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PLANT HEAL ANT HEALTH CARE Movin'On Up U Understanding uptake and translocation of chemicals By Br andon Gallagher Watson nderstanding the uptake and translocation of chemicals within trees is important for arborists wanting to effectively treat trees for insects and diseases.But how much do we need to know to be effective? Tree physiologists study how chemicals are absorbed into the vascu- lar system and the roles various enzymes and metabolites play in transporting those chemicals throughout the tree.For you, the practical arborist,understanding uptake needn't be as concerned with the molec- ular level as the physiologist, but we can take concepts from them and use them to better understand how applications are getting into the tree and moving within them. The term "uptake"refers to treatments being absorbed into the tree through various parts of the tree — most commonly though the roots, bark, foliage or by injection.Translocation, then, is the movement and distribution of those chemicals within the tree.Many factors affect the speed at which uptake and translocation occur,including molecular size, solubility, time of year,water availability, tree anatomy and tree health. Similarly, these factors affect the translocation of the chemicals within trees,as does the volume of water with which they are applied and where on the tree they were applied. Probably the most important thing for arborists to know about uptake relates to what factors will affect the speed at which the treatments are effective. Regardless if the treatment was applied by tree injection or soil application, uptake and distribution of chemicals is reliant upon the tree's vascular system.Within the vascular system,water and nutrients are absorbed through the roots and transported up to the foliage by the process known as transpiration.This mechanism is the result of the cohesion properties of water.You know how you can float a paper clip on top of water? That's because the hydrogen atoms in water mole- cules are attracted to each other like a magnet. As water molecules exit the top of the plant through the leaves, the cohesion properties of water pull the next molecule into its place.From the tip of the leaves to the tip of the roots, all the water molecules in a tree are connected and keep moving up as the next one exits. Arborists can take advantage of this upward pull to apply treatments to a small proportion of the tree and have that treatment moved inter- nally to other parts of the tree.This what "systemic" treatments are doing,and they can be applied to trees in many different ways, includ- ing through the roots, the bark, the foliage, and injected directly into the vascular system. 18 Arbor Age / September 2012 Transpiration moves water and treatments up. All photos provided by Rainbow Treecare Scientific Advancements Soil-applied treatments Soil-applied treatments enter the tree through the roots, and are the most common systemic treatments used by arborists.It is the fine fibrous roots that are primarily responsible for uptake,so it is important to target your applications to reach a high number of those fibrous roots. Even as recently as five years ago,many soil-applied treatments,includ- ing imidacloprid,came with the recommendation of applying in a grid pattern within the dripline of the canopy.There were issues with timing and predictability with this method. First, tree roots come off the trunk in,more or less,a spoke pattern like the wheels on a bike.Applying in a grid manner means some of your application may be in between those spokes and not enter the tree at all. Second, a treatment that entered a root 20 feet from the trunk means it has to move 20 feet just to get to www.arborage.com