With the recent increase in the popularity of skid steer attachments for brush removal, OSU has also seen an increase in the prevalence of questions related to chemically controlling re-sprouts that occur after the removal operation. While these pieces of equipment make the job easier, unfortunately, if used alone they also reduce the effectiveness of foliar herbicide applications on re-sprouting brush species in the near future.
While species such as Eastern redcedar can be fully controlled by cutting them below their green limbs, some species of trees will regrow from buds present on the crown or root. Examples of crown budding species are oak, hickory, elm and Osage orange, while commonly encountered root budding species are honey locust and persimmon. This indicates that while clipping these trees will temporarily remove them from the landscape, they will also re-sprout from existing rootstock and return in the very near future.
The shoots mirror the roots
In general agronomy terms, the shoots (aboveground plant portion) of an unmolested plant typically have similar mass to the roots. This basic of plant physiology allows for efficient uptake of foliar applied herbicides and subsequent translocation to the root system, achieving desired long-term control.
However, if we remove the top growth of a re-sprouting species, the ratio of leaf surface area in relation to root mass has been reduced drastically and sufficient root kill through a foliar application of herbicide is likely impossible. In addition, there is a disproportionately large root system now supplying the small “sprout” with all the elements needed for fast regrowth in the short term ( See Figure 1 below).
Over the next few years, although the re-sprout continues to grow extremely fast, the photosynthesis occurring in the leaves is insufficient to supply the energy needed by the large root mass and therefore a portion of the root system dies back to a sustainable level for the plant. It is at this point when foliar herbicide applications become an option on the table once more.
For this reason, dealing with root or crown sprouting species necessitates these options in decreasing order of preference (combination of control level, time and economics):
1. Apply chemical to the freshly cut stump of re-sprouting tree species.
a. Usually mixed with fuel oil, apply within 30 minutes of cutting.
2. Use an approved product/method to control trees prior to mechanical removal.
a. This could include foliar sprays or basal treatments.
3. Apply a post-harvest soil active herbicide labeled for the offending species.
a. Relies on root uptake and therefore rainfall, not reliable on clay soils.
4. Allow at least 3-4 years of regrowth before using a foliar spray application.
a. Allows time for increased leaf area and decreased root mass.
5. Spray a broadcast treatment option for 2-3 years in a row on re-sprouts.
a. While effective, this method is costly.
So, if you’re contemplating using a skid steer for mechanical tree removal, they are a great option. However, remember to consider the growth habit of the tree species at hand before firing up. Identify what species are present and if they are notorious for re-sprouting. Determine the proper and least cost herbicide treatment for consistent root control. Some tree saw/shear options come with an onboard herbicide reservoir and pump, allowing you to treat the cut stump from the cab. (Source: Brian Pugh, OSU Extension Area Agronomist; June 2018 Timely Topics)
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