Diagnosing Drift and Carryover Injury in Nursery/Landscape Trees

Drift and carry-over injuries, by nature, involve sub-lethal dosing from pre- and post-emergence herbicides. These can be difficult to diagnose often manifesting as long-term impairments. Short-term injuries are catastrophic; however, long term injuries are chronic such as disrupted acclimation, reduced hardiness, reduced nutrient uptake, and weakened tissue integrity. An overview of several carry-over and drift herbicide injuries will be presented but special attention will be given to studies with Acer x freemanii ‘Jeffersred’, Malus ‘Prairifire’, Cercis canadensis and Quercus rubra. These studies revealed if root shank suckers were removed mechanically or razor blade incisions were made near the tree crown the incidence of bark cracking increased versus no injury. If low dose basal applications (BA), to stimulate drift, of Roundup Original Max^® (48.7% potassium salt of glyphosate) (highest) or Roundup Pro^® (41% isopropylamine salt of glyphosate) (second) were made near the crown, but not directly applied, following wounding significantly more cracking occurred with Acer x freemanii ‘Jeffersred.’ The sprays were conducted in spring and cracking was measured as a carry-over injury the following spring. Of the four remaining treatments only the no wound/no herbicide control was statistically lower than the other three, wound/no herbicide, wound/KleenUp Pro^® (41% isopropylamine salt of glyphosate) and wound/Scythe^® (57% pelargonic acid). Detached current year shoots were frozen in a controlled ultra-low freezer and evaluated. Significant decreases in cold hardiness, over species, occurred in shoots, eight months after BA of Roundup Original Max^® and Roundup Pro^®. The no wound/no herbicide control had the hardiest shoots, followed by the wound/no herbicide and wound/KleenUp Pro^® which were not statistically different. On November 2, 2011 (fall) and June 25, 2012 (summer), AquaMaster^® (53.8% isopropylamine salt of glyphosate) and Roundup Pro^® were sprayed over-the-top (OTT) or as BA applications, directed 2.5 in from crown/substrate union to simulate drift versus a direct application on Syringa reticulata. Shikimic acid (SA) levels (as a real time biomarker for determination of plant exposure to glyphosate), were quantified by leaf tissue extractions and LC/MS/MS evaluations following treatments. SA levels in leaves following summer and fall + plus summer applications of Roundup Pro^® OTT increased 17.5 fold and 10.2 fold, respectively, versus the control, indicating a long-term carry-over effect on the SA pathway. Specific glyphosate formulations carry-over in the plant, result in long-term disrupting of the SA pathway, reducing cold hardiness, and increasing frequency of bark cracking in susceptible species.