Woody weeds are tough and persistent. Their persistent nature means that you need to use a programmed approach over three or more seasons to effectively control them. Different woody weed species often require different herbicides and application techniques for long term control.
The first step in any woody weed control program is to identify the weed species and growth habit in each paddock, then determine the infestation density. Once you have determined that the use of herbicides is the best tool in a particular weed control situation, you must then select the best herbicide for the job. The species, density and growth habit of the vegetation will dictate the application method(s) and herbicide (or mix thereof) that will achieve the required weed control outcome and help reduce the risk of off-target damage. Other considerations will be site and job specific.
This situational analysis will help decide whether the most appropriate application method is foliar application, basal bark treatment, cut stump or stem injection. Each method has advantages and disadvantages that are detailed in Dow AgroSciences’ Woody Weed Control Guide and their smart phone and tablet apps (the tablet app also contains demonstration videos). It is unlikely that any single application technique will sufficiently clear an area; a combination of methods will most likely be used together.
Using the herbicide that delivers the best efficacy almost always does so with the lowest rates of active ingredients and results in the least amount of regrowth and the lowest rate of re-treatment. That means less follow up in labour (which generally equates to 60+% of the overall cost) and herbicide.
For foliar spraying (high volume handgun application) a selective herbicide such as Grazon™ Extra is usually a better choice than one which is non-selective (such as the various glyphosate-based herbicides), unless any grasses present need to be treated at the same time. Use of a non-selective herbicide (like glyphosate) leaves the soil exposed and increases the risk of erosion as well as invasion by weed species. Even if a selective herbicide is chosen, the regrowth generally includes the same species as those outside the immediate treatment area, and good application practice is essential to minimise any risk of off-target damage.
Selectivity is less important when using stem injection, basal bark or cut stump application as the more precise method of application ensures minimal risk of off-target damage. However, when using basal bark or cut stump treatment, consider all aspects of the choice of carrier; how will it be transported, how will it be mixed, etc.
Worker health and safety considerations must also be considered with vegetation features. Products that are packaged in easy to manage containers, do not require mixing, and have minimal exposure to workers are preferred by all users, but especially within organisations with strict procedural guidelines.
Vigilant™ II Herbicide has been a breakthrough in this regard. It is available in an easy to manage 240mL gel that can be refilled from a 5L container via a handy pump. It is formulated as a gel which is applied as a paste directly from the pack; no mixing, no dripping, no exposure. In fact the label requires no personal protective equipment, not even gloves, though it’s always a good idea nonetheless.
Vigilant controls more than 49 weeds ranging from African boxthorn to wild tobacco tree; some profess “it kills everything”. With this degree of simplicity of use (particularly with regard to required paperwork) and efficacy, some councils and vegetation management companies are now only carrying Vigilant.
Irrespective of which aspect you review first (vegetation population and species, site considerations and worker safety) all should be deliberated prior to work commencing.