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Extension > Garden > Yard and Garden > Trees and shrubs > A practioner's guide to stem girdling roots of trees > Prevention and treatment of SGRs

Prevention and treatment of SGRs

Gary R. Johnson
University of Minnesota

Richard J. Hauer
Minnesota Department of Agriculture

Copyright © 2002 Regents of the University of Minnesota. All rights reserved.

A survey of practicing tree care professionals (Hauer and Johnson 1997) revealed that 88% of the respondents treated trees with SGRs. The two most common treatments were removal of SGRs and treatments to increase tree vitality (e.g., fertilization, irrigation, aeration). Although the practice of removing offending roots has been recommended in countless publications for decades, there is nothing beyond anecdotal evidence that supports this treatment. The most effective "treatment" is prevention.

Fig. 31 - This J-root could easily be removed prior to planting, which would eliminate its potential for stem conflict.

Preventing SGRs
Prevention begins at planting. Watson et al. (1990) speculated that SGRs formed just before or at the time of transplanting with the species they investigated. This speculation has been confirmed with a larger number of species in field studies at the University of Minnesota (Johnson 1999). Therefore, time spent inspecting for and correcting developing SGR problems at planting time is time well-invested and considerably less than that required for a root collar examination after the tree has been in the landscape for several years.

For bare-rooted nursery stock, closely examine the root system and remove encircling roots or 'J' roots that could eventually compress stem tissues (Figure 31). Consider rejecting trees with moderately to severely deformed root systems. For containerized trees, inspect the root systems for encircling woody roots and depth to the root collar flare. If woody roots are encircled, straighten or prune them prior to planting (Figures 32 and 33). If the root collar flare is buried more than 1 to 2 inches, remove the excess growing medium to expose the flare areas prior to planting.

Fig. 32 - Vertical slices through a pot-bound root system encourages more radial root development.

Inspect balled-and-burlaped or tree-spaded trees for soil depth over the root collar flare using a wire probe. If there is more than 1 to 2 inches of soil over the flare/branch root area, plant the tree higher than normal in the landscape, remove the excess soil prior to back-filling the planting hole, and inspect the stem for developing encircling roots or SGRs. Consider rejecting trees that are deeply buried within the root ball. Use the height of the root ball versus the depth within the root ball to the lateral roots as a guide. The more deeply buried the root system, the fewer roots available for tree establishment.

Fig. 33 - An alternative to slicing and removing roots is simply straightening them out prior to planting in a sufficiently wide planting hole.

If the root collar flare and stem are above the soil surface, developing SGRs will be easily detectable and treatable long before they cause physiological stress to the tree. Therefore, prevention of SGRs must include planting trees so that the root collar flare is at or only slightly below the soil or mulch surface.

Treating Trees With SGRs
Removal is the most common treatment of encircling roots or SGRs that have caused minimal stem compression. Roots may be removed with wood gouges, saws, or pruners during the examination process (Figures 34).

When SGRs have caused extensive stem compression and are fully or partially embedded in the stem, modify the removal treatment to avoid damage to the stem. Embedded and severely compressing SGRs are often left in place when they cannot be safely removed; there is some belief that SGRs reduce the typically short life span of urban trees by only a few years, and the potential damage associated with SGR removal is not justified (Watson et al. 1990; Tate 1981). A compromise is to prevent the SGR from growing and further compressing stem tissues by severing it at the edges of the stem. Remove the remaining root to a distance where it no longer poses a threat to the stem and allow the severed SGR to decay with time. Annual examination of the stem to assess for decay is recommended.

Fig. 34 - Buried with 12 inches of soil during a construction project 15 years prior to this examination, this white oak had formed two SGRs.

The season during which SGRs are removed might influence the success of the treatment. Smiley (1999a) found that summer removal resulted in better diameter growth over two years than did fall removal or a combination of summer and fall removal for red maple trees under an irrigation system.

Fig. 36 - After this littleleaf linden was examined, the encircling and girdling roots were removed, as well as the twine. The sod was then removed farther out and the area was lightly mulched. This tree continues to be periodically monitored, but should live a long and healthy life.

Regardless of treatment, do not backfill the examination area. Lightly mulch the exposed roots but not the root collar flare or stem area (Figure 36). Subsequent examinations will not require the time-consuming removal of soil.

Treat the tree to improve vitality or at least reduce environmental stresses during the recovery period if SGRs are removed, or as long-term maintenance if SGRs are prolific and imbedded. Maintain optimum soil water through irrigation and surface mulches. Surface mulch as much of the rooting area as possible, but do not pile mulch against the tree stem or completely bury the exposed root collar examination area. Mulch also helps to remove competition for water and nutrients from turf grass.

Control infectious diseases and insect pests, especially those that defoliate canopies or induce stem cankers. Nutrients may be added if soil and/or a foliar analysis indicates a deficiency.

There are instances where the treatment options include removal. If stem compression from SGRs is severe and extensive (greater than one-third to one-half of the stem circumference), tree stability might be the main issue. Consider removing SGR-affected landscape trees that pose a high risk of failure and are near immobile targets (e.g., sidewalks, buildings, streets). In other instances, planting new trees near SGR-affected trees in anticipation of their death would be appropriate.

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