Northern harvest weed-seed trials

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Photo of Annie ven der Meulen

Queensland DAF research scientist Annie van der Meulen inspects wild oats, which have been planted amid wheat plants in a trial at the Leslie Research Centre, Toowoomba, to supplement field trials on harvest weed seeds.

PHOTO: Elizabeth Wells

An initial survey into weed-seed retention at harvest (see Table 1) has shed new light on the nature of some of the most persistent species. The preliminary study has already dispelled the prior belief that black oats shed all seed prior to crop harvest.

Instead, Queensland Department of Agriculture and Fisheries (DAF) researcher Dr Michael Widderick says if black oats emerge after cereals they can, in different seasons, be less likely to shatter prior to harvest and therefore be picked up with the crop.

The results have encouraged researchers to start evaluating non-chemical harvest weed-seed-control for northern region growers.

Methods being evaluated include the Integrated Harrington Seed Destructor (iHSD) now being commercialised (see Seed destructor a model of R&D teamwork), which uses mills mounted within the harvester to process the exiting chaff containing weed seeds. Other tactics being tested include chaff tramlining, where chaff is concentrated on dedicated wheel tracks, along with narrow windrow burning and chaff carts.

Dr Widderick says it is important for northern growers to have management methods other than spraying up their sleeves to control weeds such as black oats, and to minimise the impact of herbicide resistance.

“Wild oats have already been identified as having resistance to Group A herbicides and some Group B and Group Z herbicides in the northern region. Additionally, other common weeds including fleabane, sowthistle and barnyard grass are now also frequently evolving resistance to glyphosate and other herbicides.”

A survey funded by the Rural Industries Research and Development Corporation (RIRDC) and conducted by Queensland DAF and the University of Queensland assessed weed distribution, density and seed production at harvest time in wheat, chickpea and sorghum crops across 1400 transects in 70 paddocks.

“When seed was retained on the weeds, most was at heights suitable for potential management with harvest weed-seed control,” Dr Widderick says.

Table 1 Survey of weed-seed retention.
Region and crop
Number of paddocks surveyed
Number of weed species present at harvest
Number of weed species retaining seed at harvest
 Central Highlands, Queensland
 Chickpeas 5 8 6
 Wheat 5 5 4
 Sorghum 10 12 11
 Darling Downs, Queensland
Chickpeas 5 11 7
Wheat 5 12 10
Sorghum 10 15 11
 South-West Downs, Queensland
Chickpeas 5 15 11
Wheat 5 8 3
 Sorghum 10 25 19
 Liverpool Plains, NSW
 Chickpeas 5 22 16
 Wheat 5 18 12
 Sorghum

SOURCE: Queensland DAF

GRDC investigation

A GRDC-funded project is now evaluating the potential role of harvest weed-seed control in the northern region. Development of the research is being overseen by Dr Michael Walsh, recently appointed as director of weed research at the University of Sydney.

Dr Walsh’s experience in helping develop systems to combat widespread herbicide resistance in Western Australia, including the iHSD and its predecessor the tow-behind Harrington Seed Destructor, is guiding the direction of research in the northern region.

Results from GRDC-supported on-farm trials by DAF research scientist Dr Annie van der Meulen have started to shed some light on the importance of harvest weed-seed control.

In a series of field experiments, harvest weed-seed control methods were applied in the 2015 winter-crop harvest, and 2016 data collection has started with emergence counts of target weeds on participating properties at North Star, Mungindi, Westmar, Talwood and Goondiwindi. 

Dr Widderick and Dr van der Meulen say that looking at harvest weed-seed control has not come a moment too soon in the northern region. “It can take herbicide resistance up to 10 to 15 years to rear its ugly head, so if we look at herbicide use patterns in the northern region coupled with the increasing incidence of herbicide resistance, now is the time we need to be ready with strategies to keep us one step ahead,” Dr van der Meulen says.

Researchers do not see harvest weed-seed control as the standalone cure or preventive measure for herbicide resistance, but see it a useful practice to supplement other weed-management tactics including single or double-knock spraying, crop rotations and discretionary use of tillage.

Dr Widderick says harvest weed-seed control looks to have great potential as an added tactic in integrated weed management, but how it is used depends on many factors, including climatic conditions experienced in each season as in-crop rain and temperatures will determine the time of weed emergence and subsequent seed retention at harvest.

“No one approach is going to provide 100 per cent control all of the time, but harvest weed-seed control might lift the efficacy of your weed management, which includes herbicide applications, from 80 per cent to 95 per cent,” Dr Widderick says.

The northern region project evaluating harvest weed-seed control runs until June 2018. 

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GRDC Project Code US00084, UWA00171

Region North, South, West