Answer: Thank you for your recent request for information from ATTRA, the National Sustainable Agriculture Information Service. I am pleased to provide you with information on controlling thorny locust.
Brush Control Practices
Mature, single-stemmed trees provide shade for livestock and can increase the aesthetics of a landscape if they are not too numerous. They are also much more difficult to remove. For this reason it is advisable to concentrate on new seedlings and young bushes and trees. If the infestation is small, use a grubber or root plow to remove these plants individually. If the infestation is wide-spread, encompassing small and medium-size trees and bushes, consider root plowing, chaining, or roller chopping followed by a controlled burn to remove most of the biomass. It will most likely be necessary to grub out re-sprouts for several years after to obtain optimal control.
Mechanical methods of brush control have varying levels of success. Methods such as chaining or mowing, are more expensive than other practices such as grazing and herbicide use because of high inputs for energy, labor, and equipment. For some species, like locust, even chemical control may not be completely successful without repeated applications and constant attention to new growth. Having brush on your land can be exasperating, but if kept in check can actually become a beneficial contribution to a farm, such as providing cover and food for wildlife and serving as riparian buffers.
Mowing is discouraged as a control method for many brush species, because this activity trains the tree to become a bush. Repeated mowings often encourage crown development, and in general make future control more difficult. Some species, like eastern red cedar, however, can be controlled by cutting them below the first branch, as they will not regrow after cut in this manner.
Grubbing is effective if you are able to remove the basal bud zone. This is an enlarged portion of the root just below the soil line on species like juniper, mesquite, and locust. It is the principle carbohydrate storage structure and the source of future sproutings. Basal bud removal remains the best way to effectively reduce re-sprouting of most brush species.
Grubbing can be accomplished manually for small infestations with the use of a hand grubbing hoe to remove single seedlings and small plants. For larger infestations, a mechanical root plow attached to a tractor is more appropriate.
If you are able, you can conduct a burn after you have grubbed up the stumps and basal bud crowns. Grubbing exposes sensitive plant tissue and builds up fuel necessary for an intensely hot burn. If the fire is not hot enough, it will not kill the plant but merely defoliate it and encourage it to re-sprout. Make sure you contact your local USDA-NRCS office or county Extension agent if you plan on conducting a burn. They will be able to advise you on the legality of this activity, and may be able to offer practical assistance.
Chemical Brush Control: Organic Alternatives
Synthetic herbicides for brush control are usually systemic herbicides that translocate throughout the plant and kill living tissue by disrupting life processes. Organic herbicides do not have the same mode of action, nor the efficacy, of synthetic herbicides. Organic and natural herbicides usually consist of plant oils, vinegar, soap solutions. The oils and acids in natural herbicides work to desiccate the leaves, and the soap acts as a sticking agent. Natural herbicides are only a "burn down" chemical, and will not kill the whole plant. Repeated treatments will be necessary to use up the energy reserves in the roots as they resprout. Organic and natural herbicides work best on annual plants, including grasses and forbs, especially while in the succulent vegetative stage. They are less effective on perennial plants and even less effective on woody species. For continued long-term control, I recommend using a multi-faceted approach to include grazing and mechanical removal.
Grazing is a cultural control method you can use. Pigs or goats will effectively suppress seedlings, and will repeatedly defoliate older shrubs, thereby using up all the plants energy reserves as they try to regrow. Several seasons of grazing has proven effective on many tree and shrub species, including locust, mesquite, wild rose, and Chinese tallow.
Grazing Pigs for Weed Control
Pigs are very destructive to sod, and this can be of use in pastures with high concentrations of weeds or brush. Pigs root up plants and turn over the soil, all the while manuring it while they graze. It is only necessary to provide shelter, water, and temporary fence such as electric netting to confine them to the area while they graze. The ATTRA publication Hooped Shelters for Hogs (http://attra.ncat.org/attra-pub/hooped.html) discusses the use of easy-to-build hooped structures for hogs. Pigs can be thought of as a pasture renovation tool… and after they leave the pasture, grasses and clovers can be overseeded and harrowed. In addition, the pigs can be marketed locally for added income.
General Stocking Rate Recommendation
According to University of Missouri animal scientists, stocking rates will depend upon soil fertility, quality of pasture, and time of year. Recommended pasture stocking rates are:
Sows with litters 6-8 per acre
Pigs from weaning to 100 pounds 15-30 per acre
Pigs from 100 pounds to market 10-20 per acre
Gestating sows 8-12 per acre
These recommendations assume the use of good quality legume pasture under conditions of adequate moisture. Stocking rates in your area (where soil moisture and precipitation may be more limited than Missouri) should be more conservative at the outset, unless you have a good source of irrigation or good sub-irrigated meadows. These stocking rates can be adjusted up and the pigs can be intensively grazed in areas where weeds need to be controlled. For more info see Joel Salatin’s Experience with Pastured Pigs below.
Source: Wheaton, Howell, and John Rea. No date. Forages for swine. University of Missouri Extension.
Joel Salatin’s Experience with Pastured Pigs (in Virginia)
Joel’s pastures are two acres in size, and he uses electric fence to subdivide them into eight, 1/4 acre paddocks. The two acres are stocked with 30 to 50 feeder pigs with a one-ton, self-feeder. The two acre pastures are rested for 12 weeks between each group of feeder pigs grazed. Joel uses crabgrass as the major forage, which has the ability to produce 4 to 6 tons per acre during the growing season in Virginia. Likewise, you would need to use a forage with similar yield potential and grazing resilience in your area to approach the stocking rates and productivity that Joel realizes in Virginia.
Sources: Crabgrass a favorite of pastured pigs, by Allan Nation, and Warm-Season Grass Production Responses to Site and Defoliation Frequency.
Concerns for grazing land degradation
Pigs have a natural rooting behavior that can quickly degrade the pasture if not managed. In some instances this behavior can be good, for instance in situations where a farmer wants to clear a parcel of land from noxious weeds or brush. For grass pastures, especially in semi-arid regions where regrowth is generally slower, increased management to prevent pasture destruction is warranted. A pig tractor is one method for controlling how much land is destroyed through pig behavior. I recommend the following articles which address integrating pig tractors into pasture in detail.
Raising Organic Hogs by the Tractor Method, by Alice Percy
Animal Tractor Systems, by Andy Lee
Resources for more information on pastured swine production
Anon. no date. What is pasture based swine management?
Pasture-Based Swine Management (PBSM) is an alternative approach for raising swine outdoors using pasture as a major source of nutrients, particularly for gestating sows. Compared with confinement or indoor systems for raising hogs, the PBSM approach can offer the producer lower initial costs, lower production costs, and a sustainable method for producing pork. Typical designs of pasture-based systems use low-cost portable housing and electric fencing. Because these systems require no expensive buildings and waste handling equipment, farmers can feasibly down-size or expand their operation depending on prevailing market conditions. In addition, the portability of pasture systems should allow farmers to utilize rented land. These systems should be especially appealing to limited-resource and/or beginning farmers.
Wheaton, Howell, and John Rea. No date. Forages for swine. University of Missouri Extension.
Use of good pasture containing alfalfa, ladino clover, and grass can lower sow feed costs, help maintain high level reproductive capacity of boars, and in many cases increase litter size as compared to confinement raising of hogs.
Karma Glos. 2004. Organic Pork Production. Kingbird Farm
Profitable Pork: Strategies for Hog Producers. Hog Production Systems, Raising Pigs on Pasture http://www.sare.org/publications/hogs/prod_sys04.htm
The Basics of Raising Pigs, by Diane Schivera. Maine Organic Farmers and Gardeners Association. http://www.mofga.org/Default.aspx?tabid=805
Brush Control with Goats
Fire and low density wildlife grazing historically maintained grasslands. However, now brush has encroached and is very difficult and expensive to remove. Goats can be a good tool to help maintain grasslands if you have the necessary fencing and time to manage them.
For best results, match goat grazing to the brush stage of growth, presence of secondary chemicals, and nutrient density. For instance, in winter woody plants have high palatability and low toxicity from secondary chemicals. In addition, protein supplementation increases browsing by goats. For best results use high density grazing for short periods of time to target brush grazing and allow ample time for grass regrowth.
A good resource for using goats as brush control agents can be found in the Targeted Grazing Handbook available online at http://www.cnr.uidaho.edu/rx-grazing/Handbook.htm.
Copper as an alternative?
Some practitioners have suggested the use of copper nails driven into trunks to kill trees. For this to be effective, the copper nail must be able to oxidize and absorb into plant tissue. This chemical reaction takes time and might not release enough copper to cause death. Copper sulfate in appropriate concentration is toxic to trees, and is used as a root killer to prevent root build-up in sewer pipes and drain fields. It is questionable, however, how effective copper nails are in causing tree mortality. A tree wound allows entry for pathogens including fungi, bacteria, viruses, and insects. I am not aware of a method to determine if indeed a tree died of copper toxicity, a disease, or some other condition.
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