Forbs, young shrubs and trees
High
Moderate-high ($1000–$5000/gross)
Low/no risk
Low-moderate risk
Low risk
Low/no
Overview
Severing roots, also known as shovel shear and subsurface cutting, is a technique for severing the roots of plants just below (up to a few inches) the root crown and soil surface. It functions by completely separating the portions of the plant that harvest light from the portions that harvest water and nutrients. This starves both portions of the plant from needed materials and the plant dies if the stem cannot produce more roots and the roots cannot produce more stems.
This technique is useful for the control of annual and young perennial weeds that are interspersed in areas with higher native plant cover. It is typically applied in areas where cover of the target species is low and minimizing disturbance to soil and surrounding vegetation is a priority. It can also be used in areas where the soil is fairly hard, making pulling difficult or impractical. Cutting through the soil just below the surface protects the soil structure below. The space required to maneuver the tool is small since the tool travels only the distance required to slice through the roots.
This technique can be useful where precise work is needed to not damage surrounding plants and is generally low impact with regard to cultural resource concerns because of the precision of the work. It is also not vehicle dependent as you can walk to the treatment site carrying the necessary tools. When used alone in ideal conditions on ideal species it is an effective control method. This is, however, highly scale dependent as larger areas and infestations may require more personnel and time. It can also be used as a follow-up control method on seedlings and very young perennials in working toward eradication. If a large-scale treatment of another method has been implemented this is an ideal way to conduct follow-up removal work.
How to Use
This technique works by severing the plant below the root crown to prevent crown sprouting. A sharp, sturdy tool is driven through the ground at an angle where it travels completely through the main root. This is most efficiently implemented with a tool and conditions where this can be done with one strike per plant. It is highly selective and most efficient when done well before the target species sets seed and when the biomass can be left in place. It is an effective control method on annuals and very young perennials (where severing the root still requires little effort).
To implement this technique and sever a taproot, place a sharpened tool at the base of the plant, angling under the stem, and push it as far below ground as possible. To prevent sprouting, the taproot should be severed below the root crown. The tool should enter and exit the soil in a straight line, without a digging motion. If done correctly, the severing motion should not disturb much soil at all. Depending on the species, it may be possible to feel the resistance when the tool passes through the root and know when it has been severed. The plant may fall over on its own immediately after severing, which is also a good indicator.
The tools used for this technique vary by target root size, precision needed, and user comfort. Various tools used are: hori hori, lettuce knife, kitchen knife, steak knife, weeding pick, forked weeder, sharpened flat-ended shovel, trenching shovel, spade shovel, fire shovel, and root slayer shovel, pickaxe and mattock. Sharpness, angle, and end shape are important decision makers when choosing a tool. Notched “v” tips are a very effective end shape.
The angle is important for worker ergonomics. A tool with a shape that can be used without much added motion from normal carrying is preferred (angled more for tools used while standing than for knife-like tools). Sharper tools will cut better but may dull quickly in gravely soils.
As each plant is treated individually this technique is highly selective. Non-target damage is only expected if the non-target species is growing close enough to the target species that its roots could be injured by the severing stroke. This is roughly the width of the tool used so hori horis and knives will have less impact than larger shovels.
This method works best in environments open enough to be easily moved through as it saves time. Many tools can be carried easily or be used as walking sticks when not in use (being cautious of sharp ends). It can be effective any time of year but will be slower if done after seed production when the biomass cannot be left behind.
This method works mainly on plants with tap roots, including many annual and biennial thistles (including Carduus nutans, Cirsium vulgare, Dipsacus species, Onopordum acanthium, young Cynara cardunculus, Gysophila paniculata, Arctium lappa), as well as Pastinaca sativa, mustards, young castor bean, young tamarisk, and many rosette-forming tap-rooted forbs. Note that mature Cynara cardunculus (artichoke thistle) will resprout when roots are cut.
Non-Chemical Weed Control: Severing Roots, Shani Pynn from Cal-IPC on Vimeo.
Special Tips
Make sure tools are sharp and stay that way. Carry a hand file or sharpener in the field to maintain this.
In harder soil conditions or with thicker roots a larger shovel can be set in position and kicked to sever the root. If driving a shovel by boot, shovels with wider footrests are preferred. While slightly heavier, they can reduce foot pain and boot wear from repeated striking. However, in instances where multiple kicks are necessary per plant this technique will rapidly become more tiring and less cost effective.
In wet conditions, modification can be made by holding the plant while cutting and then bagging or tossing it to a drier area. This is because some plants, especially those with thick roots, can re-root into wet soil and continue growing. This is most effective with small numbers of plants.
For larger trees such as tamarisk, a scaled up, more impactful version of this technique involves cutting deep below ground and backfilling the resulting hole up to one foot deep to prevent resprouting. This approach is also mentioned as part of Whole Plant Removal: Hand / Hand Tools.
Optimal Conditions for Use
Severing is especially effective in drier site conditions as wet areas support plants that are more prone to resprouting. It is best done before seed is mature enough to ripen on severed stems so they can be left in place. Optimal conditions would be an infested area with clustered patches or scattered low density target plants interspersed with desirable vegetation. Optimal soils are fine (sandy, silty) and uncompacted types with little to no larger material (cobble, etc.). Flat to moderate (<40%) slopes are preferred as they allow safer movement with sharp tools.
Caveats
Plants growing in very wet conditions have more resprouting potential and are therefore often not successfully controlled with this method. Severed stems may be able to reestablish. Reduce this risk by moving stems away from soil. Likewise, this technique may have a lower efficacy in areas with higher annual rainfall.
Severing underground structures can be difficult in deserts, wetlands, and rocky soils. While this technique works well in dry conditions, it does not do well in dry, hard, clay soil where it is difficult to get a sharp tool through the ground. Soil must be soft enough to allow the cutting tool to be pushed through by hand or boot power and must not be so wet that plants left on the soil surface will be wet enough to root again.
This technique is counterproductive on rhizomatous perennials, perennials with fibrous roots (e.g., perennial grasses), or species that reproduce by underground vegetative structures (bulbs, tubers, nutlets, etc.).
Some species can resprout from taproots (e.g., artichoke thistle). This technique can prevent seed production but will not provide full control. Repeat visits will be necessary.
Large infestations are labor intensive and may be more feasibly controlled with other methods. Under optimal conditions a one- to two-person crew can handle a quarter acre of net infested area in a day. Larger areas and higher densities become demoralizing, time consuming, and may increase the risks of repetitive stress injuries. Severing underground structures also does not outpace populations with a high rate of spread.
Potential Hazards to Humans, Environment, and Cultural Resources
Human safety. Moderate risk. Hazards include cutting risks by workers using sharp hand tools. On steeper slopes it will be safer to use versions of this technique that involve kneeling rather than standing. Repetitive stress injury will be the most likely injury for this method. Wrists, elbows (bursitis), and shoulders may be affected. Because work needs to occur low to the ground, persons may either be kneeling or standing, which leads potentially to stooping and back injury, especially if larger plants are being severed. Longer handled sharp tools require care when working in close proximity groups to avoid striking each other when carrying them during travel (e.g., turning quickly with shovel over shoulder). Maintain a suitable safe distance between workers and ensure they have any Personal Protective Equipment (PPE) associated with the chosen work tools such as gloves and eye protection where necessary. Also ensure workers are trained to use these tools safely in relation to the individual environmental hazards of the work site.
Cultural resources. Low risk. Because severing underground structures does not involve significant soil disturbance it is not likely to disturb cultural resources. Nonetheless, cultural resource experts should be consulted prior to initiating work if a site is located near a cultural resource area of concern.
General environment. Low risk. There is little concern of hazards to non-target species or the environment because of the high specificity and minimal impact of this technique.
Sensitive species. Low risk. This technique penetrates the soil quickly. Care should be taken if there may be hibernating amphibians of concern in the area. However, this technique can be effective at fairly low depth soil penetration. Normal precautions should be followed to avoid nesting species.
Erosion. Low risk. If done properly, this technique minimizes soil disturbance by severing structures below ground and typically leaving them in place.
Consider Combining with the Following Non-Chemical Methods
Severing underground structures may be used as a follow-up treatment for seedlings or saplings after other techniques have been used for initial control of larger tree or shrub species or for high-density removal. Large-scale high-density treatments can become less cost effective toward the tail end of a project when weed populations are too spread out. At that point this technique can be quite useful. As the tools are light to carry it is useful to combine this technique with site visits for other purposes to opportunistically control outlier target plants.
Don’t Use This Technique When/For
This technique is ineffective on established perennials and species with bulblets or corms that readily resprout. In some cases, underground severing can actually promote spread of these plants. It also cannot be used in extremely rocky soils, extremely hard soils, or under very wet conditions.
References
Tu, M., C. Hurd, and J.M. Randall. 2001. Weed Control Methods Handbook: Tools & Techniques for Use in Natural Areas. All U.S. Government Documents (Utah Regional Depository). Paper 533. http://digitalcommons.usu.edu/533
Authors and Credit
Lead Author: Shani Pynn, Senior Plant Restoration Ecologist, Riverside Corona Resource Conservation District
Co-authors:
Pamela Beitz, Integrated Pest
Management Specialist, East Bay Regional Parks District
Jutta Burger, Science Program
Director, California Invasive Plant Council
Dan Lubin, Environmental
Scientist, California State Parks
Tom Reyes, Integrated Pest
Management Coordinator, Midpeninsula Regional Open
Space District
Additional Contributors:
Garrett Dickman, Botanist, National Park Service.
Suggested Citation:
Pynn, S., P. Beitz, J. Burger, D. Lubin, and T. Reyes. Severing Roots. Weed Control User Tool (WeedCUT) – Methods for Managing Weeds in Wildlands. weedcut.ipm.ucanr.edu. California Invasive Plant Council (Cal-IPC) and University of California Statewide Integrated Pest Management Program (UC IPM). Accessed [date].
Efficacies
| Rating | |||
|---|---|---|---|
| Plant | Flowering Period | ||
| Winter | Good | ||
| Spring | Good | ||
| Summer | Good | ||
| Fall | Good | ||
| Multiple Seasons | Fair | ||
| None | Poor | ||
| Plant | Germination | ||
| Winter | Good | ||
| Winter / Spring | Good | ||
| Spring / Summer | Good | ||
| Opportunistic | Good | ||
| Plant | Palatability | ||
| Yes | No Information | ||
| No | No Information | ||
| Partial | No Information | ||
| Plant | Plant Growth Form | ||
| Grass | Poor | ||
| Forb | Good | ||
| Shrub | Good | ||
| Tree | Fair | ||
| Vine | Poor | ||
| Plant | Plant Type | ||
| Annual | Good | ||
| Biennial | Good | ||
| Perennial | Good | ||
| Plant | Propagule Production | ||
| Low (<1000/square meter) | Good | ||
| Moderate (1000–10,000/square meter) | Good | ||
| High (>10,000/square meter) | Fair | ||
| Plant | Rate of Spread | ||
| High (doubling in <10 year) | Fair | ||
| Moderate (50–75% increase in 10 years) | Good | ||
| Slow Rate (25% increase in 10 years) | Good | ||
| Plant | Resprouting / Regenerative Capacity | ||
| Low | Good | ||
| Moderate | Fair | ||
| High | Poor | ||
| None | Excellent | ||
| Plant | Seed Life | ||
| Short (≤3 years) | Good | ||
| Moderate (4–10 years) | Good | ||
| Long (>10 years) | Fair | ||
| Plant | Type of Reproduction | ||
| Seed | Good | ||
| Vegetative | Poor | ||
| Seed & Vegetative | Poor | ||
| Plant | Type of Vegetative Reproduction | ||
| Rhizome / Stolon / Stem | Ineffective | ||
| Bulb / Corm / Tuber | Poor | ||
| Root sprout / Sucker / Crown sprout | Fair | ||
| Site | Existing Desirable Plant Cover | ||
| <10% | Good | ||
| 10–25% | Good | ||
| 26–50% | Good | ||
| 51–75% | Good | ||
| >75% | Good | ||
| Site | Ground Condition | ||
| Muddy | Poor | ||
| Smooth | Good | ||
| Cobbly | Fair | ||
| Rocky | Poor | ||
| Site | Habitat | ||
| Marsh / Wetland | Poor | ||
| Riparian | Poor | ||
| Grassland | Good | ||
| Shrubland | Good | ||
| Woodland / Forest | Good | ||
| Site | Level of Tolerable Disturbance | ||
| Low | Good | ||
| Medium | Good | ||
| High | Good | ||
| Site | Slope | ||
| Flat | Good | ||
| Moderate (10–40%) | Good | ||
| Steep (>40%) | Fair | ||
| Site | Target Area | ||
| <40 square feet | Good | ||
| 0.001–0.01 acre | Good | ||
| 0.02–0.1 acre | Fair | ||
| 0.2–1 acre | Fair | ||
| 2–10 acres | Poor | ||
| 11–50 acres | Ineffective | ||
| 51–100 acres | Ineffective | ||
| >100 acres | Ineffective | ||
| Site | Targeted Invasive Plant Cover | ||
| <1% | Good | ||
| 1–10% | Good | ||
| 11–25% | Good | ||
| 26–50% | Fair | ||
| 51–75% | Poor | ||
| >75% | Poor | ||
| Site | Vehicle Accessibility | ||
| Roadside | Good | ||
| <100 feet from road | Good | ||
| 100–1000 feet from road | Good | ||
| >1000 feet from road | Fair | ||
