A selective treatment affects individual stems and a broadcast treatment affects all stems in an area. If an interfering species is mixed with a high percentage of the desired species, a selective treatment may be used to reduce injury to the desired species.
Editor’s Note: This is the final part of a two-part series on integrated vegetation management. This month’s column will cover the topic of the treatment attribute of broadcast manual and broadcast chemical mode. Check with your state’s cooperative extension or regulatory agency about legal herbicide use.
Mode is selected depending on the desired specificity of the treatment to individual or groups of stems. A selective treatment affects individual stems and a broadcast treatment affects all stems in an area. If an interfering species is mixed with a high percentage of a desired species, a selective treatment may be used to reduce injury to the desired species. Selectivity is possible through physically isolating one stem from others, by using a treatment that only affects a certain species or by applying a treatment at a time of year when desirable species are not susceptible. If the interfering species predominates, or financial or logistical constraints preclude a selective treatment, then a broadcast treatment would be applied.
Read more: Controlling Undesirable Woody Plants: Part 1
The abundance of undesired stems is a good place to start when considering whether to use a selective or broadcast mode. The principle to consider is the fixed cost to visit each stem in a selective treatment. If there are too many stems per acre, that means (1) the cost per acre will become prohibitive and (2) because there are a fixed number of stems per acre the interfering stems have likely displaced the desirable stems. Therefore, a broadcast treatment would have limited relative collateral damage. Although not widely studied, the threshold between selective and broadcast is about 400 stems per acre. Each owner’s situation is a different, so this threshold should only be used as a guide.
- In woodland settings, there are a few options for broadcast manual treatments. These include rotary brush heads on small tracked machines and management intensive grazing.
- Small tracked machines (e.g., Fecon, Timber Ax) can maneuver in many wooded settings and clear vegetation in the lower strata. Depending on the operator, these machines have the potential to selectively avoid desired stems. As with selective manual, this treatment may stimulate root and stump sprouting.
- Management intensive grazing is a grazing strategy often used in silvopasture systems. It requires a high level of grazier awareness and understanding. Management intensive grazing might be preceded by a rotary mower as described already.
- Broadcast chemical treatments are only used when interfering stems fully and almost exclusively dominate the site, and the foliage is at a height where it is accessible to spray equipment.
- Because broadcast chemical treatments open the entire understory, care must be taken to monitor the species that reoccupy the site to assure other interfering species don’t assume dominance.
- A few isolated desired species can often be protected by clipping them at ground level just before spraying. The lack of foliage protects the clipped stems and most will resprout.
- Broadcast chemical treatments are essentially foliar treatments, but done with equipment that sprays broad areas rather than selective targets. In some situations, this treatment is the most efficient and provides the best control of interfering species. Both backpack and tractor/skidder mounted sprayers are available.
ForestConnect is a joint research and extension program funded by the Cornell University Agricultural Experiment Station (Hatch funds) and Cornell Cooperative Extension (Smith Lever funds) received by Cornell University College of Agriculture and Life Science from the National Institutes for Food and Agriculture (NIFA) U.S. Department of Agriculture. Additional educational resources are available.
Photo: Lerrok /istock