Canola growers across Australia are facing a mounting challenge as they battle the insidious turnip yellows virus (TuYV) and its vector, the green peach aphid. This disease, once known as beet western yellows virus, is now a significant threat to canola crops, causing substantial yield losses and posing a complex management problem. The situation is particularly dire as recent research indicates that neonicotinoid seed treatments, once relied upon for protection, are no longer effective against the green peach aphid and the subsequent TuYV infection.
The conditions for the aphid's proliferation are favorable with warmer temperatures and recent rainfall. This makes monitoring and early intervention crucial. TuYV infections can be highly variable and often go unnoticed until it's too late, as symptoms may appear weeks or even months after the virus has been transmitted. This delay in symptom manifestation further complicates management efforts.
Dr. Ben Congdon, a senior research scientist at the Department of Primary Industries and Regional Development (DPIRD), emphasizes the importance of vigilant monitoring. He notes that foliar symptoms, such as leaf purpling or reddening at the margins of lower leaves, can be mild or completely absent, making it challenging to distinguish from nutrient deficiencies or environmental stresses. Therefore, he recommends aphid monitoring and virus testing as essential tools for informed spray management decisions.
The impact of TuYV on canola crops can be devastating. Infections can lead to yield losses of 10 to 20 percent, sometimes without any obvious symptoms, and in severe cases, losses can reach up to 50 percent. The timing of infection is critical; the greatest damage occurs when plants are infected during early development, from emergence to the seven-leaf stage. The severity of yield impact is directly related to the percentage of the crop infected and the speed of the virus's spread.
To combat this issue, DPIRD has contributed to a new fact sheet, 'Manage Turnip Yellows Virus in Canola,' which provides valuable information for optimizing crop potential. The fact sheet includes a comprehensive table on monitoring green peach aphids and guidelines for targeted insecticide applications. However, Dr. Congdon stresses the importance of careful monitoring and targeted insecticide use, warning against pre-emptive spraying, which is unlikely to provide effective control.
The situation is further complicated by the widespread use of neonicotinoid-based seed treatments, which have failed to adequately control the green peach aphid. This has led to an increase in TuYV infections across Australia, making it a growing problem for canola growers. As the growing season progresses, DPIRD's monitoring in the Northam, Geraldton, Albany, and Esperance areas will provide crucial insights into TuYV risk, and growers are encouraged to share paddock intelligence and report aphid observations to help manage this significant disease threat.
