Chemical treatments Herbicides are used widely in forestry to control weeds, mostly at establishment. To control weeds and avoid damage to tree seedlings, use the appropriate herbicide for each situation, at the right time and at the correct rate. Many chemicals used in farm forestry are not registered for forestry use. For 'off-label' use, obtain a permit from the National Registration Authority. Contact Chris Sharpe, Senior Chemicals Adviser in Agriculture Western Australia's Chemical Services Section for advice on permits.
Permits can take up to three months to obtain.
Knockdown and residual herbicides Knockdown herbicides such as glyphosate and amitrole kill existing weeds, but don't stop new weeds from germinating and growing. Residual herbicides such as atrazine and simazine work in the soil to prevent the germination of new weeds. Some residual herbicides also have a knockdown effect. For example, hexazinone is also a general knockdown, sulfometuron methyl becomes a general knockdown at higher rates, oxyfluorfen is a knockdown for specific weeds, and atrazine is an effective knockdown for newly emerged weeds. To kill existing weeds, and keep tree planting sites free of new weeds for a long period, mixtures of knockdown and residual herbicides are usually used.