   Treating Wounds of Trees and Shrubs - September 7, 2011 Jeff Schalau, Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County Gardeners want to do the absolute best for their plants – especially when a limb has been broken or the bark has been accidentally damaged. Others have learned that pruning wounds should be sealed with a pruning compound to “protect” the plant from insects and pathogens. However, scientific research tells us that pruning compounds and sealants actually do more harm than good when applied to plants (with one exception which I will mention later). Claims made by the manufacturers of these products are horticulturally untrue even if their claims to inhibit rust, seal roofs and rain gutters may be well founded. Woody plants have developed their own processes for mitigating damage and preventing the entry and spread of rot causing fungi and bacteria. Coniferous trees produce resin (pitch) which seals surface wounds. Most trees also deposit rot resistant phenols, tannins and other compounds into the heartwood to increase rot resistance internally. Each year, trees form hundreds of tiny abscission layers as leaves senesce and fall. Wounds left from branch breakage are callused over and compartmentalized within the trunk to prevent the spread of rot causing organisms. All of these processes occur without human intervention. Trees do not heal. Instead, they naturally isolate damage through formation of suberized, lignified wood that physically and chemically repels invasion. Suberin is produced in cell walls to make cells less permeable to water (like cork) and lignin is a complex chemical that hardens cell walls. Callus tissue develops at the edges of a wound and gradually expands towards the center. This wound wood remains for the life of the tree (although it may be covered by subsequent growth); bark does not regenerate itself the same way our skin does. Wound dressings/tree sealants initially trap moisture and create an ideal environment for decay. Over time, they inhibit compartmentalization, prevent wound wood (callous) from forming, and eventually crack, again exposing the tree to pathogens. Some of the “natural” products that use non-petroleum based formulations can also serve as a food source for pathogens. Many arborists claim there may be some benefit in applying sealants to tree wounds in species particularly susceptible to certain diseases, such as oak wilt and Dutch elm disease. Many regions in the country specify that oaks pruned in areas where oak wilt is a problem should be treated to prevent infection. While research supporting this advice is questionable, it may be justifiable to use a fungicide or insecticide during spring or summer pruning. If pruning is done during the dormant season, chances of infection are greatly reduced and wound treatment should be avoided. In addition, oak wilt and Dutch elm disease are not known to exist in Arizona. The one exception where pruning sealers are recommended is on freshly pruned rose canes. Rose canes have very soft, relatively large diameter pith (soft tissue in the center of the cane). This tissue is very attractive to carpenter bees, solitary wasps, and sawflies. These insects bore into the pith of the cane creating physical damage, potential entry points for disease, and sometimes plant mortality. The simplest solution is to cover the freshly cut rose cane ends with waterproof white glue. This usually prevents entry of these boring insects and their subsequent damage. Plants have natural mechanisms to fight insect attack or disease. Covering wounds with traditional sealants inhibits oxidative processes, which in turn reduces callus formation and subsequent compartmentalization. Prune susceptible woody plants during fall and winter when insect and disease activity is reduced or absent. Sanitize pruning tools with 70% isopropyl alcohol or a 9:1 water to bleach solution. This can help reduce the transmission of certain plant diseases to healthy plants. Use preventative techniques to manage disease through practices such as proper irrigation, disposal of contaminated material, and use of disease-free compost and mulch. Much of the above information was excerpted from Linda Chalker-Scott’s Horticultural Myths website (see link below). You can also see Linda Chalker-Scott speak at the Arizona Highlands Garden Conference (AHGC) in Prescott October 22, 2011. Call the Prescott office of Yavapai County Cooperative Extension at 928-445-6590 for more information about the AHGC. Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener line in the Camp Verde office at 928-554-8999 Ext. 3 or e-mail us at cottonwoodmg@yahoo.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener line in the Camp Verde office at 928-554-8999 Ext. 3 or e-mail us at cottonwoodmg@yahoo.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. Link to Linda Chalker-Scott's Horticultural Myths Website www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/  |