A complete guide to vascular injection: choosing the bore site, calculating the dose and caring for the tree afterwards.
When a tree stands 20 metres tall and its canopy covers several hundred square metres, effective spraying is simply not achievable. Even with the best equipment much of the solution never reaches the upper canopy, and what does arrive is quickly washed off or degraded. Trunk injection was designed for exactly this class of problem.
The underlying principle
A tree's xylem is the pathway carrying water and dissolved minerals from root to leaf. Transpiration keeps that pathway working like an active pump. Introduce the active compound into it and the tree itself distributes the material throughout the canopy — with no need for us to physically reach the upper branches.
How the operation runs
- Tree assessment: identify the causal agent and check trunk condition. A tree with extensive trunk decay is not a suitable candidate.
- Dose calculation: based on diameter at breast height (DBH). A larger tree has greater xylem volume and therefore takes a higher dose.
- Drilling: at a defined height above ground, with a clean bit at a standard diameter. Depth must reach active xylem without passing through it.
- Fit and inject: the pressurised capsule is fitted and left until it empties. Emptying time depends on weather and transpiration activity.
- Seal the entry: close the point with a dedicated paste to keep pathogens out.
Timing
The best window is when transpiration is active but the tree is not under severe stress. Late spring and early summer mornings usually offer the best conditions. Injecting on very hot days, or in the middle of the day when stomata are closed, sharply reduces uptake rate.
Which trees?
The method is designed for trees with a sound trunk of adequate diameter. Young trees with slender trunks, trees with extensive decay, and species that gum heavily are generally poor candidates. Plane, elm, walnut, date palm, pine and oak, by contrast, respond very well.
Does it harm the tree?
Any hole in a trunk is a wound and there is no point pretending otherwise. But when drilling is done at standard diameter and depth with clean tools, a healthy tree callouses over completely within one or two growing seasons. Set against that, the cumulative damage of years of spraying to soil, groundwater and beneficial insects is far greater.