TuYV infection prior to stem elongation can cause up to 50% yield losses. For every one per cent increase in the level of TuYV in a canola crop there can be a 6-12 kg/ha decline in yield resulting from formation of fewer branches, pods and seeds. In addition to yield losses, TuYV infection diminishes seed quality by decreasing oil content and increasing erucic acid and glucosinolate levels. If the crop is infected after stem elongation, yield and quality losses are likely minimal.
Turnip yellows virus in canola: diagnosis and management
Turnip yellows virus (TuYV; formerly beet western yellows virus) is an aphid-borne virus that causes yield and quality losses in canola. It can also infect and impact other crop and pasture species including mustard, chickpea, lupin, lentil, faba bean, field pea, lucerne, medic and subterranean clover.
What to look for
- Symptoms can be inconsistent for TuYV and ‘symptomless’ infection may occur that still causes losses via reductions in branch and pod numbers, and seeds per pod.
- Under certain conditions, discoloured and stunted plants that occur in patches, in thinner crop areas or the edge of the paddock, and gradually spread.
Paddock
- First signs are red, yellow or purple colours at the ends or edges of older leaves, then yellowing in the middle of the leaf.
- Colours are more intense between leaf veins and on the upper side of the leaf.
- Petioles and leaf veins are green or pale.
- Discoloured leaves become thickened and may cup inwards.
- Infected plants are often stunted and pale, and produce fewer flowers, branches and pods.
- Late infected plants show leaf symptoms but are not stunted and have lower yield loss.
Plant
What else could it be
| Condition | Similarities | Differences |
|---|---|---|
| Diagnosing nitrogen deficiency in canola | Purple red colours spreading down from the ends of oldest leaves | However nitrogen deficient plants are smaller and thinner rather than stunted. Paddock distribution varies according to soil type rather than in patches or edges. |
| Diagnosing Group A herbicide damage in canola | Reddish mottling of older leaves | However herbicide damage causes discolouration and distortion of emerging leaves, and multiple growing points |
| Diagnosing glyphosate damage in canola | Reddish mottling of older leaves | However herbicide damage causes discolouration and distortion of emerging leaves, and multiple growing points |
Where did it come from?
Green bridge
Insect vector
- TuYV is regularly found in high and medium rainfall grainbelt zones but can also occur in low rainfall zones.
- Autumn is the most critical infection period, so the earliest-sown crops are most vulnerable when conditions for autumn aphid activity is conducive.
- It is not seed-borne, but survives in weeds or volunteer canola host plants outside the growing season and is spread from these infected plants into crops by aphids which act as vectors for virus transmission.
- The main source of TuYV for canola crops is infected wild radish weeds growing along fence lines and road verges or volunteer canola. Other weed hosts include wild melon, fleabane, stinkweed, soursob, marshmallow and blackberry nightshade. It also persists year-round in infected lucerne pastures and some native legume species.
- It also infects other crop and pasture species including mustard, chickpea, lupin, lentil, faba bean, field pea, lucerne, medic and subterranean clover.
- Green peach aphid is the principle vector for early, damaging spread and is highly efficient (i.e. 1 aphid can be enough to transmit TuYV to a canola plant).
- TuYV is transmitted persistently. When an aphid feeds on an infected plant it acquires the virus and is able to transmit the virus for the remainder of its life.
- When the infective aphid feeds on the phloem of a healthy plant it transmits the virus.
Management strategies
Stubble management
- Control broadleaf weeds (especially over summer) as they act as reservoirs for the viruses
- Retain stubble at sowing to cover the ground, this reduces the ability of aphids to land on young canola plants thereby reducing virus spread.
- Manipulate sowing dates. Delay sowing to avoid exposure of young canola seedlings to peak aphid flights in autumn.
- Sow at high seeding rates. High plant density helps diminish the rate of virus spread and speeds up canopy closure resulting in lower aphid landing rates.
- Use neonicotinoid seed treatment. When applied effectively they can provide early green peach aphid control during the vulnerable seedling growth stage.
- Consultants can deploy sticky traps to the fenceline during the early part of the growing season and send them to DPIRD Diagnostic Laboratory services (DDLS) for early detection of virus-carrying aphids in the environment (refer to DDLS webpage).
- Application of insecticides such as sulfoxaflor (Transform®) during the rosette phase to eliminate initial green peach aphid infestation, prevent widespread colonisation of the crop and reduce incidence of TuYV infection.
- IMPORTANT: Pirimicarb, organophosphate and synthetic pyrethroid insecticides are likely ineffective against green peach aphids because of widespread resistance.
- Generally, it is too late to intervene once symptoms have been observed and diagnosed as TuYV infection and aphids have spread through the majority of the crop. Insecticide application at this point is likely to be ineffective.
See also
Where to go for expert help
Page last updated: Monday, 15 March 2021 - 2:52pm