Are Herbicides necessary?

Noxious Weeds

Why Use Herbicides? 

As part of an integrated weed management plan

Our mountain landscapes are filled with a rich diversity of trees, shrubs, grasses and flowers. Most are native species, well-adapted to growing harmoniously in their particular spot. Others, however, are relative newcomers to Colorado - native to other countries and continents - and they do not play fair with their Colorado cousins! These interlopers arrive unencumbered by their natural checks and balances from back home, and are super-competitors in their adopted land. The most aggressive and troublesome of these invasive plants are the noxious weeds: by definition, they are seriously detrimental to our health, our livelihoods, and/or our surrounding environment, and we have a legal (and possibly ethical) mandate to stop their spread.

How can we sucessfully manage these noxious weeds so they do not threaten our native plant communities and wildlife, pose a wildfire risk, lower property values or just spoil our enjoyment as mountain landowners? There are several good options in the Integrated Weed Management suite - preventative, mechanical, biological, cultural and/or chemical. Which method (or combination of methods) is most appropriate depends, in part, on what type of plant we are dealing with - annual, biennial or perennial - and how big the infestation is. Let’s look closer.

Mechanical methods of control can work quite well for many annual and biennial plant species (think scentless chamomile and common mullein) - here the most important strategy is to prevent seed production and spread, since these types of plants live for just a year or two, and reproduce only (but prolifically) by seed. Tilling young seedlings, digging or pulling maturing plants, or cutting and bagging the seedheads, will interrupt that seed-focused lifecycle. However, these methods disturb the soil, exposing any previously-buried weed seeds for a new round of germination. So it may take many years of such physical control to rid a property of these weeds if there is an existing seedbank.

What about using mechanical removal for longer-lived noxious weeds? For perennial species (think Canada thistle and leafy spurge), preventing seed formation and dispersal is only part of the solution - noxious weeds in this category also have robust and extensive root systems that persist year after year deep below ground. Pulling or digging up a perennial plant rarely removes the entire root system, and can just stimulate new vigorous shoot production in the root fragments that remain. If removing plants by hand is rarely effective for perennial weeds, nor practical for large expanses of annuals and biennials, what are better options?

Mowing or grazing are cultural methods often used to help manage weeds, and they can be a valuable component of an integrated approach. These practices can knock back the growth of a vigorous stand of weeds and also delay or reduce seed production if done at the right time. However, they will rarely eliminate deep-rooted perennials, and can inadvertently spread weed seed to other locations through equipment or grazing animals. Biological controls - where insects or pathogens specific to a particular noxious weed host species, are introduced to feed on the plant or otherwise disrupt its invasive vigor over the years - can work well on very large acreages of specific weeds, but less so on smaller properties, and will never eliminate a noxious weed population, but just reduce it to a less-competitive status.

So what other management techniques will work well on a mountain property such as yours or mine, that is neither very extensive nor very small, that has native vegetation to protect, and a variety of weed types to eliminate or control? Is there a method that can be integrated with other approaches, custom-designed for a specific weed problem, and still leave desirable plants unharmed? Yes! Chemical control...

Herbicides. These chemicals, when carefully and appropriately applied, can kill off individual noxious weeds without disturbing the surrounding soil or disrupting other vegetation. Herbicides spot-sprayed on weed foliage interfere with one or more metabolic processes in the targeted plant (growth regulation, photosynthesis or amino acid synthesis, for example) without having a significant or negative impact on the surrounding environment. Herbicides can be broad-spectrum or selective, and also contact or systemic in their approach. Let’s look at a few examples in use today.

One herbicide many folks are familiar with is Roundup, an over-the-counter broad-spectrum product that will routinely kill or injure any plant it touches. Once sprayed on plant foliage, this herbicide, being systemic, will also be carried internally ("translocated') down to the roots to impact them too. Industrial-strength vinegar, another broad-spectrum herbicide, has a similar indiscriminate effect. Vinegar is also only a contact herbicide, working merely on the above-ground plant parts, and not able to be carried to the roots. Moreover, its high acidity can have additional negative impacts on soil health if overused.  While these products certainly have their place in eliminating unwanted vegetation on hardscaped areas such as driveways, their heavy-handed approach is of limited value where the problem weeds are growing amongst native or desirable grasses, shrubs and wildflowers that could be impacted. Fireweed Ecological Services rarely uses Roundup, and has better, more nuanced options than concentrated vinegar.

For the nimble work of managing a variety of noxious weeds without harming the native plants around them, it is really helpful to use selective herbicides that are designed to impact only certain plant types(broadleaved plants but not grasses, for example).  If it is a systemic herbicide too, it can also successfully deal with the deep roots of perennial weeds by translocating throughout those individual plants. Fireweed ES finds that systemic selective herbicides such as Milestone, Transline, Plateau and 2,4-D can be very effective (especially in combination) in controlling creeping noxious weeds such as Canada thistle and leafy spurge as well as troublesome annual and biennial weeds.

Pre-emergent herbicides work differently than the above post-emergent or foliar formulations, by preventing weed seeds from germinating. When broadcast-sprayed on the weed-infested ground, pre-emergents can be successful in stopping sprouting of seeds of both short and long-lived weed species. Rejuvra is a pre-emergent that Fireweed ES regularly applies to manage infestations of the winter annual, cheatgrass, on mountain properties, removing a fire-hazard in the process.

Herbicides must always be used according to the (extensive!) label directions that come with the product. By being careful to wear the correct PPE, apply at the specified rates, on only the listed plant species, in recommended environments and under conducive weather conditions (no or low wind, temperatures not too hot or too cold etc), one can avoid hazardous risk to oneself and the surroundings, including wildlife and native plants. FES typically just uses spot-spraying on specific target weed plants unless treating large patches of cheatgrass or other denser weeds where broadcast-spraying (especially for pre-emergent herbicide) is appropriate and necessary. Professional commericial applicators like myself have to pass exams to become certified in herbicide application in various landscape types by the Colorado Department of Agriculture, and carry appropriate insurance before we can work on private lands.

Using a combination of weed control methods as part of an integrated management plan is the most effective approach when dealing with multiple weed species with a diversity of characteristics. Just as in medicine, where we may find adopting a healthier diet or exercising may work for some ailments, but antibiotics or chemotherapy are necessary for more aggressive illnesses, so it is with environmental health: Our ecosystems may sometimes be able to be restored to health by purely mechanical, cultural or biological management practices. If sickened by unbridled “novel” invasive plants, however, they may need a jumpstart with herbicide treatments until the issue is under control and other management methods can be used to help nature heal itself from then on. Our ultimate goal is land that is natural, healthy and resilient enough that by simply using preventative measures to avoid disturbance or disruption, we can ensure that weeds can no longer infiltrate our land and wreak havoc.

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