Stem injection herbicide treatments for controlling neem trees

Abstract

Azadirachta indica A. Juss, (neem trees) tolerate hot, dry conditions and have become widely invasive across northern Australia. To investigate more options to control this weed, a replicated trial was conducted to assess the control efficacy of stem injected herbicides. Using a cordless drill, ten herbicides were applied as either liquid solutions or encapsulated granules injected into the base of trees and a maximum rate of one injection per 15 cm of circumference. In each injection interval, one concentrated herbicide capsule or 2 mL of a concentrated liquid herbicide solutions (drill and fill) were applied. Three liquid herbicides solutions were highly effective (>98%). Two encapsulated herbicide
products were also >95% effective. These five treatments matched the efficacy of a reference basal bark treatment but used much less herbicide. The efficacy of other liquid or granular treatments was higher when injected at smaller circumference intervals, or in smaller trees. The trial data showed A. indica is controlled by multiple encapsulated herbicides and drill and fill liquid herbicide solutions. Stem injected herbicides are an effective and additional treatment option for individual A. indica trees.