A Venturi Effect Can Help Cure Our Trees

Summary

Compared to the more traditional hole-based methods, most of which require the tree to be drilled, tools with lenticular blades transform the basics of endotherapy easing the closure of the wound and allowing the natural uptake of the solutions.

Abstract

In woody plants, xylem sap moves upwards through the vessels due to a decreasing gradient of water potential from the groundwater to the foliage. According to these factors and their dynamics, small amounts of sap-compatible liquids (i.e. pesticides) can be injected into the xylem system, reaching their target from inside. This endotherapic method, called "trunk injection" or "trunk infusion" (depending on whether the user supplies an external pressure or not), confines the applied chemicals only within the target tree, thereby making it particularly useful in urban situations. The main factors limiting wider use of the traditional drilling methods are related to negative side effects of the holes that must be drilled around the trunk circumference in order to gain access to the xylem vessels beneath the bark.

The University of Padova (Italy) recently developed a manual, drill-free instrument with a small, perforated blade that enters the trunk by separating the woody fibers with minimal friction. Furthermore, the lenticular shaped blade reduces the vessels' cross section, increasing sap velocity and allowing the natural uptake of an external liquid up to the leaves, when transpiration rate is substantial. Ports partially close soon after the removal of the blade due to the natural elasticity and turgidity of the plant tissues, and the cambial activity completes the healing process in few weeks.

Introduction

In recent times, trunk endotherapy has progressively replaced traditional air spray methods in woody plants^1-6, but this is not a recent idea. In the 15^th century Leonardo Da Vinci described in detail how he was able to intoxicate apples by injecting arsenic solution into the trunk of an apple tree through deep holes made with a gimlet⁷. Little has changed since then: chemicals easily available in nature have gradually been replaced with more efficient synthetic active ingredients (insecticides, fungicides, bactericides, fertilizers, plant growth regulators and desiccants). Atmospheric pressure injections evolved into high pressure, an....

Protocol

1. Perform treatments preferably between bud break and late summer, in sunny and breezy days, according to general rules in tree endotherapy¹⁷.
2. Wear gloves, protective glasses and any other safety device according to regulations in force.
3. Get familiar with the instrument, disassembling and reassembling it. Its main components are reported in Figure 2.
4. Get familiar with the method, described in the following steps and in Video 2. Start practicing infusion technique using water in an un-pruned tree with smooth bark, fully developed canopy and very broad leaves (i.e. Platanus spp., Quercus

Results

Due to its small dimension and unique shape, the lenticular blade does not remove cambial and woody tissues, and when compared with traditional drill holes, the wound is visibly smaller (Figure 4a). Usually, the edges of the hole are slowly compartmentalized by cambial tissues (Figure 4b1), often because of overheating during drilling. Conversely, after treating the same tree with a lenticular blade, the woody fibers revert to their previous shape, and the cambium starts to produce meris.......

Discussion

In spite of the acknowledged environmental advantages of tree endotherapy, up to now the main factor limiting a wider spread of this method has been related to the negative side effects of the drill holes used in traditional pressure methods (i.e. delayed wound closure, parasitic infections through the hole, production of inactive discolored wood).

In contrast with other methods, the described one was envisaged to work in compliance with host physiology, considering the delivery rate .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
BITE	Vitzani srl, Perarolo di Cadore, Italy