Organic producers are not allowed to use synthetic pesticides in their production system. However, herbicides derived from natural sources may be allowable. Interceptor is a non-selective, contact herbicide derived from an extract of pine oil. Since the herbicide kills by contact, uniform spray deposition on the target plant is required for maximum efficacy. An evaluation of the effectiveness of this herbicide can be found at
Many organic gardeners prefer to use homemade weed killer recipes so here are two to try:
- Put ½ cup of salt in a spray bottle and fill with 4 litres of white vinegar. Add a squirt of liquid dish soap to act as surfactant. Use early in the morning on a hot day as it works best in the heat.
- Or combine 4 litres of 10-20% pickling vinegar with 60ml. orange oil and a squirt of dish soap. This is claimed to kill any plant and again works best on a hot sunny day. It is suggested wearing rubber gloves.
Don’t leave the mixture in your sprayer for long because it will corrode the seal so wash the sprayer thoroughly after use. The mixture can be placed on a sponge and wiped on the plants you want to kill. While the acetic acid in the vinegar will start working immediately, some weeds will have to be treated again. One advantage is that new plants can be planted the next day after treating the weeds.[/vc_column_text][vc_column_text]Cut stump application is where the plant is cut off completely at its base (no higher than 15 cm from the ground) using a chainsaw, axe, brush cutter or machete. A herbicide solution is then sprayed or painted onto the exposed surface of the cut stump emerging from the ground, with the objective of killing the stump and the root system.[/vc_column_text][vc_column_text]Stem scraping also called bark stripping or stem painting is used for plants and vines with aerial tubers. A sharp knife is used to scrape a very thin layer of bark from a 10 cm section of stem. Herbicide is then immediately applied to the exposed soft underlying green tissue.
The wick application method uses a wick or rope soaked in herbicide from a reservoir attached to a handle to wipe or brush herbicide over the weed.
For up to date chemical products listed for a particular weed the Agricultural Pesticides and Veterinary Medicines Authority (APVMA) website provides an excellent search engine. Simply type the weed you are interested in controlling in the ‘disease/pest’ search field and hit search. The search will bring up all the products and their labels to help you determine the rate of chemical required for the job at hand. https://services.apvma.gov.au[/vc_column_text][vc_column_text]However, research has shown that vinegar with 20-30% or more acetic acid concentrate works differently. If the ground surrounding difficult weeds is saturated with this strong vinegar, it will lower the soil PH to levels as low as 3, which stops anything growing. Microbes and soil biota will be safe and will go dormant until the PH comes back to normal over time, unless lime is added to speed it up.
Acetic acid acts as a desiccant, burning the leaves, drawing out moisture and destroying the plants’ cell membranes. The leaves, stems and any other plant part it reaches will immediately die by simply drying and shrivelling up.[/vc_column_text][vc_column_text]Use caution with all chemicals, handle carefully and don’t get any in your eyes. Any acetic acid concentration over 10% will also burn skin, and be especially dangerous to eyes. This harsh vinegar should only be used with tough weeds that are away from growing areas such as blackberry.
Many herbal and plant oils contain natural pesticide and herbicide properties. They can be mixed with other substances such as vinegar and soap to safely eliminate weeds. These oils are often found in organic preparations in garden shops, and include d-limonene, or citrus oil extract, Neem oil, castor oil, pine oil, cinnamon, clove and thyme oil. Cinnamon for example contains eugenol, a particularly potent herbicide. Dribble the mixture onto the weed so that it coats and smothers it.
Corn gluten is a pre-emergent weed killer and is a natural by-product of processing corn or maize into corn meal. It has an oily coating and inhibits the formation of roots. It does not harm existing plants and as a bonus has high nitrogen content, so it feeds your soil as well.
In early spring and again late summer if necessary, sprinkle over the area where weeds were or you know there are unwanted seeds. Use according to packet instructions or at 1 kg per 9.30 square metres. Wait 6 weeks before the corn gluten has completely broken down before you sow desirable seeds.[/vc_column_text][/vc_column][/vc_row]