Russian knapweed was formerly known as Acroptilon repens L., but now goes by the scientific name of Rhaponticum repens L. It belongs to the Sunflower family.
This invasive plant is a noxious weed in many states in the USA. In this guide, we will tackle its threat to the ecosystem and what you can do to deal with it effectively.
What is Russian Knapweed?
This weed goes by a lot of names, but they all point to the same noxious plant. Some of the names include creeping knapweed, Turestan thistle, hardhead, mountain bluet, and Russian cornflower.
This perennial, which is not native to North America, creeps, thus its reference as creeping knapweed. Of all knapweed species known in the USA, studies show that this is the most common as it has spread over a wide area.
It is quite common to come across this weed in the northern states, with Montana being an excellent example of the same. Over time, it has spread to other states where its presence is causing headaches to many people.
You can tell its difference from other knapweed species by looking at its rhizomes. They have a scaly dark brown to black hue. Additionally, its flowering bract is not like that of other varieties.
Origin and distribution
This weed is native to Eurasia, and it made its way to the USA through contaminated Turkestan alfalfa. That was in the early 1900s, after which it spread to the central and western regions in the United States. Given that this weed is hard to control, it took a short period before it invaded a large number of states.
To make things worse, people once used it as a means of controlling soil erosion, thereby encouraging its spread across farmland and cropland.
Most affected areas by Russian knapweed in the US
How to identify Russian Knapweed
The good thing is that this weed takes time to establish. The bad thing is that once it takes root, dealing with it becomes a problem. Plus, it lives long and creeps to distant places.
Given this nature, it is best to deal with it early, and all this starts with identifying the weed. How can you know that you have knapweed in your outdoors? Here is what you should be on the lookout for:
Its rosette, which comes out towards the start of spring, has a grayish-green hue with some hairs on its base. Flowering starts anytime from June and continues through September. Color of the flowers varies, but you will find that it lies anywhere from pink to lavender.
The flowers resemble thistles and feature heads in the ranges of a quarter to half an inch. The tips of the rounded bracts appear papery.
If all this looks similar to a plant in your outdoors, you may have a cause for worry. From the flowers, move on to the stem. Knapweed will have a stem measuring eighteen to thirty-six feet in height. That will depend on its age as well as how favorable the conditions are. Along this stem, you will find hairs that feel and look like cobwebs.
The stem leads to a vertical root system. The thing with the root is that it can grow to depths of up to twenty feet. This stem is scaly with a brownish-black hue and long-living.
If all these characteristics are similar to a plant in your home, you had better act fast before it leads to the establishment of more weeds.
Growth characteristics
Surrounding the scales are root buds through which rhizomes emerge, creating a dense population of plants. Other than propagation through rhizomes, the knapweed also depends on seed production.
A single plant can produce as many as fifty to five hundred seeds, depending on the conditions. These seeds fall off the parent plant or get dispersed and can remain viable for up to three years.
As the knapweed grows, it releases allelopathic chemicals into the environment. These chemicals work in inhibiting the growth of other plants. The weed is thus able to avoid competition for nutrients, and it can establish at a fast rate.
Additionally, it contains sesquiterpene lactones, which are toxic to horses. Thus, having this weed in an area where horses graze could lead to the death of the animals through ingestion.
You should note that this weed is relatively shade-intolerant. As such, where it grows in shaded regions, it exhibits slower growth as compared to growth in sunny areas.
Threats: Why is Russian Knapweed a noxious weed?
This weed creates monocultures and grows in dense stands once established. As it does so, it exudes allelopathies to the surrounding environment, which slows down the growth of other plants. As a result, other plants get phased out, including natives and desirable plants.
Where this weed establishes in farmland, a farmer is likely to face reductions in crop yield, which would affect the economic wellbeing of the affected person. An excellent example of this invasion would be in Nevada. Studies show that at least 75,000 acres had Russian Knapweed by the start of the twenty-first century.
As knapweed matures, it releases seeds into the environment. These seeds are small and are hard to tell apart from other seeds of this size. Thus, contaminating crop seed and hay with knapweed seeds is easy.
In this way, it reduces the value of hay, which is a loss to the farmer. Also, where it gets consumed by horse, the animals could die owing to its toxicity. The horses develop what is known as the chewing disease, which keeps them from chewing food. The symptoms take over quickly, and given the lack of effective treatments for this, the animal dies.
Furthermore, this weed has the upper hand when it comes to vegetative production. You see, most plants emerge towards spring, while others may take longer. But with knapweed, emergence takes place way earlier than this.
In this way, it can take up nutrients and water and have a head-start on the other species. By the time the natives and desirables emerge, they have already lost the race. That means that pasturelands have less desirable foliage for animals, increasing the risk of horses feeding on this weed.
Another bad thing about this weed is that it can adapt to different soil types. And yes, that includes alkaline and poorly-drained soils. However, it does have a preference for moist yet well-draining soils.
In this light, it will spread over pasturelands, alfalfa fields, croplands, roadsides, riparian areas, rangelands, irrigated fields, and river bottoms, among other places.
How does Russian Knapweed spread?
This weed can spread in two ways: root fragments and seeds. However, root fragments are the most common means of propagation as this plant has an extensive and creeping root system. Where the root fragment measures an inch or more in length, it can give rise to another plant.
However, it needs to be at a depth of six inches or less. Any more than six inches and its chances of survival significantly reduce.
Seeds are also another way of propagation as they fall off the plant when they mature. Both seeds and root fragments find their way into other areas through dispersal. In some cases, it is by the water where the plant grows in wet conditions such as an irrigated area.
In other instances, the dispersal is by human beings during harvesting and transportation processes. For example, the fragments or seeds would be in the hay.
And in other scenarios, the fragments and seeds could find their way to another area by attaching to undercarriages of vehicles. The same goes for equipment used in infested areas.
As the plants grow, they alter the conditions in the soil to make them more favorable to their growth. An example would be the increase in zinc concentration in the upper soil layers. As such, dealing with this weed requires that you deal with the soil conditions as well.
You can try dealing with the plant and find that you are unable to get far in the process owing to the prevailing factors. Let us take a look at how best you can deal with this weed:
Manage the growth of Russian Knapweed
Given the havoc that this weed can wreak on the environment, it is best to prevent its growth rather than to fight it once established. You can do this by having preventative measures in place, monitoring early sightings, and using control methods.
Where the establishment is relatively new, it is best to remove as much of the plants as you can. In such a situation, you can rely on mechanical methods such as hand-pulling.
Where the plants have taken root, it is best to combine the various control methods in eradicating the plants. That is to say; you would use cultural, chemical, and physical means to get to the root of the problem. As you do so, you should ensure you treat the edge of the infestation to keep the weed from spreading to other areas.
The good thing with perennial creeping weeds is that you can attack them through depleting their food reserves. Target the nutrients in the root systems, and your work will be halfway done. Here is how you can manage the growth of this weed:
Prevention
As the adage goes, prevention is better than cure. And it could not be more accurate than in this case. The energy taken to eradicate Russian knapweed is much more than that spent in prevention. Some of the measures you can take include:
Encourage Healthy Plants
The more desirable plants thrive, the harder it will be for the knapweed to invade an area. That means you should have a ground cover on the farmland and reseed dry patches after disturbance.
You can use grasses as they spread fast and take root with ease. Also, work on your grazing practices such that you rotate the animals. Overgrazing leaves the ground bare, and it creates an avenue for knapweed to invade the land.
Monitoring
Use the characteristics outlined in the identification to look out for any infestations. Where you come across the weed, put this down in a book, mapping the area where you found it.
If there have been other infestations in the past, also put this down. Report the sighting to the relevant authority to ensure people are aware of the infestation as you choose a suitable eradication method.
Do not let the new weeds stay for long before using a control measure as they will spread over your land in no time.
Integration
When dealing with the weeds, it is best to use a combination of the control methods. While this concept may not appeal to organic farmers, it helps to note that integrated control provides the best and fastest results. Thus, embrace all means of control, where you can.
Finally, be cautious when buying seed and hay and always opt for certified weed-free products. In this way, you will not run the risk of introducing this weed to your farm.
Control methods of Russian Knapweed
What happens when you have a Russian knapweed infestation on your farm? What can you do? Well, the choice of control method will depend on a lot of factors.
You need to consider how you use the land, the conditions of the land, how intense the infestation is as well as the presence of other plants. Additionally, you need to think about the cost of the treatment and how fast the results will be visible.
If you want fast and effective results, it is best to combine all the methods. Let us break down each control measure:
Physical control
There are tons of physical means you could use to deal with this weed. However, studies show that physical methods are often not enough when used devoid of other means. It is thus best to combine these efforts with chemical applications for long-lasting results.
1. Hand Pulling
Where the level of infestation is small, you can rely on pulling out the weeds by their roots. Alternatively, you could use a hoe in this process, ensuring that you get all the fragments and leave none in the ground. This process has shown results when repeated yearly over some time.
It is easier to dig up the weeds towards the end of spring as the soil is moist during this period. Additionally, the weeds are yet to finish bolting.
When digging up the plants, ensure that you do not leave root fragments in the ground as they would encourage new growths. Also, dress appropriately for safety purposes. The debris should get disposed of in a manner in which it cannot get to other areas.
While some people prefer burning the fragments, you could also bag them and put them in a landfill. Leaving the fragments in a pile to dry only encourages the spread of the knapweed.
2. Tilling
Cultivating the land has also been shown to eradicate these weeds. However, doing so without chemical application only works to enhance the growth of the weeds. When you cut the roots, the fragments spread further, and without any chemicals in play, they sprout.
3. Cutting
You can also opt to periodically cut the weeds as this will discourage the growth of new shoots. Note that this only works in preventing further spread of the weed. It cannot work in eradication unless used in combination with chemical applications.
4. Should you burn knapweed?
It all depends. If you are burning debris from hand pulling or cutting practices, this is a good idea. However, if you choose to burn a knapweed population in the hope of eradicating it, this will not work.
The plants will recover fast and will even be stronger than they were before. Getting rid of them will, therefore, be more laborious.
Cultural control
This control measure is all about preventing the spread of this weed, monitoring it, and dealing with it in the early stages. How does this work?
1. Dissemination of information
When people know what to look for and the dangers of this species, they will be more alert to their surroundings. In this way, the general public can be on the lookout and can report any new findings. Dealing with the weeds can thus take place fast, preventing further spread.
2. Avoidance of infested areas
Unless one has to enter an infested area, people should avoid these areas in totality. In this way, humans, animals, machinery, and cars cannot transport fragments or seeds to other areas.
If people have to pass through such a space, a check should take place to get rid of any seeds or fragments on their persons. The same goes for animals, machinery, and cars.
3. Monitoring
Seeds and root fragments can spread quickly through irrigated water, and there should be measures in place to prevent this. One way would be by screening irrigation water before it moves through the land.
4. Reseeding
Disturbed lands provide an ideal space for the growth of knapweed, and they should thus be under supervision. The best way to deal with this would be to reseed these areas with native perennial grasses. As you do so, till the soil to ensure that the conditions are suitable for the growth of other species.
Biological control
These methods are quite easy, and when used in combination with other means, they work great.
Grazing Regulation
The good thing is that most animals will avoid Russian knapweed as it has a bitter taste. However, they cannot avoid it in infested areas as it will mix with the grass, more so in the early stages.
When cattle, sheep, and goats, take in this weed, they do not suffer adverse effects. However, the same does not hold for horses, which could die after ingesting the weed.
Where there is an infestation, it is best to limit the grazing period to winter, early fall, or the end of summer. As animals graze on land, they encourage the growth of native perennial grasses, and this provides some competition to knapweed.
As spring starts, limit the grazing to give the grasses adequate time to grow and for the seeds to mature.
Biological agents are another way to deal with this weed. However, most of them are still in the testing stage. Those in circulation, such as the gall-forming nematode, have proven to be effective in weakening knapweed.
They attack the stems, root crowns, and leaves, and they quickly spread over large areas. However, they cannot reduce knapweed populations.
Chemical control
If you want this weed out of your outdoors, the best way to go about it would be chemical control. The choice of the chemical will depend on several factors, though. Some chemicals work on leaves and stems while some attack the weed from the roots.
The effectiveness of the chemicals will vary from one land to the other. As such, you need to take weather conditions and the age of the weeds into account.
Though you can eradicate the weeds with one application, it is best to do a follow-up treatment to deal with new growths.
Spraying in fall after a frost has been shown to have better results than at other times. However, this will depend on the manufacturer’s guidelines.
Points to Consider
Note that using chemicals near water sources is not recommended. If you have to do so, ensure that you get a herbicide that works for these conditions.
Also, where you have desirable plants in the area, you should get a chemical that will not affect them. Where this is not possible, you can use the chemical in a way the drift will not get to the plants.
All manufacturers state the requirements as well as the restrictions of their chemicals on their labels. Going through this should give you a clear guideline as to how you should use the herbicide.
Following these rules ensures both your safety and that of your crops. Where you fail to adhere to the stipulations, the weeds could develop resistance, making it harder to get rid of them.
Conclusion
Dealing with Russian Knapweed requires a lot of planning, monitoring, and integrating various control methods.
References
- Russian Knapweed – https://extension.colostate.edu/docs/pubs/natres/03111.pdf
- Field Guide for Managing Russian Knapweed in the Southwest – https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5410125.pdf
- RUSSIAN KNAPWEED (Acroptilon repens) – http://www.library.nd.gov/statedocs/AgDept/Russianknapweed20070905.pdf
