Each plant has its own season to grow, reproduce and ultimately to die. This is true of the desirable plants, those that we so carefully cultivate in our gardens, and true of native plants that happily grow with only nature to care for them. It is also true of the non-native, undesirable plants (weeds) that we work so hard to remove from our landscapes. Working with the plants’ own life cycle and timing makes it easier to grow the desirable and remove the undesirable.
Plants (and weeds) can be annuals (going through their entire life cycle in a single year), biennials (requiring two seasons to complete that cycle), or perennials (with a lifecycle that can last several to hundreds of years).
Successful weed control is educated weed control. Identifying the plant, understanding its growth pattern, and targeting it when it is most vulnerable will translate into successful weed control. But first we have to understand some basics.
Annuals are the easiest to control and the least common of the truly noxious weeds because of that ease of control. Plucking them from the ground before seed is released or pulling them and properly disposing of the seed heads is all that is needed for control, and this task can be performed anytime. Locally, the most potentially serious annual weed is scentless chamomile, a pretty fern leafed, daisy-flowered escaped ornamental. Although not common here, it is very common in most mountain communities, spreading rapidly with its huge seed production – a single year’s seed can yield thousands of viable seeds per plant. Scentless chamomile has escaped from flowerbeds in Mountain Village, Ophir and Telluride, and has been found, in very small populations, on the Valley Floor and Lizard Head Pass. Herbicide control is seldom necessary unless populations are very large.
Biennial plants appear as rosettes in their first year. They increase in size and absorb nutrients throughout the season, then go dormant for the winter. In their second season, the plants bolt, producing flowers and seed. Locally common biennials include musk thistle, with large bright pink flowers and thorny bracts, and burdock, the large, sticky seeds often found stuck in your dog’s fur. Control of biennials is achieved by interfering with the plant’s flower and seed production by simply popping them out of the ground with a sharp shovel any time before seed production. If flowers are already present, removing them to the landfill or burning them is required. Locally, musk thistle can be found at Lawson Hill, on Hasting’s Mesa and in other areas throughout the region. Herbicide control may be required in large populations or in difficult to access areas.
Perennials are the toughest weeds to control, requiring early recognition and a deeper understanding of each plant. Some of the worst perennial weeds in the region are whitetop, Canada thistle, oxeye daisy and yellow toadflax, to name a few. Each plant has its own timing for control, with whitetop (or hoary cress) being the first in the group to deal with in the spring. All of the above reproduce not just by seed but also by creeping roots known as rhizomes. The target of control for these plants isn’t just the dense mat of plants above ground but also the 70 percent or more of the plant that exists below ground – often several feet deep.
Once allowed to become well established it is very difficult to remove these truly noxious weeds from the environment, but it’s not impossible. It should be noted that mowing these perennial invaders will often encourage more shoots, so this is a poor control unless combined with other methods. Similarly, digging or tilling can break off pieces of the roots that will then produce new shoots. Hand-pulling a few thistles or oxeyes cay be helpful, but once they have reached high densities – often as many as 30 or 40 plants per square yard or more – this control method is ineffective. These are the plants we target with much more intense treatments. Control methods with proven results include applying herbicides that are well timed and appropriate to the specific plant, and planting other species that are capable of competing with the invader.
Don’t let another season go by without recognizing the impact that undesirable species are having on your land and working towards their control. For assistance, identification, weed control planning and species-specific weed control recommendations, please contact your county weed manager. In Ouray County, contact Ron Mabry at 626-5391; in San Miguel County contact Sheila Grother at 327-0399; and in Montrose County contact Laurie Mingen at 249-5216. Both San Miguel and Montrose Counties offer cost share programs to encourage landowners to control noxious weeds.
Sheila Grother is Weed Control Program Manager for San Miguel County.