Check emerging canola crops for aphids that may be carrying turnip yellows virus
- Mount Barker
A small number of turnip yellows virus (TuYV) carrying aphids have been detected at; Cranbrook, Mount Barker, Borden, Ongerup, Woogenellup and Kalgan. These aphids were caught by yellow sticky traps deployed by the diamondback moth (DBM) surveillance team from mid-March to mid-April and these are a part of a DPIRD Boosting Grains Science Partnership project.
Plant virologist Benjamin Congdon (DPIRD) also reports finding cabbage and green peach aphid (GPA) in established wild radish on roadsides in the Albany port zone and both of these species can spread TuYV.
The presence of volunteer canola and cruciferous weeds (particularly wild radish) in the grainbelt can give aphids a chance to build-up which can increase the risk of early incursion of TuYV if winged aphids transmit virus from infected weeds to vulnerable germinating canola crops.
Growers in the Albany port zone are urged to monitor their germinating canola for aphids and signs of symptomatic plants.
In the Northam area, very low numbers of winged GPA have been caught on sticky traps. There is established patches of wild radish in this region so there is potential for green peach aphid numbers to increase over the coming months and pose a risk to emerged canola crops.
What is turnip yellows virus?
TuYV, formerly known as beet western yellows virus, is an obligate plant parasite transmitted by several aphid species that colonise canola including its principle vector, the green peach aphid (Myzus persicae) and the minor vector, the cabbage aphid.
It causes yield and quality losses in canola crops. It also infects other crop and pasture species including mustard, chickpea, faba bean, field pea, lucerne, medic and subterranean clover.
Timing of infection is key with heavier losses more likely if infection occurs during the rosette phase of canola up until stem elongation (GS30).
TuYV systemically infects plants and cannot be sprayed-out post-infection like a fungal disease. Therefore, control of the virus needs to be focussed on prevention rather than cure.
Diagnosing and preventing turnip yellows virus
Signs of TuYV infection in the paddock include discoloured and stunted plants that occur in patches, in thinner crop areas or the edge of the paddock, and gradually spread.
TuYV infection causes reddening, purpling or yellowing of the lower leaves of canola plants. Plants infected early (well before flowering) are often pale and stunted and these plants produce few flowers or seeds. Symptoms are milder and stunting is lacking with late infection. Leaf symptom type and severity differ depending on plant age at infection, environmental conditions and the canola variety involved. Symptoms of TuYV in canola can be confused with those caused by nutrient deficiencies, waterlogging or other plant stresses that cause yellowing, reddening or purpling of lower leaves.
TuYV spread can be controlled by applying neonicotinoid seed dressings.
Foliar sprays can also be applied to reduce infected aphid numbers but GPA has evolved resistance to many insecticide chemicals. Effective chemicals currently available in Australia for control of GPA are alarmingly limited. Overreliance and misuse of one of the remaining insecticides, sulfoxaflor (Transform®), could be leading to reduced sensitivity in some Australian GPA populations. For more information see GRDC’s Aphid and insecticide resistance management in grain crops.
For more information on this work refer to DPIRD’s Turnip yellows virus early warning system page.
For insecticide recommendations refer to DPIRD’s 2021 autumn winter insecticide guide.
Other management practices include; sowing into stubble and delayed sowing to avoid peak autumn aphid flights.
If you see aphids are colonising green bridge hosts, or you have symptomatic looking plants that you are concerned about, they can be tested for the presence of TuYV through the Department’s Diagnostic Laboratory Services – Pathology Services.
For more information refer to DPIRD’s Turnip yellows virus in canola: diagnosis and management and Turnip yellows virus early warning system pages.
For further information contact Benjamin Congdon, Research Officer, South Perth on +61 (0)8 9368 3499.
Article authors: Cindy Webster (DPIRD Narrogin) and Benjamin Congdon (DPIRD South Perth).