c-ray
10-14-2006, 09:09 PM
A SWEET END TO WEEDS
by Margrit Beemster
Sugar has the potential to control annual weeds according to recent research trials conducted by researchers from Charles Sturt University.
The researchers, ecologists Dr Suzanne Prober, Dr Ian Lunt and Dr Kevin Thiele, have applied sugar to trial plots for a project funded by the NSW Environmental Trust on how to restore understorey species in endangered Grassy White Box Woodlands.
Trials on a private property “Windermere”, and a travelling stock reserve “Green Gully” near Young in central NSW have provided dramatic results, with Paterson’s Curse and Wild Oats flourishing in untreated plots whilst plots treated with sugar had far fewer annual weeds.
The researchers have found that sugar provides a good, short-term non-chemical and ecologically friendly method of weed control.
“It appears sugar is a tool we can use to help change a system back to one dominated by native species rather than weeds,” says Dr Suzanne Prober who has been working to conserve and restore grassy white box woodlands for the past 15 years. Nearly all of the woodland belt, from southern Queensland to northeast Victoria is now used for agricultural purposes, principally wheat and sheep.
So why does the sugar work?
Because it is one of the fastest ways of reducing soil nitrate levels.
Dr Prober’s compared soil nutrients in undisturbed woodlands and disturbed, degraded sites. She found the most striking difference between the two was in nitrate levels, which were extremely low in undisturbed remnants and high in degraded remnants.
“It seems that many of our weed problems are due to high nutrient levels”, says Dr Prober. “There is an enormous amount of information on how to increase soil nitrogen to improve crop growth, but very little on doing the reverse. However there has been some research done overseas where sugar was used to tie up nitrogen levels for a short time.”
The researchers, who spread half a kilogram of refined white sugar to each square metre of soil every three months, found this inhibited weed growth of most annual weeds giving the native plants the opportunity to become well-established. However more research is required to work out the optimum rate of application.
“We realise that the sugar levels we used in our trials would not be economic to use over broad scales”, said Dr Prober, “but at the moment we don’t know if we would get similar results if we used less sugar or if we used cheaper alternatives such as molasses or sawdust”.
So how does sugar reduce soil nutrients?
“When sugar is spread on the soil, it feeds soil micro-organisms, which then absorb lots of soil nutrients as they grow,” explains Dr Ian Lunt from CSU’s Institute for Land, Water and Society.
“The micro-organisms then hold these nutrients so the weeds can’t gobble them up. In effect we are ‘starving’ the weed species that require lots of nutrients to grow.”
The lack of nutrients stopped the weeds from growing large, allowing the native plants, which can grow well in low nutrient levels, to grow bigger and faster.
The trial plots are now in their fourth year and the researchers believe that as the native grasses they have sown grow large enough, they will be able to lock-up the nutrients in their roots which will keep the weeds in check in the long run. Early results have indicated that nitrate levels are starting to drop in the plots with well established kangaroo grass.
“We see what we have done so far as only part of the picture,” says Dr Prober. “There are a number of directions we would like to go. One of our Honours students, Lisa Smallbone, is looking at whether sugar helps us to re-introduce native wildflowers into degraded sites. If the wildflowers establish well, we want to find out if they contribute to weed control and soil nitrogen cycling later on. Our long term goal is to get the native diversity back into the understorey by working out the best method to re-establish a native ecosystem that is self-sustaining and resistant to invasion by weed species.”
Using sugar as an organic weed control, to help to restore endangered woodlands and native grasslands, is an innovative alternative to using herbicides.
“Herbicides are difficult to use in many remnants because they kill the native plants you are trying to save as well as the weeds,” says Dr Lunt. “Sugar does not have this undesirable effect. Herbicides also don’t reduce the soil nitrate as sugar does, which is the underlying reason for the flourishing weeds – they control the symptoms, not the cause. Sugar may also be a useful way to control weeds that grow near other endangered native plants.”
While the researchers are primarily interested in using sugar as a tool to help restore the understorey species in grassy box woodlands, they are aware their research could be the basis for other more agriculturally driven research.
“Broad leaf weeds such as Patersons’ Curse are the bane of every farmer’s life. Once infestations get very bad, it gets very difficult to control them,” said Dr Lunt. “Sugar may help land managers to control broad-lead weeds and to re-introduce perennial grasses in many places across the region. In particular, it could be a really helpful tool in organic farming or in places where herbicides are difficult to apply.”
Conservation Management Networks
Dr Suzanne Prober’s passion to conserve Grassy Box Woodlands was the inspiration and driving force behind the establishment of the Grassy Box Woodlands Conservation Management Network in 1998.
The network, which now has 682 members including 355 private land managers, local governments and Rural Land Protection Boards, was the first in Australia. There are now seven such conservation networks helping to conserve fragmented ecosystems in NSW and Victoria. The Grassy Box Woodlands Conservation Management Network is now managed through the Department of Environment and Conservation (DEC) in NSW.
When Suzanne, as a researcher with CSIRO, first began looking for woodland remnants 15 years ago, she found that there were no large, undisturbed areas that could adequately represent the woodlands in a National Park.
“What we have instead are little bits and pieces, scattered across three states, and each bit is important for different reasons,” says Suzanne who spent a year searching for remnants on private and public land.
“There might be a travelling stock route that’s really important because of its big trees or a little cemetery that has got the best native understorey and is the only place where some native plants still grow.” One such cemetery is at Monteagle, in central NSW, where Suzanne is conducting the only long-term fire frequency experiment in the native grassland ecosystems in southern Australia.
The Network, now coordinated by Toni McLeish, has its own newsletter “Woodland Wanderings” and has a number of goals including protecting remnants and supporting best-practice management. Sites have been protected by various means including legal protection via covenants and listings on local environmental plans; purchase by the Australian Bush Heritage Fund; or as Suzanne says “some sites just have a really interested owner who wants to try and do the right thing.”
“We tried to create a network that brought together all these disparate sites into what we called a ‘conceptual reserve’ with many different tiers, but with a link between them all,” explains Suzanne.
“I still see it as early days and the concepts will evolve. Since we established the Network a lot of things have happened in the landscape, but at the time we felt we had to make something actually happen on the ground rather than just “monitoring the decline.
“Fundamentally, the conservation management network aims to help landholders and site managers, which is the most important step we can make. It provides great information to help us all to learn from everyone’s experiences, and it demonstrates to everyone how their individual actions are helping to save one of Australia’s most endangered ecosystems, grassy box woodlands.” - Margrit Beemster
Hints for Establishing Understorey
The research being carried out by Dr Suzanne Prober and her colleagues may well provide answers for land holders and managers who find the management of weeds a problem in tree plantations and sites that have been fenced off to allow for natural regeneration.
“What we tend to do these days is fence off an area and plant trees in it,” says Suzanne “but that may make it difficult to restore understorey species in the long term because the treatments we might want to use to restore the understorey, such as repeated burning or even ploughing up a site to establish native grasses, are difficult if you have young trees planted.”
Suzanne says it is possible to restore understorey species in sites that are already wooded but options are more limited.
“It is something that is better thought about at an early stage,” she says. “One of the big problems with planting trees can be the invasion of weeds that you get when the country isn’t stocked. Making sure you get the understorey species (such as kangaroo grass) in first may be a practical answer, and may also be
better for natural tree regeneration. Simply fencing off a degraded system and letting it look after itself usually doesn’t work for the understorey.”
Suzanne says the key is a good, dense sward of the right native grasses that will suppress soil nitrate and control the weeds.
“To get there you need to first deal with the weeds, which you can do in a number of ways,” she says.
“One way that is particularly promising for controlling annual weeds [like Wild Oats and Patterson’s Curse] is to use sugar to temporarily reduce soil nitrate. This dramatically reduces growth of these nitrogen loving weeds, so you can get good establishment of native grasses. The native grasses then take over, and help to keep soil nitrate low. We suspect kangaroo grass is better than other native grasses for controlling soil nitrate in the longer term.”
The researchers have also found that burning in mid-spring can lead to a dramatic reduction in annual grass weeds by the next spring. Many annual grasses have short-lived soil seed banks, so preventing seeding through spring burning leaves few seeds for next year’s weed crop. However broad-leaf weeds can do very well after spring burning.
Suzanne and her colleagues have not focused on herbicides as a management tool for controlling weeds in their trials, because they aimed to address underlying processes that promote weed invasion. But it would be possible to incorporate agronomic techniques into the restoration “toolkit”. “What you could do is plough up a paddock, sow kangaroo grass as you would a crop, say in August, burn the annual weeds that have come up in mid October –it may be difficult to burn at that time of the year so you could kill of the weeds first with steam or a herbicide before burning- then use sugar for post-establishment weed control,” says Suzanne.
In the trials, the best establishment of kangaroo grass occurred when a burning treatment had been included. Kangaroo grass seed, like that of many native species, is stimulated to germinate by fire.
Suzanne says a lot more research is needed before firm recommendations can be made to landholders.
However a number of people are already experimenting with using sugar to control weeds with good results in the short term.
by Margrit Beemster
Sugar has the potential to control annual weeds according to recent research trials conducted by researchers from Charles Sturt University.
The researchers, ecologists Dr Suzanne Prober, Dr Ian Lunt and Dr Kevin Thiele, have applied sugar to trial plots for a project funded by the NSW Environmental Trust on how to restore understorey species in endangered Grassy White Box Woodlands.
Trials on a private property “Windermere”, and a travelling stock reserve “Green Gully” near Young in central NSW have provided dramatic results, with Paterson’s Curse and Wild Oats flourishing in untreated plots whilst plots treated with sugar had far fewer annual weeds.
The researchers have found that sugar provides a good, short-term non-chemical and ecologically friendly method of weed control.
“It appears sugar is a tool we can use to help change a system back to one dominated by native species rather than weeds,” says Dr Suzanne Prober who has been working to conserve and restore grassy white box woodlands for the past 15 years. Nearly all of the woodland belt, from southern Queensland to northeast Victoria is now used for agricultural purposes, principally wheat and sheep.
So why does the sugar work?
Because it is one of the fastest ways of reducing soil nitrate levels.
Dr Prober’s compared soil nutrients in undisturbed woodlands and disturbed, degraded sites. She found the most striking difference between the two was in nitrate levels, which were extremely low in undisturbed remnants and high in degraded remnants.
“It seems that many of our weed problems are due to high nutrient levels”, says Dr Prober. “There is an enormous amount of information on how to increase soil nitrogen to improve crop growth, but very little on doing the reverse. However there has been some research done overseas where sugar was used to tie up nitrogen levels for a short time.”
The researchers, who spread half a kilogram of refined white sugar to each square metre of soil every three months, found this inhibited weed growth of most annual weeds giving the native plants the opportunity to become well-established. However more research is required to work out the optimum rate of application.
“We realise that the sugar levels we used in our trials would not be economic to use over broad scales”, said Dr Prober, “but at the moment we don’t know if we would get similar results if we used less sugar or if we used cheaper alternatives such as molasses or sawdust”.
So how does sugar reduce soil nutrients?
“When sugar is spread on the soil, it feeds soil micro-organisms, which then absorb lots of soil nutrients as they grow,” explains Dr Ian Lunt from CSU’s Institute for Land, Water and Society.
“The micro-organisms then hold these nutrients so the weeds can’t gobble them up. In effect we are ‘starving’ the weed species that require lots of nutrients to grow.”
The lack of nutrients stopped the weeds from growing large, allowing the native plants, which can grow well in low nutrient levels, to grow bigger and faster.
The trial plots are now in their fourth year and the researchers believe that as the native grasses they have sown grow large enough, they will be able to lock-up the nutrients in their roots which will keep the weeds in check in the long run. Early results have indicated that nitrate levels are starting to drop in the plots with well established kangaroo grass.
“We see what we have done so far as only part of the picture,” says Dr Prober. “There are a number of directions we would like to go. One of our Honours students, Lisa Smallbone, is looking at whether sugar helps us to re-introduce native wildflowers into degraded sites. If the wildflowers establish well, we want to find out if they contribute to weed control and soil nitrogen cycling later on. Our long term goal is to get the native diversity back into the understorey by working out the best method to re-establish a native ecosystem that is self-sustaining and resistant to invasion by weed species.”
Using sugar as an organic weed control, to help to restore endangered woodlands and native grasslands, is an innovative alternative to using herbicides.
“Herbicides are difficult to use in many remnants because they kill the native plants you are trying to save as well as the weeds,” says Dr Lunt. “Sugar does not have this undesirable effect. Herbicides also don’t reduce the soil nitrate as sugar does, which is the underlying reason for the flourishing weeds – they control the symptoms, not the cause. Sugar may also be a useful way to control weeds that grow near other endangered native plants.”
While the researchers are primarily interested in using sugar as a tool to help restore the understorey species in grassy box woodlands, they are aware their research could be the basis for other more agriculturally driven research.
“Broad leaf weeds such as Patersons’ Curse are the bane of every farmer’s life. Once infestations get very bad, it gets very difficult to control them,” said Dr Lunt. “Sugar may help land managers to control broad-lead weeds and to re-introduce perennial grasses in many places across the region. In particular, it could be a really helpful tool in organic farming or in places where herbicides are difficult to apply.”
Conservation Management Networks
Dr Suzanne Prober’s passion to conserve Grassy Box Woodlands was the inspiration and driving force behind the establishment of the Grassy Box Woodlands Conservation Management Network in 1998.
The network, which now has 682 members including 355 private land managers, local governments and Rural Land Protection Boards, was the first in Australia. There are now seven such conservation networks helping to conserve fragmented ecosystems in NSW and Victoria. The Grassy Box Woodlands Conservation Management Network is now managed through the Department of Environment and Conservation (DEC) in NSW.
When Suzanne, as a researcher with CSIRO, first began looking for woodland remnants 15 years ago, she found that there were no large, undisturbed areas that could adequately represent the woodlands in a National Park.
“What we have instead are little bits and pieces, scattered across three states, and each bit is important for different reasons,” says Suzanne who spent a year searching for remnants on private and public land.
“There might be a travelling stock route that’s really important because of its big trees or a little cemetery that has got the best native understorey and is the only place where some native plants still grow.” One such cemetery is at Monteagle, in central NSW, where Suzanne is conducting the only long-term fire frequency experiment in the native grassland ecosystems in southern Australia.
The Network, now coordinated by Toni McLeish, has its own newsletter “Woodland Wanderings” and has a number of goals including protecting remnants and supporting best-practice management. Sites have been protected by various means including legal protection via covenants and listings on local environmental plans; purchase by the Australian Bush Heritage Fund; or as Suzanne says “some sites just have a really interested owner who wants to try and do the right thing.”
“We tried to create a network that brought together all these disparate sites into what we called a ‘conceptual reserve’ with many different tiers, but with a link between them all,” explains Suzanne.
“I still see it as early days and the concepts will evolve. Since we established the Network a lot of things have happened in the landscape, but at the time we felt we had to make something actually happen on the ground rather than just “monitoring the decline.
“Fundamentally, the conservation management network aims to help landholders and site managers, which is the most important step we can make. It provides great information to help us all to learn from everyone’s experiences, and it demonstrates to everyone how their individual actions are helping to save one of Australia’s most endangered ecosystems, grassy box woodlands.” - Margrit Beemster
Hints for Establishing Understorey
The research being carried out by Dr Suzanne Prober and her colleagues may well provide answers for land holders and managers who find the management of weeds a problem in tree plantations and sites that have been fenced off to allow for natural regeneration.
“What we tend to do these days is fence off an area and plant trees in it,” says Suzanne “but that may make it difficult to restore understorey species in the long term because the treatments we might want to use to restore the understorey, such as repeated burning or even ploughing up a site to establish native grasses, are difficult if you have young trees planted.”
Suzanne says it is possible to restore understorey species in sites that are already wooded but options are more limited.
“It is something that is better thought about at an early stage,” she says. “One of the big problems with planting trees can be the invasion of weeds that you get when the country isn’t stocked. Making sure you get the understorey species (such as kangaroo grass) in first may be a practical answer, and may also be
better for natural tree regeneration. Simply fencing off a degraded system and letting it look after itself usually doesn’t work for the understorey.”
Suzanne says the key is a good, dense sward of the right native grasses that will suppress soil nitrate and control the weeds.
“To get there you need to first deal with the weeds, which you can do in a number of ways,” she says.
“One way that is particularly promising for controlling annual weeds [like Wild Oats and Patterson’s Curse] is to use sugar to temporarily reduce soil nitrate. This dramatically reduces growth of these nitrogen loving weeds, so you can get good establishment of native grasses. The native grasses then take over, and help to keep soil nitrate low. We suspect kangaroo grass is better than other native grasses for controlling soil nitrate in the longer term.”
The researchers have also found that burning in mid-spring can lead to a dramatic reduction in annual grass weeds by the next spring. Many annual grasses have short-lived soil seed banks, so preventing seeding through spring burning leaves few seeds for next year’s weed crop. However broad-leaf weeds can do very well after spring burning.
Suzanne and her colleagues have not focused on herbicides as a management tool for controlling weeds in their trials, because they aimed to address underlying processes that promote weed invasion. But it would be possible to incorporate agronomic techniques into the restoration “toolkit”. “What you could do is plough up a paddock, sow kangaroo grass as you would a crop, say in August, burn the annual weeds that have come up in mid October –it may be difficult to burn at that time of the year so you could kill of the weeds first with steam or a herbicide before burning- then use sugar for post-establishment weed control,” says Suzanne.
In the trials, the best establishment of kangaroo grass occurred when a burning treatment had been included. Kangaroo grass seed, like that of many native species, is stimulated to germinate by fire.
Suzanne says a lot more research is needed before firm recommendations can be made to landholders.
However a number of people are already experimenting with using sugar to control weeds with good results in the short term.