Weeds compete with trees for moisture, light and nutrients so effective weed control is essential for the survival and growth of young trees.
Mechanical methods
Cultivation gives only short-term weed control, and can actually make things worse. When used alone it rarely gives adequate weed control for tree establishment, especially against deep-rooted perennial weeds such as sorrel, kikuyu and couch grass. For best effect, use cultivation as late as possible before planting, and combine with herbicide treatments.
Scalping (or furrowlining) removes a strip of topsoil and its resident weed seeds, leaving a weed-free strip for tree planting. Possible disadvantages include:
• Risk of erosion, especially on very light sands.
• Increased risk of tree death from waterlogging in high rainfall areas.
• Weeds may re-establish from seeds blown onto the scalped strips.
• Trees may need fertilising because the topsoil (rich in organic matter and nutrients) is pushed aside.
Grazing reduces pasture bulk and seed load, reducing the amount of knockdown herbicide needed before planting. Allow the pasture to freshen up before spraying.
Mulch can be an alternative to chemicals or cultivation in sensitive environments. The cost of buying and installing mulch can double establishment costs.
Chemical treatments
Herbicides are used widely in farm forestry to control weeds, mostly at establishment. Pre-planting weed control is especially critical for eucalypts because options for later overspraying are limited and expensive.
Use the appropriate herbicide for each situation, at the right time and at the correct rate.
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 - though is damaging to legumes such as Acacia species. Oxyfluorfen is a knockdown for specific weeds, and atrazine is an effective knockdown for newly emerged weeds.
Spray perennial weeds before site preparation to avoid incorporating these weeds into the mounds (especially kikuyu, couch, sorrel, and dock). The best time to spray is between spring and late autumn, when perennial weeds are actively growing with healthy foliage. Spray at least 21 days before cultivation to allow sufficient translocation of the chemical throughout the plant.
Strip or spot spraying is preferred over broadscale spraying because less herbicide is needed per hectare and there is less risk of erosion, insect attack and movement of herbicide from the site. Spray strips at least 1.5 m wide with a boom spray, or spray spots at least 1.5 m diameter where trees will be planted.
Application rates vary with the type of soil (heavy or organically rich soils need higher rates), the weed species and stage of development (large plants need higher rates), and the susceptibility of the tree species to the herbicide. Application rates must comply with the label, or a permit (for off-label use). Consult a farm forestry adviser to discuss suitable spray rates.
Economics of second year weed control
Second year weed control can increase tree growth, but is only economic if the extra growth offsets the cost of the operation, or if needed to ensure the trees' survival. It could be worthwhile for trees that have grown poorly in the first year, on sites with prolific weeds.
Careful grazing with sheep is a cheap and effective way to control weeds in the second year.
Extract from TreeNote No. 20 (May 2005) produced by Department of Agriculture, Western Australia
Weed control in eucalypts and pines in the greater than 450 mm rainfall zone of Western Australia
Mechanical methods
Cultivation gives only short-term weed control, and can actually make things worse. When used alone it rarely gives adequate weed control for tree establishment, especially against deep-rooted perennial weeds such as sorrel, kikuyu and couch grass. For best effect, use cultivation as late as possible before planting, and combine with herbicide treatments.
Scalping (or furrowlining) removes a strip of topsoil and its resident weed seeds, leaving a weed-free strip for tree planting. Possible disadvantages include:
• Risk of erosion, especially on very light sands.
• Increased risk of tree death from waterlogging in high rainfall areas.
• Weeds may re-establish from seeds blown onto the scalped strips.
• Trees may need fertilising because the topsoil (rich in organic matter and nutrients) is pushed aside.
Grazing reduces pasture bulk and seed load, reducing the amount of knockdown herbicide needed before planting. Allow the pasture to freshen up before spraying.
Mulch can be an alternative to chemicals or cultivation in sensitive environments. The cost of buying and installing mulch can double establishment costs.
Chemical treatments
Herbicides are used widely in farm forestry to control weeds, mostly at establishment. Pre-planting weed control is especially critical for eucalypts because options for later overspraying are limited and expensive.
Use the appropriate herbicide for each situation, at the right time and at the correct rate.
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 - though is damaging to legumes such as Acacia species. Oxyfluorfen is a knockdown for specific weeds, and atrazine is an effective knockdown for newly emerged weeds.
Spray perennial weeds before site preparation to avoid incorporating these weeds into the mounds (especially kikuyu, couch, sorrel, and dock). The best time to spray is between spring and late autumn, when perennial weeds are actively growing with healthy foliage. Spray at least 21 days before cultivation to allow sufficient translocation of the chemical throughout the plant.
Strip or spot spraying is preferred over broadscale spraying because less herbicide is needed per hectare and there is less risk of erosion, insect attack and movement of herbicide from the site. Spray strips at least 1.5 m wide with a boom spray, or spray spots at least 1.5 m diameter where trees will be planted.
Application rates vary with the type of soil (heavy or organically rich soils need higher rates), the weed species and stage of development (large plants need higher rates), and the susceptibility of the tree species to the herbicide. Application rates must comply with the label, or a permit (for off-label use). Consult a farm forestry adviser to discuss suitable spray rates.
Economics of second year weed control
Second year weed control can increase tree growth, but is only economic if the extra growth offsets the cost of the operation, or if needed to ensure the trees' survival. It could be worthwhile for trees that have grown poorly in the first year, on sites with prolific weeds.
Careful grazing with sheep is a cheap and effective way to control weeds in the second year.
Extract from TreeNote No. 20 (May 2005) produced by Department of Agriculture, Western Australia
Weed control in eucalypts and pines in the greater than 450 mm rainfall zone of Western Australia