THE CLIMATE KELPIE BLOG: New forecasting tools aid Red Witchweed cull

Posted by BCG on 6th April 2021

Queensland Government Biosecurity Officer Tom Bowditch is looking forward to the public release of new Bureau of Meteorology climate forecasting tools that will fill a need for better medium-term forecasts.

Red Witchweed is the target of an ambitious $5.8 million eradication program.

Tasked with coordinating an ambitious $5.8 million eradication program for Red Witchweed in the Mackay region, Tom credits his early access to the experimental forecasts with improving the effectiveness of the program, as well as making his scheduling of activities and staffing a lot easier.

Three new tools, which have been extensively tested by agricultural industry representatives from across Australia, will be released during 2021. The tools were developed as part of the Commonwealth Government’s Rural R&D for Profit ‘Forewarned is Forearmed’ (FWFA) project.

Million-dollar program

Red witchweed (RWW) is a parasitic plant that attaches to the roots of a host, which include commercially important grasses and summer cereals including sorghum, corn, rice and sugarcane. Seeds can remain viable in the soil for up to 15 years.

The weed is estimated to cost African farmers $7 billion in lost production per year. The United States has spent more than $250 million trying to eradicate it – to achieve eradication the plant must not be allowed to set seed.

New rain forecasts are useful for forward planning for staffing and equipment, helping to better manage logistics and the health and safety of staff. Project staff visit properties every 8-10 days and walk an average of 385 km in that time.

The program Tom is overseeing, which includes eight sugarcane and cattle properties, involves scouting for weeds, planting of false host and catch crops, application of weed control chemicals and soil fumigants, and earthworks to contain soil and weed seeds and prevent erosion.

Similar to the US experience with RWW, the reality of eradicating RWW is time consuming, labour intensive and expensive – chemical applications alone across the 90-hectare treatment area cost between $6,000 and $11,000. As well as being costly, herbicide applications need to be timed so that they are not washed away. Peak activities occur during the summer growing season when the region’s rainfall averages around 1,600mm from December to March. Understanding when rain is likely to fall and how much makes a big difference to program activities. 

In the past Tom relied on the standard one-week forecasts from the Bureau of Meteorology and MetEye. He also uses as it good for visualising rain, particularly for cyclonic lows. But the experimental forecasts coming from FWFA have given him the ability to view medium-term weekly or monthly forecasts (Figure 1).

“These have been invaluable for planning activities and staffing” said Tom.

Figure 1: The experimental forecast shows that February rainfall is expected to be much lower than the normal making it an ideal time to do groundwork. While the wide range on the March forecast indicates potential storms that can lead to very wet conditions means the teams need to be prepared for days of inactivity, followed by a heavy demand for scouting. Source: Bureau of Meteorology.

Anyone who grows a crop watches the weather closely to select the best time to apply pre-emergent herbicides and plant a crop so that it will flourish. But for Tom, any crop failure also means he has also missed a vital opportunity to control RWW.

“To ensure we get the most effective control of RWW we want to make sure our pre-emergent herbicides are applied just ahead of rain so that they work to control weeds that can act as alternative hosts for RWW. But we don’t want too much rain to wash them away either. For the same reason we want to sow our crops into the ideal moisture situation so that they flourish and generate successful germination of RWW.”

False-host crops such as sorghum are planted because the roots stimulate RWW germination, but attachment and subsequent growth are not supported so the seedling dies (suicide germination). The program also uses corn catch crops because they allow the RWW to grow and flower enabling intensive surveillance and treatment.

The program stimulates RWW germination using sorghum as a false host interspersed with a corn catch crop.

Rainfall forecasts are useful for forward planning for staffing and equipment, helping to better manage logistics and the health and safety of project staff.

“Our surveillance teams visit properties every 8-10 days and each round involves an average of 385 km of walking across some pretty steep land each day. In hot and humid conditions and wearing protective clothing they are pretty vulnerable to heat stress. The heatwave probability forecast allows me to plan ahead for periods of high risk and plan shorter shifts or roster on additional staff (Figure 2).”

The heatwave probability forecast enabled better forward planning for staffing during periods of high risk of heat stress.

Tom couldn’t be happier with the new forecasts.

“These forecasts have made my life much easier,” he said. “They are so much more informative than the old week-ahead forecasts. I can plan activities and staffing with more confidence than in the past. As we get closer to the date the forecasts become more accurate and I might need to refine my program, but these forecasts mean I have a much better feel about where we are headed.”

More information

Tom Bowditch, 0427 502 455,

Queensland Department of Agriculture and Fisheries Surveillance program for red witchweed

The Forewarned is Forearmed project is supported by funding from the Australian Government Department of Agriculture and Water Resources as part of its Rural R&D for Profit program. Project research partners: Bureau of Meteorology, South Australian Research and Development Institute, University of Melbourne, University of Southern Queensland, Birchip Cropping Group, Agriculture Victoria, Monash University and Queensland Department of Agriculture and Fisheries. Rural R&D Corporation partners: Meat & Livestock Australia, Dairy Australia, Wine Australia, Sugar Research Australia, Grains Research & Development Corporation, Agrifutures Australia, Cotton Research & Development Corporation and Australian Pork.

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