Little Leaf Linden: Treated with paclobutrazol, this tree displayed reduced symptoms of drought-induced leaf scorch compared to if left untreated.
turia inaequalis ) on crabapples ( Malus ‘Radiant’) and cytospora canker ( Leu- costoma kunzeii ) on blue spruce ( Picea pungens ). These improvements likely stem from the combined physiological and morphological changes induced by the treatment. Enhanced resistance to bacterial dis- eases has been observed as well. McIntosh apple trees treated with TGRs experienced significantly less fire blight ( Erwinia amylovora ), likely due to reduced tip elongation – and therefore less susceptible surface area – on treated shoots. Red oaks ( Quercus rubra ) infected by bacterial leaf scorch ( Xylella fastidiosa ) have also shown suppressed symptom development. Because bacterial leaf scorch symp- toms are closely tied to water stress , the increased drought tolerance asso-
both human error and worker expo- sure to risk. TGRs can help keep vig- orous species from obscuring signs or lighting and can reduce the need for pruning along roadsides – work that often places crews in high-risk envi- ronments. They also minimize ladder work on small, highly manicured trees, where workers typically use powered shears and face increased fall hazards. In many cases, these reductions trans- late directly into improved safety for crews and the public. WHY ARBORISTS USE TGRS: DROUGHT RESILIENCE The physiological and morphological changes triggered by TGRs – such as elevated abscisic acid, thicker cuti- cles, increased trichomes, and denser fine roots – add up to stronger drought
tolerance. Research also suggests that TGRs can support recovery following drought stress . And while drought is often associated with lack of rainfall, arborists know the problem is more complex. Compacted soils, heat-absorbing surfaces, poor in- filtration, and high soil temperatures frequently induce drought-like stress in urban and suburban settings. TGRs offer another tool for helping trees cope with the realities of these challenging sites. WHY ARBORISTS USE TGRS: DISEASE RESISTANCE TGRs also show promise for increasing disease resistance. Studies demonstrate improved resistance to several fungal pathogens , including apple scab ( Ven-
62 | Winter 2026 ArborTIMES ™
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