Methodologies for weed control vary in terms of the target species being controlled or the nature of the site that the species is found growing in. Often manual methods of removal can be very effective but are often hard work, time consuming and impractical when faced with a significant area of a target species.
The use of herbicides needs a high degree of planning to ensure that the best result is obtained by their use and that the effects of their use is managed appropriately. There are also often rules and regulations set out in Pest Plant Management Strategies and Regional or Reserve Management Plans. If you are planning weed control in a wetland area in the Waihola Waipori Catchment it pays to check what type of chemicals are allowed to be used in that area with the Otago Regional Council or the Clutha District Council. If you would like further advice you are welcome to contact the Lake Waihola Waipori Wetlands Society also.
Foliar Treatment
Use commercial herbicides at prescribed label rates. Roundup (Glyphosate) at 1% or Gallant (haloxyfop) at 0.5% to treat Glyceria maxima.
Full foliar cover is required to kill plants and hand-held or back-pack sprayers will only be effective on small-scale applications. Foliar treatment is best used on grasses and herbaceous weeds
Basal Bark Spraying
The basal bark method is used for controlling woody weed species like willow and alder. It is extremely effective on woody plants with a stem diameter up to 15 cm’s. The advantage of the method is that it can used at most times of the year except when stems are wet or frosted. To be successful application should be made on all stems from ground up to about 40-50 cm’s. Effectively what you’re doing is chemically ringbarking the tree. It’s very important that you use the knap-sack or sprayer at relatively low pressure (20-40 psi) and prevent splashing of the chemical off the stems onto non target species adjacent to the target. The back-pack or sprayer should have a straight stream or cone shape to ensure effective cover and limit splashing. The method is not as effective on trees with thick bark. For these use the cut stump, frilling or drilling and filling methods
Use 1 part Grazon (Triclopyr butoxyethylester) mixed with 4 parts basal oil (20% solution). If you require a dye to mark controlled plants you can use white, oil-based enamel paint at 250mm per 5 litres. Be patient, it may take up to 18 months for the treated trees, shrubs or vines to die depending on the size and efficacy of application.
Frilling
Frilling is used for woody plants that have a stem diameter greater than 15cm’s. Using a hatchet make a uniformly spaced, series of overlapping cuts around the base of the stem being careful not to ring-bark the tree as this will stop the uptake of the applied herbicide through the stem. With the axe angled make the cuts downwards, going through the bark into the sapwood and then spray the basal bark herbicide mix all around the stump just above the frills so it runs down into the cuts. Use 1 part Grazon (Triclopyr butoxyethylester) mixed with 4 parts basal oil (20% solution).
Cut Stump Method
The cut stump method can be used for smaller trees or shrubs. Using a loppers or a hand saw cut the stems off as close to ground level as possible. Once the cutting is completed immediately apply basal bark herbicide mix to the cut stump surface, especially the outer edge as well as the remaining bark. The effectiveness of this method is greatly reduced if there are delays between the cutting and the chemical application. This method can be used at most times of the year but is most effective during the active growing season. With the cut stems its vital that you prevent the branches from contacting the ground because they will re-root themselves by layering. This is especially applicable to willow. The use of a piece of polythene or old plastic tarpaulin is quite useful to lie the cut material on and preventing it having direct ground contact.
Drilling
The drilling method can be used for large trees. You need to drill 30mm deep holes no greater than 50mm apart around the base of the tree using a 15mm drill bit. It’s your choice if you use a hand drill or a rechargeable drill but if you’re doing a large number a rechargeable drill is probably better. The spacing of the holes around the trunk of the trees is critical to the success of the drilling technique. The holes should be drilled as close to vertical as possible so that the herbicide stays in the tree. On completion of each hole immediately inject the properly measured dose of herbicide. Wait until the liquid subsides and then apply the remainder of the required dose. This technique is best undertaken in late summer early autumn. It’s quite a labour intensive method and you may find that frilling is a quicker option in large areas.
Health and safety
When undertaking any weed control work the health and safety of your contractors, staff and volunteers is imperative. Personal Protection Equipment (PPE) is essential during any chemical application or manual removal. That means using the recommended PPE equipment while handling or applying the chemical you have chosen to use for your weed control programme. The Safety Data Sheet of your chosen chemical will provide you with information on handling, storage, and personal protection. If you have any doubts about the safe use of chemicals in weed control you should talk to others who have experience in their use or you might consider attending a Growsafe course.
Lake Waihola Waipori Wetlands Society 