Colorado Grazing Lands Conservation Initiative

Responsible grazing lands managers utilize Integrated Weed Management or “IRM” to manage weeds. IRM is the practice of utilizing combinations of cultural, biological and chemical methods to effectively manage weeds. The emphasis is to prevent or limit ecological impact while incurring the smallest financial and manpower investments and the largest level of weed control.  In all cases, it is crucial to understand a specific weed’s growth pattern and physiology.  After a manager carefully identifies a weed problem, relates it to the native plant community, and reviews the alternatives for management, a combination of cultural, biological, and chemical methods can be effective and economical.  Needless to say most managers are looking for better ways to manage chronic weed infestations. Cultural management techniques involve physical disturbances to a noxious weed’s growth cycle. Such practices might include mowing newly established weeds, prescribed grazing to remove seed heads and prevent spread, or prescribed burning if the weed species is not fire propagated. Hand pulling weeds is a “cultural” practice. Biological management techniques usually refer to exposing weed populations to an insect, animal or other plant that either directly preys on the weed or vigorously competes with the weed for space, nutrients, and water. In situations where specific animals prefer to eat the weeds and leave desirable plants alone, such as goats grazing Leafy Spurge, both cultural and biological methods are in place at the same time. Chemical methods usually involve the application of herbicides onto a weed infestation. In a few instances the application of fertilizer can enhance competition with weeds. The use of “weed & feed” on lawns is this type of chemical control practice. Following herbicide label instructions is crucial to reduce risk of problems and enhance the effectiveness of chemical methods.

Colorado has experienced an extended period of drought conditions that has challenged the integrity of all grazing lands and managers in the state.  The extended stress on native and introduced grassland species has harshly impacted desirable plant communities during a period when the fiscal resources of grazing lands managers are also greatly diminished.  Plant community losses have been documented across Colorado that had never before been documented, especially on such a state-wide scale. These impacts created “open space” between desirable plants that lay barren until moisture events came back to Colorado.  And then those open spaces served as a platform for species to upsurge into prominence, many of them noxious weeds.  It is intuitive to most grasslands managers that the economic resources are far overwhelmed by the need to control weeds on the landscape. If something is not implemented the condition (and productivity) of Colorado grazing lands will diminish with the spread of weed infestations.

Managers always begin by looking at the cost of introducing beneficial insects, using herbicides or conducting “prescribed”

grazing on weeds. In reality, we should begin by assessing the impact on productivity since pre-drought periods and then evaluate the impacts of NOT managing weeds. If you have a 1,000 acre pasture that supports 800 Animal Unit Months, ($15/AUM) it generates $12,000 of value each year (gross – not net). The drought impacts reduced productivity to 240 Animal Unit Months or $3,600 per year – a loss of $8,400 in value.  Weed infestations, left unmanaged, could easily reduce productivity by another 20% each consecutive year resulting in an additional loss of $720. Within five years the grazing value of the site could be $0.00. Under this scenario any investment less than the total loss ($12,000/5 = $2,400) may be something to consider, especially since effective management brings income gradually back up and offsets the investment. No matter what combination of IRM you implement – it’s going to cost.

2,4D 1 pt/ac $10.80/gal $2.70/ac

Curtail 2 qt/ac $41/gal $20/ac

Grazon 2 pt/ac $28/gal $7/ac

Tordon 1 pt/ac $88/gal $11/ac

Banvel 1 pt/ac $79/gal $10/ac

Crossbow 2 qt/ac $51/gal $26/ac

If a manager only had to look at economics, the choices made for herbicides would be easy, but each management tool has different characteristics that have bearing on your pasture operation. For instance, please review the characteristics of the same products mentioned above.

There are always other issues like leaching. Many herbicides can runoff or leach into water that travel to other crops and plants, or worse. Applying herbicides carefully according to the label is a good safeguard.

The last question asked should possibly be your first question to focus on. Integrated Weed Management encourages the use of cultural and biological controls as your first step before chemical controls are utilized.

It is recommended that all citizens planning to use herbicides acquire a Private Applicators License from the Environmental

Protection Agency. The process of studying for and taking this free test provides valuable education on safe and effective herbicide use.

Since different species have a different grazing tolerances, habits, and physiology, it is possible to use these characteristics to manage specific weeds. If forced to concentrate on one patch of pasture, animals will eat and impact weeds such as thistles, leafy spurge, salt cedar, and other weeds. You must be careful that the weed targeted is both non-toxic and of value for the specific grazing species. Goats and sheep seem to be more tolerant to a wider range of weed use, but are not able to use all plants. When using grazing animals to target weeds we must also be very cautious to identify and avoid intense grazing in areas where poisonous plants are present. Often poisonous plants spread into “open ground” created during drought impacts on rangelands.

Many rangelands (pastures) are rougher terrain than cultivated fields. Since the “going” is rougher and often larger, special consideration must be given to the equipment type and investment cost. Range and pasture herbicide application often puts stress on equipment and operators. Risk of “drift” with liquid herbicides places an emphasis on the use of dry formulation herbicides on rangeland. This emphasis includes  using low volume herbicides and if at all possible use cultural and biological techniques rather than driving 20-30’ swaths across your pastures.

Weed managers differentiate weed infestations into two basic categories, “acute” and “chronic”. “Acute” infestations are fairly new weed incursions of small acreage size, huge potential for expansion and a weed species that has noxious potential. The encouraged approach is to eradicate these infestations with extreme malice. “Chronic” infestations are well established and usually include large acreage that has exceeded the economic response potential of a manager. These large weed areas need to be “contained”. If at all possible treat the outer boundaries of the infestation and start “shrinking” the size of the infestations. It is important to identify newly seeded “spot infestations” which start from the seed bank of the large initial infestation.

POST-DROUGHT WEED GUIDELINES