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Noxious Weeds

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  • Noxious Weed Classification
  • A Few Notes about Noxious Weeds
  • Noxious Weed Guides
  • Organic vs Inorganic Herbicides
  • 9 Keys to Successful Seeding
  • Why Did My Grass Not Grow?

Noxious weeds, as defined in the Colorado Noxious Weed Act, are non-native “alien” plants that aggressively invade; are detrimental to economic crops or native plant communities; are carriers of detrimental insects, diseases, or parasites; or have direct or indirect effects that negatively impact the environmentally sound management of a natural or agricultural ecosystem. Noxious weeds come in all shapes, sizes, and colors. There are over 30 species of state-classified noxious weeds in Middle Park. Some are cute, some are spiky, and many would be considered “beautiful” by anyone unfamiliar with their ugly and vicious side.

Noxious weed seeds can spread by wind, water, birds, wildlife, and even on car tires and clothing. The Colorado Noxious Weed Act outlines duties and laws regarding noxious weeds in Colorado. The act states, “It is the duty of ALL persons to use integrated methods to manage noxious weeds if the same are likely to be materially damaging to the land of neighboring landowners.” Be a responsible citizen by learning to identify and control noxious weeds before they spread and become your neighbor’s problem too.

Noxious Weed Classifications

Noxious weeds in Colorado are categorized into one of three “lists” according to their statewide distribution and need for management.

  • List A species are rare and are subject to eradication wherever detected statewide.
  • List B species have discrete statewide distributions that are subject to eradication, containment, or suppression in portions of the state designated by the state ag commissioner.
  • List C species are widespread and well-established noxious weeds for which control is recommended but not required by the state, although local governing bodies may require management.

A Few Notes About Noxious Weeds

  • An ounce of prevention is worth a pound of cure. It is easier to prevent noxious weeds than to get rid of them. By establishing desired vegetation (grasses and flowers) early on, you reduce the risk of noxious weeds creating strongholds down the road. See the 9 Keys to Successful Seeding for more information on planting desired species.
  • Noxious weed management is an ongoing process. It is not something you do once and are done. You will need to continually monitor and mitigate for noxious weeds throughout your years of land ownership. This is especially important if you do any type of soil-disturbing work or if you bring new soil onto your property. Some noxious weed seeds can remain dormant in soil for many years before springing to life. Thus, you will need to remain vigilant for years to come. PERSISTENCE, PATIENCE, AND PERSEVERANCE MAKE AN UNBEATABLE COMBINATION!
  • Integrated Weed Management is a holistic approach to weed management that integrates different methods of weed control. It incorporates Preventative measures with Chemical, Biological, Mechanical, and Cultural means of control. See the Noxious Weed Guides described below for more details.

Grand and Summit County Noxious Weed Guides

To help landowners learn about noxious weeds and what to do about them, the Middle Park Conservation District and our local Noxious Weed Departments created Noxious Weed Guides for both Grand and Summit Counties. These guides have photos and descriptions for each of the noxious weed species present in that county, suggestions for noxious weed control, and tips for the establishment of good vegetation.

You can access both guides at the following link or by contacting your local Noxious Weed Department. These guides include PHOTOS of our local noxious weeds!!

Each county’s Weed Department also has its own herbicide giveaway program to help landowners in curbing noxious weed encroachment. See their contact info below.

State Noxious Weed Website:

Weed management projects on AGRICULTURAL LANDS have the potential to be funded through CPW’s Habitat Partnership Program (HPP). Contact Middle Park HPP (CPW)  |  970-725-6200 

Organic vs. Inorganic (Chemical) Herbicides

Many people are concerned about the impacts of inorganic (chemical) herbicides on the environment and the potential safety hazards of their applications. As a result, the Summit County Noxious Weed Department researched the topic and performed a field trial to determine the differences in effectiveness between organic and inorganic herbicides. The month-long field trial took place from June 26 to July 26, 2017, in Summit County, Colorado.

Photos of the both test plots prior to herbicide applications showed several live and flourishing noxious weeds (chamomile and thistles). Two days after the appropriate herbicide application, the plants in the Organic Test Plot appeared to be burned (brown and dead). The plants in the Inorganic (Chemical) Test Plot were nodding but were still green in color. One month after the herbicide treatment, the plants in Organic Test Plot had completely recovered and were even flowering. Noxious weeds in the Inorganic (Chemical) Test Plot were totally dead.           

organic vs inorganic herbicide trial

When researching it online, the Summit County Weed Department found that their results were NOT unique. Other studies also revealed that vinegar and salt (the most common ORGANIC mixture) only kills the top growth of the plant (the leaves), but it does nothing to the roots. It is also considered “non-selective,” meaning that it is likely to affect any plant it touches (even desired native species). Repeated applications of ORGANIC HERBICIDE could also change the pH of the soil, eventually making it uninhabitable for most species (good or bad). Treatments must be delayed for one to two days after rain; plants that are waxy or hairy may not absorb the vinegar; and organic herbicides may not be effective after two weeks of germination. Herbicidal Vinegar, vinegar that has stronger concentrations of acetic acid (11% or greater), can cause skin burns, severe eye irritation, and other irreversible bodily harm. Some states even require you to register as a certified Pesticide Applicator prior to using the higher concentration herbicidal vinegar. Lastly, the Summit County Weed Department noted that organic herbicide tends to be corrosive on spraying equipment. Equipment had to be thoroughly cleaned after each use.  

INORGANIC (CHEMICAL) HERCIDES, on the other hand, will kill the whole plant, roots and all. Most, but not all, chemical herbicides are “selective,” meaning they will only kill certain types of plants (not everything). Weather also has minimal impact on chemical herbicides as they are absorbed and translocated rapidly. Once the chemical is absorbed, in most cases, it is also safe for pets, livestock, and wildlife to touch and even eat. Chemical herbicides are not as corrosive and may be left in the sprayer between sprayings. That being said, sprayers should be thoroughly cleaned before switching to a different herbicide and prior to being stored away for the season.

All in all, do your research and make sure you know the facts prior to choosing your herbicide preference. Also, be sure to read the label prior to using any herbicide. the label is the law. Contact Grand County Natural Resources or Summit County Weed Department with questions on herbicides and noxious weeds. Contact info in "Who You Gonna Call" on the right.         

Example Organic Herbicide MixtureExample Inorganic (Chemical) Herbicide Mixture
4 cups household vinegar2 teaspoons Milestone Herbicide
1/4 cup table salt2 teaspoons Induce surfactant
2 teaspoons dish soap3 gallons water

9 Keys to Successful Seeding

It is important to establish competitive & desired vegetation BEFORE weeds establish!!! You can establish good vegetation by planting forbs or seeding with desired grass/wildflower seed mixes of good quality & purity.

Looking to for seeding recommendations or want to buy seed? Contact MPCD

Key #1 – Kill the Weeds First

Ideally, at time of seeding, there should be no actively growing weeds.

Key #2 – Use Adapted Species

Seeding the right species, in the right amount, at the right time is imperative to successful seeding. Selecting species that are adapted for your planting conditions will make all the difference. Soil, climate, elevation, and exposure all factor into species selection.

Key #3 – Prepare a Good Seedbed

A proper seedbed is firm and free of competing vegetation. Correct firmness is when an adult footprint is only slightly visible on the prepared bed prior to the seeding operation. Most species should be planted at a shallow depth of ¼ to ½ inch. Larger seeds can be planted up to 1 inch deep. Seed to soil contact is imperative. If the seedbed is very uneven, consider drainage concerns prior to planting. Where will water pool? If needed, attempt to level out the seeding area by moving soil around or adding soil. Be cautious, though, to verify that any soil you add to the site is weed-free!

Key #4 – Seed at the Right Time

Seeds should be sown when the soil’s moisture and temperature are optimal for seeding. The three main seeding windows in Middle Park are Spring, Late Summer, and Late Fall.

  • Spring (late April-May right after snow melts off)
  • Late Summer (mid July-early August during the summer monsoons)
  • Late Fall (mid to end of October until first perennial snow)

Key #5 – Seed at the Proper Rate

Typically, the seeding rate directly correlates to seed size (larger seed size equals higher seeding rate). However, Mark Volt, the Middle Park District Conservation Technician, says, “On average, you should seed at a rate of 40 seeds per square foot.” If you find it difficult to regulate your seeding rate with small seeds, you can mix in a filler of sand, sawdust, or potting soil to get adequate seed distribution. Keep in mind that drill and broadcast seeders can be calibrated to specific seeding rates, thus minimizing human errors.

Key #6 – Cover Your Seeds

Seeds are lost when wind and water wash them away or birds and small mammals eat them. To increase your seeding success rate, cover your seeds by raking or dragging soil over them. Mulch, in the form of sawdust, straw, or peat moss, also provides good cover. When you look down at your mulched/seeded area, you should see about 50% mulch and 50% soil.

Key #7 – Water, Water, Water

Seeds and seedlings NEED adequate moisture to germinate and grow. Even if you are buying a drought-tolerant seed mix, your little seeds need ample water. Make sure to water lightly and frequently. If you drench them too much, you risk washing them away.

Key #8 – To Fertilize or Not to Fertilize?

To fertilize or not to fertilize, that is the question. The answer is, “IT DEPENDS.” Fertilizer is non-specific, meaning that it will boost the growth of anything that it contacts (including weeds). Because weeds are genetically predisposed to rapid growth and establishment, fertilizer may give them an even bigger boost. The safest option is to wait for ONE growing season to make sure your seeds can outcompete any weeds. Once seed is on the ground, hand pull weeds and avoid herbicide use in the first growing season.

Key #9 – Wait to Graze

If you plan to graze the seeded area, it is best to wait ONE or TWO growing seasons prior to grazing any animals on the site. This will give the sprouts a full year to grow and establish. Otherwise, you may be seeding again before you know it.

Why Did My Grass Not Grow?

A common question we get in our office is Why did the seed I bought not come up?

Though it is easy to automatically assume that the seed must be bad or poor quality, the reality is that so many factors play into the successful germination and survival of grass and wildflower seeds. 

Proper watering; sunlight; soil type, preparation, and compaction; planting depth; herbicide use; seed type and quality; and timing of planting can all play into successful seeding.

There are 4 main requirements for seeds to germinate. If any one of them is missing or compromised, germination may fail.

1) Seed-to-soil contact
2) The right amount of moisture
3) The right temperature
4) Sunlight

Additionally, if the seedbed is the not prepared correctly, is too compact, too soft, or has an unfavorable pH or mineral content, it could also impact your seeding success. 

Seeds that are not adapted to your environment (the proper elevation, moisture and exposure conditions); are planted too deep or too shallow; are subject to too much grazing pressure, foot traffic, erosion, or herbicide use; or are not planted at the proper seeding rate or time of year may also fall flat.

While seed quality and age can impact the success of a seeding, all seed purchased by MPCD is tested by the supplier prior to shipping to determine its germination rate. The mix’s germination rate and packaging date are printed on the seed label. MPCD seeks seed suppliers that package good quality seed with large percentages of pure live seed.

Successful grass seeding is more an art than a chance encounter. While you may have success just tossing some seed on the ground, the likelihood of success is much improved with proper seedbed preparation, proper timing, and proper care. As such, read 9 Keys to Successful Seeding on the previous page.

Final Thought on Seeding

Seeding success often requires a healthy dose of persistence, patience, and perseverance. Some species have seeds that can remain dormant, yet perfectly viable, for years. Others have a naturally low germination rate. Give your seeds time after planting to see if they come up. If they don't sprout within a few months, try again during the next proper seeding window. Maybe the conditions weren't right on the first go but will be right on the second try. 



References: 1, 2, 24, 25, 26


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