Mycoherbicide for control of Giant Buttercup
A fungus that rots carrots in the fridge and causes lettuces to go brown in the garden is likely to become a useful weapon for farmers fighting to control a number serious pasture weeds a hit list that may include some of the common thistles and gorse.
This is a result of more than twelve years research into the naturally occurring organism Sclerotinia sclerotiorum by a team of AgResearch scientists at Lincoln.
Led by Dr Graeme Bourdt, scientist for AgResearch, the group has so far concentrated most of its effort on Giant Buttercup (Ranunculus acris), a very persistent weed that is costing farmers in excess of $100 million dollars every year.
An overgrown cousin of the better known creeping buttercup, Giant Buttercup is unpalatable to cattle and spreads rapidly to dominate pastures in favourable conditions. Much of Taranaki and parts of several other dairying regions including Takaka suffer heavy infestations that crowd out grasses and clovers and reduce milk yields. The loss to the New Zealand dairy industry in the 01/02 season was calculated at over $150 million and that figure is likely to be higher now.
Back in the 1950s this weed could be held at bay with phenoxy herbicides like MCPA and MCPB, but over the decades it developed resistance to them and, despite the advent of new synthetic chemicals, the problem has continued unabated.
Now, biological control with Sclerotinia shows promise. Graeme Bourdt says that trials in the Golden Bay region have achieved an impressive kill rate of 60% and better.
Under good conditions even surviving plants were restricted in growth so that overall reduction in the ground cover of Giant Buttercup was often over 70%. Results are rapid you can see plants dying off within a few days, he says.
Once Sclerotinia gets a hold, the effect on the host plant is devastating. The fungus produces an 'infection cushion' on leaf surfaces a mass of thread-like filaments or hyphae. Some of these soon penetrate the leaf cuticle and grow throughout the buttercup, breaking down cell walls and enabling the fungus to feed on the cell contents.
As the plant rots away and the fungus runs out of food, it produces seed-like resting bodies that fall onto the soil. The following spring these produce fruiting bodies and release spores that can infect remaining buttercup plants and seedlings.
Sclerotinia occurs naturally in pastures and cropping land where it causes sporadic disease outbreaks in susceptible weeds and crops, but to be successful as a mycoherbicide it needs to be concentrated and supplied with nutrients so that it establishes quickly on target plants, says Dr Bourdt.
Initially we developed a granular formulation designed to be applied with a standard fertiliser spreader. The best time to apply seems to be in spring when pastures are reasonably long and moist. The fungus grows on the leaf surface for a few hours using the food source that we supply in the formulation, then attacks the buttercup.
There still remain wide differences in success between farms and between treatments carried out within weeks of each other. Dr Bourdt believes that local environmental conditions are important too dry and the granules roll off the leaves; too wet and they are washed off. Temperature may also have an effect.
Extensive trials have been carried out to determine the reasons for the variation and the analyses are being done now. The range of kill varied from 20% to 80% with an average of over 50%. This is about the same range as with chemical herbicides because of the development of resistance in some plants.
The mycoherbicide approach has other important benefits:
Does not harm grass or clover species
Unlikely to harm nearby susceptible crops eg. rape
Resistance very unlikely to develop even with prolonged use
Meets market demands for reduced chemical use
Shows potential with other species, such as gorse, thistles and aquatic weeds
The company Encoate Ltd has been set up to commercialise biological technologies such as mycoherbicides.
Undoubtedly the technology we are developing now can be adapted to other species and other pathogens, says Dr Bourdt.
In time we could be looking at a suite of mycoherbicides formulated to control specific weeds in specific environments.
With consumers demanding low-chemical, ecologically sensitive production systems, mycoherbicides comprising naturally occurring plant pathogens will make it much easier to meet the demands of the worlds sensitive food markets.
Graham Ball, a Marlborough dairy farmer, has had giant buttercup on property since the early 60s. It was a time when the dairy industry was expanding and sheep numbers reducing, and since sheep do control the buttercup the lack of them contributed to the buttercup taking over.
When we first started spraying we got a about a 90% kill but now it only just keeps it under control and if you dont spray annually you find that the buttercup starts taking over again, says Graham.
MCPA and MCPB are widely used in the region, and he uses Preside herbicide.
He believes the mycoherbicide has good potential if it can be produced in a formulation that will adhere well to the plant. Use of it is likely to take a bit more planning and persistence than with chemical herbicides. It will be another tool in the toolbox for buttercup control.
Graham is adamant that funding of research into the control of buttercup must continue. With the spread of the dairy industry and the removal of sheep there is the chance that seed will find its way onto clean properties, and there is the potential for rapid spread. Farmers will have to be very vigilant to get rid of it before it gets established, and they will need all the tools they can get.
This is a result of more than twelve years research into the naturally occurring organism Sclerotinia sclerotiorum by a team of AgResearch scientists at Lincoln.
Led by Dr Graeme Bourdt, scientist for AgResearch, the group has so far concentrated most of its effort on Giant Buttercup (Ranunculus acris), a very persistent weed that is costing farmers in excess of $100 million dollars every year.
An overgrown cousin of the better known creeping buttercup, Giant Buttercup is unpalatable to cattle and spreads rapidly to dominate pastures in favourable conditions. Much of Taranaki and parts of several other dairying regions including Takaka suffer heavy infestations that crowd out grasses and clovers and reduce milk yields. The loss to the New Zealand dairy industry in the 01/02 season was calculated at over $150 million and that figure is likely to be higher now.
Back in the 1950s this weed could be held at bay with phenoxy herbicides like MCPA and MCPB, but over the decades it developed resistance to them and, despite the advent of new synthetic chemicals, the problem has continued unabated.
Now, biological control with Sclerotinia shows promise. Graeme Bourdt says that trials in the Golden Bay region have achieved an impressive kill rate of 60% and better.
Under good conditions even surviving plants were restricted in growth so that overall reduction in the ground cover of Giant Buttercup was often over 70%. Results are rapid you can see plants dying off within a few days, he says.
Once Sclerotinia gets a hold, the effect on the host plant is devastating. The fungus produces an 'infection cushion' on leaf surfaces a mass of thread-like filaments or hyphae. Some of these soon penetrate the leaf cuticle and grow throughout the buttercup, breaking down cell walls and enabling the fungus to feed on the cell contents.
As the plant rots away and the fungus runs out of food, it produces seed-like resting bodies that fall onto the soil. The following spring these produce fruiting bodies and release spores that can infect remaining buttercup plants and seedlings.
Sclerotinia occurs naturally in pastures and cropping land where it causes sporadic disease outbreaks in susceptible weeds and crops, but to be successful as a mycoherbicide it needs to be concentrated and supplied with nutrients so that it establishes quickly on target plants, says Dr Bourdt.
Initially we developed a granular formulation designed to be applied with a standard fertiliser spreader. The best time to apply seems to be in spring when pastures are reasonably long and moist. The fungus grows on the leaf surface for a few hours using the food source that we supply in the formulation, then attacks the buttercup.
There still remain wide differences in success between farms and between treatments carried out within weeks of each other. Dr Bourdt believes that local environmental conditions are important too dry and the granules roll off the leaves; too wet and they are washed off. Temperature may also have an effect.
Extensive trials have been carried out to determine the reasons for the variation and the analyses are being done now. The range of kill varied from 20% to 80% with an average of over 50%. This is about the same range as with chemical herbicides because of the development of resistance in some plants.
The mycoherbicide approach has other important benefits:
Does not harm grass or clover species
Unlikely to harm nearby susceptible crops eg. rape
Resistance very unlikely to develop even with prolonged use
Meets market demands for reduced chemical use
Shows potential with other species, such as gorse, thistles and aquatic weeds
The company Encoate Ltd has been set up to commercialise biological technologies such as mycoherbicides.
Undoubtedly the technology we are developing now can be adapted to other species and other pathogens, says Dr Bourdt.
In time we could be looking at a suite of mycoherbicides formulated to control specific weeds in specific environments.
With consumers demanding low-chemical, ecologically sensitive production systems, mycoherbicides comprising naturally occurring plant pathogens will make it much easier to meet the demands of the worlds sensitive food markets.
Graham Ball, a Marlborough dairy farmer, has had giant buttercup on property since the early 60s. It was a time when the dairy industry was expanding and sheep numbers reducing, and since sheep do control the buttercup the lack of them contributed to the buttercup taking over.
When we first started spraying we got a about a 90% kill but now it only just keeps it under control and if you dont spray annually you find that the buttercup starts taking over again, says Graham.
MCPA and MCPB are widely used in the region, and he uses Preside herbicide.
He believes the mycoherbicide has good potential if it can be produced in a formulation that will adhere well to the plant. Use of it is likely to take a bit more planning and persistence than with chemical herbicides. It will be another tool in the toolbox for buttercup control.
Graham is adamant that funding of research into the control of buttercup must continue. With the spread of the dairy industry and the removal of sheep there is the chance that seed will find its way onto clean properties, and there is the potential for rapid spread. Farmers will have to be very vigilant to get rid of it before it gets established, and they will need all the tools they can get.