Effect of Postemergent Herbicide On Sucker Removal/Injury of Field Tree Liners

Researchers at OSU have speculated that increased bark cracking in the nursery industry is due to the use of glyphosate products containing increased surfactants.  The objectives of this study include:  1) To determine if various forms of glyphosate-containing products increase incidences of bark cracking. 2) To evaluate cold hardiness of trees subjected to various glyphosate-containing products.  At The Ohio State University, Columbus, OH, four species of tree liners were planted in the field on October 5, 2003.  The species evaluated were: Acer x freemanii ‘Jeffersred’, Malus ‘Prairifire’, Cercis canadensis and Quercus rubra.  The treatments were: Roundup Original, Roundup Pro, Kleen-up Pro, Scythe, mechanical, and a control.  Trees had suckers removed mechanically in June 2007 and 2008 via hand pruners for corresponding treatments.   Trees that lack suckers had an incision made 2.5 cm wide x 5 cm in length.  After injury was made, plots had corresponding herbicide treatments applied.  Cuttings were taken from terminal ends of shoots in January of 2008 and 2009 to assess cold hardiness.  The plants were then frozen at nine temperatures every 3^o C from -6 to -30^o C in an ultra low chest freezer (Forma Scientific, Inc., Marietta, OH).  There were three evaluation methods to determine cold hardiness: visual (amount of live tissue), starch (lugor stain), and electrical conductivity (EC).  Data from 2008 indicated maple showed the greatest number of cracks over all treatments.  This correlates with what is being observed within the industry.  Roundup Original and Roundup Pro exhibited the greatest number of cracks between all Genus of trees, while the Kleenup Pro and Scythe exhibited less cracks.  This could be attributed to the increased surfactant contained within the Roundup products.  The browning data indicated that control and mechanical treatments were significantly more cold tolerant than Roundup Original and Roundup Pro.  This is most likely due to the disruption of the shikimate pathway (Duke and Powles, 2008), decreasing phenolics; so therefore decreasing cold tolerance (Rivero et. al., 2001). All trees showed a decline in hardiness across all treatments as temperature decreased with the browning observations.  This study confirms Kuhns’ (1992) study that glyphosate injury produces cracking in trees.