For more than 30 years, Arbor Age magazine has been covering new and innovative products, services, technology and research vital to tree care companies, municipal arborists and utility right-of-way maintenance companies
Issue link: http://read.dmtmag.com/i/75905
All graphics and images provided by Rainbow Treecare Scientific Advancements Abscisic acid helps fight drought stress, and helps close the stomata when it is hot and dry. Gibberellin inhibitors reduce tree growth. tends to be produced by plants as a response to tough environmental conditions.Drought-stressed plants are stuck in a Catch-22 where they need their stomatas open to get the CO2 for photosynthesis,but if they are open too long the leaves lose too much water and scorch.To com- bat this, stressed plants produce abscisic acid to open and close their stomata throughout the day, letting enough CO2 in while not losing too much water.Abscisic acid also plays a role in stimulating fibrous root production,which further helps a stressed plant cope with adverse environmental conditions. Gibberellin The last major group of plant hormones is the gibberellins.Named for the fungus from which they were first isolated,there are currently about a 130 different gibberellic acid compounds found in plants, fungi and bac- teria.In plants,gibberellic acid plays many different roles depending on the specific gibberellic acid in question.It affects seed dormancy and also helps trigger flowering in response to daylight length.One of the major roles it plays is in cell elongation, similar to auxin,but with a different mode of action.Agriculture has found gibberellic acid to be a useful hormone for increasing the length of seed stalks to make them easier to mechanically harvest. Growth regulators Plant growth regulators (and tree growth and shrub growth regula- tors, for that matter) are the group of products available to tree care professional that can either increase or decrease a plant hormone for a desired effect. Growth regulators are an important revenue source for many tree companies and give arborists new options for tree care.Some may be employed just to reduce growth, some to increase growth, and others may be employed for a tree health care purpose.You may already be aware of products that affect plant hormones without realizing it. www.arborage.com Many growth regulator products are applied at the base of the tree. Sucker Stop is a product sprayed on new cuts to reduce sucker growth that will affect the formation of cytokinins and block cell division.Garden centers commonly sell Root Stimulator products for new transplants. These are small amounts of auxin applied to make root cells elongate. A product widely used in the arborist market is palcobutrazol (Cambistat,Profile).This product is applied to base of the tree,and when it translocates to the canopy it will block the formation of gibberellic acid. This results in a reduction of vegetative growth,which has many uses in tree care —from keeping trees out of power lines longer to keeping a subur- ban lawn tree at a reasonable size.It turns out that gibberellic acid is made from some of the same base compounds as other plant hormones such as abscisic acid.So by reducing the amount of gibberellic acid we are increas- ing the amount of abscisic acid.This slower-growing tree will be putting more energy into root production than shoot production, and with the increased abscisic acid,be more responsive to urban tree stress conditions. Treated trees show less scorch, and there are some dramatic examples of stressed trees brought back from the brink. As with all tree health care treatments,plant growth regulators are just another tool in the toolbox.However, if employed for the right reason can be just the tool you need.Knowing about plant hormones can give you a whole new way to affect the health of trees,can give you new busi- ness opportunities,and,of course,can make you incredibly interesting at your next dinner party. Brandon Gallagher Watson is director of communications at Rainbow Treecare Scientific Advancements,and is an ISA Certified Arborist (#MN-4086A). Watson recently discussed insects and diseases that are impacting trees as part of the latest Green Media Internet Broadcast.To listen to the interview, visit www.ArborAge.com and click on the "Internet Broadcast"link in the left-hand navigation bar. Arbor Age / July/August 2012 13