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Eagle County Healthy Landscapes: Stubborn as a weed

Doug Riggins
Special to the Daily
Russian knapweed is found throughout Eagle County and is allelopathic, meaning it exudes a toxic substance in the soil that prevents competing plants from being able to grow. It is only toxic to horses and causes the muscles in their lips, jaws, and tongue to become permanently frozen so they cannot chew.
Special to the Daily

“I’ve been pulling these weeds for years, and each year they seem to come back stronger!” 

If I’ve heard this once, I’ve heard it a thousand times. And if this sounds like you, you’re certainly not alone. Agricultural producers, homeowners, and noxious weed managers have been battling weeds for many, many years.  These pesky plants can range from being a mere nuisance to having major detrimental economical and ecological consequences.

Field bindweed, or perennial morning glory as it is sometimes referred to, is widely considered to be one of the most difficult weeds to control. Once established, it is nearly impossible to eradicate completely. 

On the surface, it doesn’t seem like much compared to the towering thistle plants that we are all familiar with, so why is it so difficult to control? Field bindweed is a low growing, climbing, viney plant decorated with pretty white or pink-ish flowers and arrowhead shaped leaves. 

Like an iceberg, what you see on the surface accounts for only a small percent of the plant’s total biomass. Above ground is a dense, tangled cover that can spread up to 12 feet per year, while underground the roots and rhizomes can extend up to 20 feet laterally and reach depths of 30+ feet! 

The total underground biomass for bindweed has been measured up to five tons per acre. Yikes! It is this massive underground root system that is responsible for many frustrations. These root structures store an enormous amount of carbohydrates that the plant uses for energy to send up new top growth from buds along roots any time top growth is removed, thwarting even the most extensive weed pulling efforts.

Field bindweed is also a major problem for agricultural producers. It can crawl over desirable crops, shading them out, which can reduce crop yields up to 60 percent in addition to clogging equipment used for harvesting crops.

Another difficult weed that is no stranger to Eagle County is Russian knapweed. Thanks to a process called allelopathy, it invades and spreads quickly.  In short, the roots of knapweed excrete their own natural herbicide into the soil to which only they are immune.

By this process, knapweed is able to eliminate competition from surrounding plants and suppresses the germination of any new vegetation.  Much like field bindweed, it too reproduces from underground buds along its roots which can extend well beyond the observable infestation. Because knapweed tends to like moist soils and irrigation ditches, seeds often hitch a ride in the moving water. In addition to devaluing rangeland, Russian knapweed is also toxic horses!

If these problems sound familiar, fear not. This does not have to be the outcome of your weed control efforts. You can be victorious by implementing a persistent combination of control methods.  Patience is key. 

Weeds can be stubborn and you need to be just as stubborn. It’s easy to get frustrated and think what you are doing must be incorrect if the weeds continue to come back year after year. But you could be on the right track, you just need to stay the course. 

Remember that weeds which are difficult to control have a lot of stored food underground which allows them to recover from stress from a variety of any single control method, such as pulling or tilling. This is why a combination of approaches, repeated annually, is essential. 

Timing is also of the utmost importance. Herbicide application is recommended in the fall, so it can hitch a ride on the carbohydrates being translocated down into the roots. Mowing is recommended in the spring, and repeated regularly to prevent flowering and exhaust carbohydrate reserves stored in the roots.

No matter which methods of control you choose, the aim of a successful control program will be to continuously stress the plants to deplete food reserves in their roots and prevent seed production.  

Eagle County Healthy Landscapes is a collaboration between Eagle County Vegetation Management, Open Space, and CSU Extension Office to help inform residents of best management practices for healthy landscapes and to provide resources for weed mitigation, collaborative land management, and local flora. Visit http://www.eaglecounty.us/weeds/ for guides, event details and other resources.


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