Injecting into a tree requires a drill and the penetration of the protective bark, the drill holes are spaced around the tree and chemical is then injected with measured injectors. This treatment is a great way to deliver a chemical quickly and efficiently into the trees vascular system, results are good and chemical use is less than with other methods.
The downside is the drill holes, there is nothing ‘micro’ about them, they are at least 4mm diameter and depending on species and age could be more than 4cm deep. Each treatment (every 2 – 5yrs for Elm Leaf Beetle) requires a new set of drill holes. A tree will usually callus (but not heal) over drill holes within a few years, particularly younger healther trees. This covering of the wound is good from an aesthetic perspective however the damage remains inside.
“The holes are an entry point for decay causing pathogens, also the tree will actively shut the area around the wound down, ceasing to function in that area. Over many years the number of holes will impact plant function.”
The degree of impact will depend on a number of factors, if a tree is old and stressed possibly in a cool climate, it will be less able to deal with pathogens, less able to compartmentalize decay, less able to callus over. A young fast growing tree in Queensland such as an avacado will quickly callus over and put on new conductive tissue.
For these reasons our approach to Stem injection for any pest or disease (including Elm Leaf Beetle) is that stem injections should only be used in certain circumstances; for example the tree is going to be removed in the short to medium term or it is not possible to use other control methods. Some companies are now doing more stem injections, though this may (not ‘will’, just ‘may’) give better Elm Leaf Beetle control in the short term, long term it will cause permanent damage and possibly significant decay within the trunk.
Sometimes it may be appropriate to use stem injection if there is an infestation and it is getting late in the year for soil injection.
- Moore G. M., 2004. Managing Aging Trees: Implications for Tree Health. in Smith K (Ed)
- Smith K.D., 2004. Amenity Tree Health: Pests & Diseases Workshop : Workshop Proceedings. Friends of the Elms, Burnley Campus, 2004
- Friends of the Elms, Melbourne