A project to determine optimum temperatures for killing weed seeds when burning narrow windrows in low-rainfall systems aims to provide farmers with more accurate data for the non-herbicide control strategy as resistance builds to herbicides.
The SAGIT-funded, 12-month trial, which started last year, will test temperature thresholds for killing seeds of common species, enabling landholders to “assess the value of narrow windrow and other burning strategies”.
Project supervisor, Naomi Scholz, from the South Australian Research and Development Institute (SARDI), the research division of Primary Industries and Regions SA (PIRSA), says the project fits with a wide range of integrated weed management trials for low-rainfall farming systems, including swathing and several trials for barely grass seed collection.
The two components of the project involve finding out what temperatures are achieved during paddock burns and the temperatures at which seeds of individual species are killed.
Ms Scholz said that if the project – which follows similar Western Australian research focusing on ryegrass and wild radish – could determine temperature thresholds for killing certain weed seeds, farmers would have more confidence when they chose the windrow burning option.
Temperatures during windrow and paddock burns at EP and Upper North farms were gauged using laser-type thermometer ‘guns’, with samples of crop residue levels collected.
This was carried out by SARDI staff and farming system group members during controlled burns.
Weed seed samples of barley grass, brome grass, wild oats, Indian hedge mustard, onion weed, Lincoln weed, statice, mallow, wild turnip and annual rye grass were collected last summer and autumn by Eyre Peninsula Agricultural Research Foundation, Upper North Farming Systems and Mallee Sustainable Farming groups.
Project collaborator, University of Adelaide researcher Ben Fleet, exposed these seeds to temperatures under controlled conditions in a muffle furnace (kiln) at Roseworthy, spanning the range of temperatures achieved when burning crop or pasture residues under field conditions. He is also conducting germination tests to gauge the effectiveness of killing the weed seeds.
Seeds were counted into batches of 100 and treated at different temperatures between 200oC and 450oC at times ranging from 20 seconds to a minute.
All seeds will be given the chance to germinate, and calculations of species that do worked out as a percentage to the control (untreated).
”It won’t be a perfect science, but it will give us a guide to see if we’re in the realm or not and it could be a pretty handy tool, adding to what growers already have,” he said. “It’s about managing expectations – and any weed control helps.”
Compilation of significant data on the mortality of the major weeds in SA low-rainfall systems during burning – and the impact on dormancy – could give farmers and advisers more precise knowledge about what they might actually achieve. If some, or all, the weeds prove vulnerable to temperatures typically applied in narrow windrows, there would also be incentives to modify harvesting approaches to improve the kill of those weed seeds.
“This is just one little piece of the jigsaw, along with other projects being developed, to give farmers options (to control weeds),” Ms Scholz said. If successful, it would also provide them with another tool for a non-herbicide weed control strategy.
The project report will be made available to farmers in February next year.