Your canola crop hasn’t outgrown the winter blues. It has moisture, plenty of applied nitrogen, sunshine, and warm weather. So why isn’t it thriving? It might be carrying Turnip Yellows Virus (TuYV).

It could be serious. Estimates of damage caused by TuYV infection range from 5-75% yield loss, which will hurt, especially in an expensive year.

What do we know, and what can we do?

Until recently, I had no first-hand experience with this problem, so much of the information below is compiled from other sources.

TuYV symptoms include stunted growth, red, yellow, or purple foliage, and stiff lower leaves (PestFacts South Eastern, 2017).

Figure 1. Confirmed infected canola.

Figure 2. Confirmed infected canola.

Figure 3. Very stunted and confirmed infected canola.

Figure 4. Confirmed infected canola.

 

This is the first year we’ve tested for TuYV in earnest, so we can’t determine how often we’ve had it in the past without knowing. I’ve submitted other samples to see if any healthy-looking crops are also infected with the virus. If so, not all the poor crop health may be due to the virus.

Reported yield losses from TuYV vary widely, which makes sense given that we’ve seen Green Peach Aphid (GPA) in canola plenty of times, but this is the first time TuYV has been a significant problem. The most recent edition of DPIRD PestFacts reports TuYV in canola at Allanooka, East Nabawa, and Nangetty. I’ve also had samples from Mingenew and Geraldton test positive. So, the issue is present, but the extent is unknown.

Formerly known as Beet Western Yellows Virus, it has occasionally caused significant yield loss in canola crops. The virus is mainly transmitted by the Green Peach Aphid (GPA). GPAs don’t inherently carry TuYV but can readily transmit the virus. During feeding, they can acquire the virus from an infected plant, carry it, and then transmit it to uninfected plants when they change hosts. This could mean that next year the risk of TuYV infection from GPA is much greater.

TuYV can be transmitted from a vectoring aphid to a plant quickly—within 15-30 minutes of the start of feeding (Stephanie Ann Veskoukis, 2023). This makes it difficult to prevent with insecticides—GPAs are generally resistant to common aphid anti-feeds (Alpha Cypermethrin, Gaucho, and Cruiser Opti seed treatments), and timing the sprays to kill them when they arrive but before they start feeding is challenging.

Table 1. GPA resistance status relative to common chemicals, with tradenames in Bold.

Yield losses from TuYV infection in WA field trials are estimated at 46% (Agriculture Victoria, 2022), but the more you read, the wider the range of expected yield loss becomes. If infection occurs before the rosette stage, yield losses tend to be more severe, while later infections may only reduce oil content by a few percentage points.

The seed dressing on store-bought hybrid canola seed (Gaucho, Cruiser Opti, etc.) should theoretically suppress GPA feeding, but the prevalence of TuYV this year means it’s clearly an imperfect strategy, especially with confirmed resistance to these insecticides.

The fact that this virus is present this year is remarkable for a few reasons.

We endured a hellish summer—scorching hot and bone dry, with even native trees and shrubs succumbing to the conditions. A green bridge would increase the incidence of GPA and, therefore, the risk of early TuYV transmission, and we certainly didn’t have that!

I scarcely noticed GPA in any canola crops except those that had some plants emerging early, though this wasn’t a perfect correlation.
We’ve had slow starts to canola before, including after kinder summers, with GPA present in roadside vegetation, but haven’t had to deal with TuYV.

This leads one to think that when canola emerges earlier and grows faster through winter, it may be able to outgrow the virus and limit yield losses.

As it stands, we seem to have defied expectations and ended up with TuYV in canola. PestFacts reported that GPA sampled around Irwin did not harbour TuYV, and traps set around Mingenew, Geraldton, and Nabawa did not detect GPA. See below.

Figure 5. Results of the GPA and TuYV monitoring sites, from 10/7/24. Source: (DPIRD PestFacts, 2024).

The early July ‘no-detection’ of TuYV in GPA makes it all the more remarkable that the virus has become evident and problematic.

Short Points

• The virus is not seed-borne, so it is unlikely to have arrived in the bought seed. This also means that keeping seed from infected canola this year won’t be catastrophic, but it’s hard to imagine it will be of great quality anyway.
• We have seen GPA plenty before but are seeing TuYV for the first time. Perhaps in good growing conditions, we can outgrow it?
• It’s not a new disease, but it’s the first time it has been a significant issue in the Geraldton port zone since at least 2016.
• The virus is carried by aphids. GPA seems to be by far the most effective vector of the disease, but cabbage and turnip aphids can also harbour it.
• Aphids don’t necessarily carry it but will transmit it from an infected plant to other plants they feed on.
• Yield losses due to the disease are 10% to 50%, maybe more, maybe less. This year it is difficult to separate canola looking sad for reasons of waterlogging and leaching from those of TuYV.
• Lupins are not likely to be an issue for TuYV. Although they are susceptible to infection and feeding by GPA, they rarely cause problems in lupins. Background alkaloid levels seem to do a good job of suppressing aphids in early lupin crops, and indeed in all lupin crops.
• Hosts of the GPA include radish, capeweed, volunteer canola, mallow, and turnip, and by extension, TuYV (Lilia Jenkins, 2024). Regardless, with aphids and TuYV present, green bridges will pose a higher risk moving forward. Pastures and volunteer canola should be controlled over summer to minimise the risk of re-infection next year.

 

Older screening work found some differences in resistance between varieties (Ben Congdon, 2019). Newer varieties may also exhibit this, but I can’t see evidence of screening work since 2018.

Where to Now?
There is no evidence of anything that can help the crop overcome the virus once it’s infected. Given the yield penalty is unknown and ranges from minimal to severe, it is hard to know which way to jump. At a guess, keeping the plant healthy seems the best bet. If the virus has been around for years without us noticing, the yield loss could be negligible. If it has only appeared this year and coincides with crops suffering from waterlogging and leaching, it’s difficult to say.

What would you do next year?

The short interval between aphids arriving, feeding, and transmitting the virus makes it impossible to control with sprays. Especially in what was a very busy period this year, it would not have been feasible to spray crops, especially when there was so little aphid pressure already. If nothing else, take advantage of the landscape-size screening trial we have. If you have more than one variety of canola and notice a difference in vigour or crop health between varieties, it may indicate a difference in innate resistance. Take notes and inform your agronomist. Testing is available, and at the very least, determining the size of the problem and any varietal differences will be useful.

Further, it seems reasonable that with plants confirmed as infected this year, there is a much higher risk for green bridges to harbour infection and readily transmit it to next year’s crops. Be vigilant about spraying out pastures, summer weeds, and anything that might harbour the disease into next year.

The resistance of GPA to insecticides makes control especially problematic. Only three specific insecticides are registered for control, and one is developing resistance, making it crucial to protect these. This means using them judiciously and paying attention to the small things that make GPA less of an issue. Principally, this involves IPM principles that encourage beneficial predator insects to help avoid GPA developing resistance to insecticides.

In the meantime, I will be testing more suspect crops for TuYV and trying to gather more information.

References
Agriculture Victoria. (2022, June 10). Turnip Yellows Virus. Retrieved from Agriculture Victoria: https://agriculture.vic.gov.au/biosecurity/plant-diseases/grain-pulses-and-cereal-diseases/turnip-yellows-virus

Congdon, B. (2019, February). Turnip Yellows Virus Epidemics in 2018. Perth: GRDC Research Updates.

DPIRD PestFacts. (2024, July 19). PestFacts Issue 9. Retrieved from DPIRD: https://www.agric.wa.gov.au/newsletters/pestfacts-wa/pestfacts-wa-issue-9-19-july-2024?page=0%2C3

Jenkins, L., Umina, P., & Ward, S. (2024, June 3). Concerns of the Turnip Yellows Virus in Canola. Retrieved from Cesar: https://cesaraustralia.com/pestfacts/concerns-of-turnip-yellows-virus-in-2024/

PestFacts South Eastern. (2017, August 17). Turnip Yellows Virus present in some canola paddocks. Retrieved from Cesar: https://cesaraustralia.com/pestfacts/turnip-yellows-virus-present-in-some-canola-paddocks/

Veskoukis, S. A., & Babinou, M. (2023, August 31). Reports of Green peach aphid a warning to look out for Turnip yellows virus. Retrieved from Cesar: https://cesaraustralia.com/pestfacts/green-peach-aphid-and-turnip-yellows-virus/