As weed management professionals, one of the biggest mistakes we see people make is incorrectly timed management.
Controlling weeds is already an uphill battle, so ensuring you are doing the right things at the right time is paramount to success.
Proper identification of the target plant is the first step in any weed management plan. Once you have an ID, you can start to fill in crucial blanks about its biology, particularly its reproductive and growth cycles. Knowing this information will get you headed in the right direction for management timing.
For plants that only reproduce by seed, like most annuals, biennials and simple perennials, effective management methods need to be implemented before the plants disperse seed for the next generation. Better yet, do it before they even form flowerheads to reduce the chances of viable seed being left behind to germinate. There will, of course, be seeds left in the soil seed bank from previous years that may germinate for several growing seasons. However, once the reproductive cycle of the target plant is continuously interrupted, the seed bank will deplete itself in time.
The time of year a target species emerges and when they form seeds are key pieces of information that indicate when management practices should begin.
Winter annuals are some of the first plants to emerge in springtime and usually go to seed by early summer. They would need to be managed far sooner than later-emerging species that may only just be breaking ground while winter annuals are seeding out. Though it may seem obvious, one needs to know when a plant will be around to do anything about stopping its spread.
In some cases, there are even more specific timing windows to be aware of.
For example, the herbicide-resistant annual weed kochia needs to be targeted while they are young seedlings and are more susceptible to the effects of herbicides. While kochia can still be pulled or mowed before it sets seed, herbicides lose their effectiveness long before the plant forms flowers. Biennial species, which spend their first year as a rosette then bolt and flower their second year, are more easily controlled their first year in the rosette stage. Though management is still effective in the second year, it’s better to nip them in bud, so to speak.
Things get trickier with the complex perennial species that can reproduce by rhizomes that spread underground through the soil. These plants don’t necessarily rely on seeds to reproduce, though new populations are formed by various means of seed dispersal. Established plants send out creeping roots that form new sprouts above ground, creating dense patches and monocultures. These root systems overwinter, then plants resprout in the springtime and continue their spread. Mechanical removal methods are often futile on these deep-rooted plants, meaning herbicides or biological controls are the best bet.
Herbicide applications on these species should be done initially when the plants are flowering. Before this point, the upward flow of the nutrients from the roots will push out the herbicide, killing the top portion of the plants but leaving the roots intact. When the plants are flowering, the circulatory flow is such that it will allow the herbicides to be absorbed into the roots, killing the root system more effectively.
A better time to treat these perennials, though, especially a well-established stubborn patch, is in the fall. They will begin to send nutrients into their root systems to overwinter as the first frost approaches. Applying herbicides in this window will result in the plants absorbing the herbicide into their roots, dealing a deadly blow. Population densities are often drastically reduced the following year after a fall herbicide application.
The more you know about the target plant, the more obvious the timing of the treatment will be and the better the management results will be.
There are a plethora of resources available for plant identification from online apps like iNaturalist to old-school field ID books to help you properly identify your target plant. The Archuleta County Weed and Pest website has fact sheets on the noxious weeds found in our county, which have helpful identification tips and management strategies.
If ever in doubt, contact local experts at Colorado State University (CSU) Extension or the Archuleta County Weed and Pest Department to help you. We are a free educational resource and are here to help you become better stewards of your land.
Yellow alyssum
After two back-to-back dry winters, yellow alyssum, also known as pale madwort, has emerged in mass.
This plant belongs to the mustard family and is an annual, meaning that it germinates, flowers, produces seeds and dies in a single growing season.
Due to our March warming spell, it emerged early and has taken advantage of the dormancy period of our native plants. It is considered a weak invader, and cultural controls such as rotational grazing, replanting with natives and minimizing soil disturbance can reduce its foothold or prevent its invasion. During dry years it is more prevalent as its early emergence allows it to capitalize on what little moisture was in the soil.
Yellow alyssum can be managed with herbicides early in the year from the rosette to flower stage, but once the round seed heads start to form below the uppermost blooms, mechanical control is a better option.
Mowing at the full flower stage can prevent seed production, but once seeds are formed it is best to hand-pull and bag plants to reduce the soil seed bank the next year.
When the plants become brittle and the seed heads start sticking to your socks, it may be easier to grab a painters pole and a roller and pick up the seeds that way.
If our monsoons shape up nicely this year, our native species will rebound and be able to crowd out the spaces where we are seeing yellow alyssum this spring. Overseeding can also help in degraded areas— if we get enough moisture to trigger germination.
Archuleta County Weed and Pest is your local resource for managing noxious weed populations and controlling other pests.
Bioblitz
Save the date for Archuleta County’s first annual Bioblitz: June 20 from 8 a.m. to 8 p.m.
Join us for a day exploring the natural areas along the San Juan Riverwalk and Reservoir Hill while collecting valuable ecological information.
This is a fantastic opportunity to connect with nature and appreciate the vibrant life that thrives in this ecosystem.
No prior experience is necessary, just bring your curiosity and enthusiasm for nature.
The cost is $25 per adult and $10 per student/child, includes dinner, a T-shirt and a fun day of learning.
To learn more and to register, visit https://secure.rec1.com/CO/pagosa-springs-co/catalog?filter=c2VhcmNoPTQyNjMyMzY= or email Galabota at cindi.galabota@colostate.edu.
Volunteer for the Archuleta County Fair
Be a part of preserving the rich heritage and timeless tradition of the Archuleta County Fair and help plan the 75th anniversary Fair in 2026.
You’ll contribute to an annual tradition that brings our community together, supports local agriculture and creates lasting memories for generations to come.
To learn more, contact Tonya Steadmon at tsteadmon@archuletacounty.gov or (970) 264-5931.
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