Check what lies beneath the canola canopy
Author: Melissa Williams | Date: 13 Aug 2014
Researchers at the University of Western Australia (UWA) are confident earlier detection of some types of aphids is possible if you know where to look.
Late winter and spring has traditionally been the time to sample canola crops for cabbage and turnip aphids, which can cause widespread damage from feeding on leaves and shoot tips and sucking sap.
High numbers of aphids in crops heading into spring can result in wilting, flower abortion, reduced pod set, less pod fill and grain quality issues.
With funding from GRDC and the Department of Agriculture and Food, Western Australia (DAFWA), UWA PhD student Dusty Severtson is studying host plant selection and crop colonisation patterns by alate (winged) cabbage aphids in late season canola.
The aims of his project are to improve the accuracy and efficiency of aphid sampling and address two basic questions:
- When basing aphid sampling in canola on visual inspection, where in the paddock and crop canopy is it most likely an emerging infestation will be found?
- To what extent is it possible to automate sampling for aphids in canola based on the use of remote sensing technologies?
Last year, Dusty’s glasshouse and paddock-scale trial sites at UWA’s Shenton Park Field Station, York and New Norcia found:
- Cabbage aphids prefer to colonise the underside of lower leaves on canola plants, rather than the racemes (flowering spikes).
- These pests mostly aggregate along crop edges and 20-30 metres inwards – even where crops appear to be heavily infested.
- Non-crop areas within a paddock, such as contour banks and tree lines, may harbour aphids which spread on to nearby canola plants.
Targeted aphid sampling and treatment
A major implication from this research is that detection of cabbage aphids in canola crops may be possible weeks earlier than has been the traditional practice in WA.
This detection centres on checking the undersides of lower canola leaves during August, rather than inspecting flowering spikes later in spring.
Dusty’s 2013 research trials, conducted under the supervision of UWA Associate Professor in Applied Entomology Christian Nansen, showed aphids consistently colonised the lower portion of the canopy first – even when racemes were present – and were detectable on the underside of leaves weeks earlier than on racemes.
Dusty says it may take several weeks from when cabbage aphids first colonise a canola crop to when they become detectable on racemes – where the insects have traditionally been sampled from.
He says it was previously assumed that cabbage aphids flew directly onto racemes, but this does not seem to be the case.
He also found there was a significant ‘edge effect’ at last year’s York and New Norcia trial sites, where cabbage aphids in late August were most commonly found within 20-30m of the crop border and rarely detected further into the paddock.
Where infestations were found further into the crop, these typically centred on non-crop areas - such as tree lines, patches of natural vegetation, dams and contour banks.
An infestation detected more than 400m into the crop at the New Norcia site was linked to wild radish in a nearby tree line – highlighting the importance of weed control to reduce in-crop aphid sources.
Dusty produced edge ‘grids’ that showed aphid populations significantly declined after 10-20m into the crop at both trial sites, even though the paddock appeared to be heavily infested from the edge.
He says this means a border spray might be as effective as a full paddock spray to control cabbage aphids.
Other benefits from partially spraying a paddock include the retention of beneficial insects, which can prevent secondary flare-ups of aphids, and less risk of aphids developing resistance to insecticides.
Dusty says also sampling canola crops with a sweep net is important for monitoring diamondback moth and native budworm caterpillars that are starting to be seen in some WA grainbelt areas.
And sweeping is important for detecting beneficial insects, such as parasitoid wasps, ladybird beetles and hoverfly larvae that feed on aphids and help to keep pest populations low.
Future developments in insect detection
Data from Dusty’s project is being used in another GRDC-funded project that involves UWA entomology and geography scientists and students testing an unmanned aerial vehicle (UAV) to remotely detect and assess stressed crop plants.
This is possible because the UAV can fly at fast speeds and hover.
The aim is to fast-track identification of specific crop stressors, such as insects, nutrient deficiencies or frost and improve strategic integrated pest management (IPM) practices for WA growers.
In time, using UAVs and latest camera technologies could be a cost efficient way to:
- Detect patches of insects and pests in broadacre paddocks for strategic and targeted pesticide applications.
- Find nutrient deficient areas of paddocks for specific testing and treatment.
- Fast-track identification of frosted areas to make marketing decisions.
Reporting insect and pest incidence
Growers and advisors are encouraged to report incidences of crop pests and diseases, including cabbage aphids, via email to DAFWA’s PestFax service at: email@example.com
Caption: Researcher Dusty Severtson, of UWA and DAFWA, in a New Norcia paddock that was one of the 2013 sites for field trials researching the distribution of cabbage aphids. Photo supplied by UWA.
UWA and DAFWA
0422 157 769
Assoc Prof Christian Nansen
Dusty Severtson’s 2014 Crop Updates Paper: ‘Non-random distribution of cabbage aphids in canola’: www.giwa.org.au/2014-crop-updates
GRDC Crop Insects Ute Guide: www.grdc.com.au/Resources/Ute-Guides/Insects/Aphids-leafhoppers/West/Cabbage-Aphid
DAFWA PestFax email service: firstname.lastname@example.org
GRDC Project Code UWA00144, UWA00158, UWA00165