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Study puts chaff residue to the test against pest pressure

A weather station installed near Cummins in South Australia. It measures precipitation, temperature, relative humidity and soil moisture in straw and control areas. Photo: Kym Perry

A STUDY is underway to determine if Harvested Weed Seed Control Systems (HWSCs), which create chaff residue, promote increased crop pest activity and associated crop damage in the growing region of the south.

The South Australian Research and Development Institute (SARDI) is leading research to study the effect of chaff residue on the diversity and abundance of invertebrate pests and their natural enemies.

The project was initiated following observations by grain farmers of increased pest pressure associated with straw residues.

HWSC systems in Australian cereal crops are playing an important role in weed management with the increase in herbicide resistant weeds.

The loss of effective herbicides for several major weed species has necessitated the development of management tactics that prevent weed seeds from entering the seed bank.

Chaff heaps, chaff tramlining and chaff coating are methods of the HWSC system which result in a concentrated distribution of the chaff component in the paddock, limiting weed survival.

However, some growers adopting these HWSC systems have observed increased pest pressure associated with chaff residue and they are particularly concerned about the potential risk of associated crop damage.

SARDI entomologist Kate Muirhead said the study is being conducted in 14 enclosures at various locations in the GRDC Southern Region, including Yorke Peninsula, Eyre Peninsula and north central South Africa, as well as western Victoria.

A pitfall trap in a control plot (sequins removed) in Jeparit, Victoria. Photo: Kate Muirhead

“The sites selected represent different areas of annual rainfall, crop rotations and invertebrate pressures,” Dr Muirhead said.

The trials are managed by Hart Field-Site Group and Nutrien Cummins Ag Services in South Africa and Birchip Cropping Group in Victoria.

Dr Muirhead said the study will address two key questions:

  • How does the presence of straw lines or tramlines affect species composition, density and distribution of harmful and beneficial invertebrates, and risk of plant damage, in cereal crops in the southern region?
  • How do microclimatic conditions in different chaff residues affect abundance patterns of invertebrate species?

“The invertebrate species of interest in the study are crop establishment pests that reside in the enclosures throughout the year – soil insects (earwigs, centipedes, slates) , molluscs (snails, slugs), mites, alfalfa flea and beetles/weevils.

“The main beneficial groups are predatory mites and beetles, ants, and recyclers of organic matter such as springtails, book lice and others.”

Two systems in the spotlight

The experiment will focus on two HWSC management systems – chaff tramlining and chaff coating.

The diversity of pests and beneficial invertebrates in the experimental plots will be assessed twice a year during the study – in the fall before sowing and shortly after crop emergence.

Dr Muirhead and his team recently removed the pitfall traps installed in the 14 paddocks included in the study.

“The contents will undergo diagnostic analysis over the next few weeks, and we will reinstall the pitfall traps once these enclosures have been seeded,” she says.

“A time-lapse video camera will also be installed on each of the seven farms after sowing to monitor crop sowing and directly identify the species causing the observed damage.”

The project will end in April 2024 and the research results will inform the need for specific crop pest management in HWSC systems and address potential barriers to their adoption by quantifying the risk to crops from invertebrate pests.

Source: GRDC