DPIRD entomologist Svetlana Micic is leading research, with GRDC investment, that is surveying invertebrate species and mice in unburnt chaff lines, tramlines and chaff dumps. Photo by DPIRD.
Grain growers are increasingly opting to use harvest weed seed control (HWSC) systems that collect chaff that is not burnt, but are they are capturing more than they bargained for?
This question is being addressed under a research project, initiated by the Grains Research and Development Corporation (GRDC), in which invertebrate species and mice are being surveyed in unburnt chaff lines, tramlines and chaff dumps.
The Department of Primary Industries and Regional Development (DPIRD) is conducting the GRDC-invested research to provide insights into how these newer HWSC systems influence populations of pests and beneficial species.
“Initial results suggest that chaff in paddocks in the southern areas of Western Australia is more likely to harbour invertebrates than chaff in the State’s central and northern grainbelt,” said DPIRD project lead Svetlana Micic, who discusses the research in a new GRDC podcast.
Entomologists, with the help of growers and grower groups, are looking at whether chaff lines and other harvest weed seed control are having an impact on invertebrate populations in a paddock.
Date: 27 Nov 2019
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“The research follows anecdotal reports that retaining chaff in paddocks has increased numbers of some invertebrate pests that could damage subsequent crops,” she said.
“We want to know if unburnt chaff increases invertebrate and mouse populations, so growers using non-burning HWSC chaff collection techniques know whether they are creating an environment that could foster more pests or beneficial insect populations.”
The newer HWSC techniques that do not involve burning include chaff lining. This involves using a simple chute to divert the weed seed-bearing chaff fraction (from the sieves) into a narrow chaff line, which is left to rot or mulch while the straw is chopped and spread.
Chaff tramlining is a similar concept to chaff lining, but the chaff is diverted through a chaff deck onto permanent wheel tracks in a controlled traffic farming system.
Chaff dumping involves collecting chaff using a cart towed behind the harvester. The chaff in the cart is then dumped, usually in piles in the paddock, and then either burnt, grazed or left to decompose.
The preliminary surveys, led by Ms Micic in 2019, suggest the geographical location of paddocks influences the abundance and composition of invertebrates associated with unburnt chaff. In addition, there is an indication that the type of chaff may also influence invertebrate abundance.
“Pitfall traps adjacent to chaff tram lines captured fewer invertebrates than traps next to chaff dumps or chaff lines,” she said.
Ms Micic said the project also assessed chewing or sucking damage to crops and confirmed plants grown close to chaff may sustain more invertebrate damage than plants located at least 20 metres from the chaff.
“However, we are yet to determine which pest species are responsible for the damage at the sites,” she said.
“Another interesting outcome was that the composition of species adjacent to chaff was different to that of species located 20 metres from the chaff – possibly suggesting some species may not be attracted to chaff.”
Ms Micic said the project tested the effectiveness of pitfall traps and chaff inspections as survey methods and had found that simple pitfall traps located up to 20 metres from chaff were sufficient to determine if a chaff system influenced invertebrates.
