Dairy farmers have been handed two new hi-tech tools in the fight against the invasive giant buttercup, which is estimated to cost the industry about $200 million a year in lost milksolids production.
The buttercup is a weed with potential to make a serious dent in farm profits.
For farmers with 12% of the ground cover being in giant buttercups, it could reduce their farm’s profit by $1,040/ha. Researchers have developed a new tool that could deliver considerable productivity and economic gains.
A native of Europe, the giant buttercup successfully established itself in New Zealand at the beginning of pastoral farming and is now widespread on dairy farms in South Auckland, Hawke’s Bay, Southland, Taranaki, Wairarapa, West Coast and Tasman District.
The plant is particularly aggravating in Golden Bay, where AgResearch principal scientist Dr Graeme Bourdôt and colleagues have worked closely with farmers to develop the two tools as the components of a science-based decision support system. The system enables better informed decisions on controlling the weed with herbicides and managing herbicide resistance.
Downloaded onto a smartphone, the first of the two tools, the Grassland Cover Estimator (GCE) app, enables a farmer to figure out how much giant buttercup there is in a paddock.
“To determine if a giant buttercup infestation is worthwhile controlling, the farmer must first know how much of his paddock is covered by the buttercup. Is there enough to make it worthwhile controlling?” Bourdôt asks.
“To estimate the percentage of a paddock that is covered by the weed, the GCE app uses a method plant ecologists have used for years called point analysis. The app works by the user walking across a paddock and observing whether the weed is present or absent at the tip of their boot. The observations are recorded as present or absent by swiping one way or another, and the app uses these observations to calculate the percentage of the paddock covered by the weed.”
He describes it as a simple generic tool that is much better than guesswork for estimating the coverage of a plant in a pasture. While a farmer could stand on a fence post on the corner of the paddock and estimate buttercup cover, he would likely not be quite wrong.
“Unsurprisingly, to get a good estimate of the cover of the weed in a paddock, you need to make observations over a good proportion of the paddock. The advice is to cover as much of the paddock as possible. Every time you swipe the app as present or absent it does a running calculation of the percent cover, and you can see that as you’re walking,” he says.
The app also stores all observations and their geographic coordinates and this data can be exported from the phone to a PC for more detailed analysis and mapping if required.
Once the percentage cover has been established, the next step is to go to the second tool, the Giant Buttercup Decision Support Tool web app for a four-step process.
First the percentage of buttercup is inputted, followed by the second step of inserting various values related to productivity of the paddock (dry matter grown and eaten, pasture conversion rate, pasture utilisation). At this step, the milksolids payout price expected over the three years following the intended herbicide control programme is also inserted.
The third step offers a menu of herbicide treatment options including all 49 herbicide products currently on the market in NZ with a label claim for use against giant buttercup in pasture. Depending on which options are chosen, the app shows the current price of the products in dollars per hectare and the cost of application. The user can go ahead with these default values or replace them with other values. The final step shows the range in net benefit (in $/ha) that can be expected for each of the herbicide products that have been selected for comparison.
“Based on all the information you’ve put in, it works out how many kilograms of extra milksolids you could expect from the paddock if you control the buttercup with a particular herbicide,” he says.
“In calculating the net benefit for a particular proposed herbicide treatment, the app uses the cost of N fertiliser to account for the loss in fixed N resulting from the herbicide’s damage to clovers. Some herbicides can bowl out the clovers for a long time. Others have less effect, and some have no effect.”
Bourdôt says that underpinning the Giant Buttercup Decision Support (DS) Tool is a unique peer-reviewed and published data set from a three-year scientific experiment in 18 different dairy pastures in Golden Bay. The experiment compared all herbicide active ingredients currently on the NZ market for their effect on giant buttercup and on other pasture plants including the N-fixing clovers. It showed that the herbicides differ substantially in their effect on the weed and damage to clovers. These differences, along with variability in efficacy within each of the herbicides, are accounted for in the DS Tool, which calculates the expected range in net benefit for each herbicide in a selected comparison.
In the same experiment, other control methods were also investigated. One was to use a common fungus, Sclerotinia sclerotiorum that kills the giant buttercup in dairy pastures, turning the plants into a slimy, rotting mess.
Another method compared was to mow the pasture before grazing. Mowing neutralises the toxicity in the buttercup – its scientific name is Ranunculus acris, referring to the acrid tasting chemical in the plant which can become toxic and cause blistering of the lips and tongue, intestinal disorders, and potentially fatal ventricular fibrillation and respiratory failure.
“When you mow, the bitter chemical comes out of the mown giant buttercup foliage as a gas. The wilted foliage is no longer bitter or toxic and is readily eaten without harm to the cow,” Bourdôt says.
Because the giant buttercup has evolved resistance to some herbicides, pre-graze mowing is potentially an effective alternative option, even if it is more labour intensive. Mowing is currently not included as an option in the DS Tool.
The AgResearch study has been funded through the Sustainable Farming Fund, with support from the Ministry for Primary Industries, DairyNZ, and Ravensdown.
