a few years, and when all the seeds that are dormant in the soil are depleted, you will be weed free!  Planting grass seed or wildflower seed to cover the bare ground is also helpful – weeds love to colonize bare, disturbed soil.

Biennial weeds are very similar to annual weeds, except they take two years to go to seed (and then they die). The good news is that you have two years to deal with an individual plant. The bad news is that a biennial weed can be much larger, and can produce more seeds (a musk thistle, for example, can produce over 100, 000 seeds before it dies).  Biennial weed control is the same as for annual weed – dealing with them before they flower is highly recommended because of their size and the related disposal issues.  Biennial weeds in this area are diffuse knapweed, musk thistle, mullein, spotted knapweed, and dame’s rocket (sweet rocket).

Perennial weeds are more challenging to deal with. These tricky plants come back to haunt you every year --  so not only do you have to worry about the seeds they produce, but you have to get rid of the individual plant. In some cases, pulling or digging perennial weeds may work – especially when the plant is a tap-rooted perennial (like a dandelion). The more of the root you can get, the more likely it is that you will kill the weed.  Creeping perennials -- the weeds that spread underground by horizontal roots called rhizomes – are the most difficult of all.   Unless you are prepared to pull them on a weekly or semi-weekly basis, a systemic herbicide may be the answer. This is because their extensive root system makes it easy for them to recover and send up new shoots, and it takes a lot to exhaust the root reserves. A systemic herbicide will kill the entire plant because the chemical is translocated from the leaf of the plant down to the root system.  Perennial weeds around here are oxeye daisy, canada thistle, leafy spurge, chinese clematis, common tansy, whitetop (hoary cress) and yellow toadflax.  All of these are creeping perennials except the clematis. As with the annuals and biennials, reseed the area with grasses or flowers to provide some competition.

Gilpin County residents:  take advantage of the weed-spray check out program for noxious weed control.  You can check out a low-toxicity herbicide called Milestone (good for thistles and knapweeds) for free from the Extension office. If you need help in identifying your weeds, or would like more information, call or stop by the Extension Office – bring in samples of your weeds!

The CSU Gilpin County Extension Office is located at the Exhibit Barn, 230 Norton Drive, Black Hawk, CO 80422, 303-582-9106, www.gilpin.extension.colostate.edu. Colorado State University Extension provides unbiased, research-based information about, horticulture, natural resources, and 4-H youth development. Colorado State University Extension is dedicated to serving all people on an equal and nondiscriminatory basis.