Canola farmers in South Australia are facing a formidable challenge as the Turnip Yellow Virus (TuYV) spreads across the state, threatening their crops. This insidious virus, transmitted by the Green Peach Aphid, has the potential to decimate entire fields, leaving behind a trail of yellowing and purpling leaves. The severity of the outbreak is alarming, with reports of near-total infection rates in affected paddocks. Dr. Nicole Thompson, a SARDI expert, highlights the importance of early detection and swift action. She recalls a case in the Padthaway/Bordertown area where a forage canola crop, initially showing symptoms of aphids, later revealed a staggering 100% TuYV infection within two weeks.
The virus's insidious nature lies in its ability to remain asymptomatic in some plants, making diagnosis challenging in the field. Dr. Thompson emphasizes the need for thorough inspections and early decisions regarding spray applications. The Green Peach Aphid, the vector of TuYV, thrives in 'green bridges' such as perennial weeds, forage brassica, volunteer canola, and new canola crops. Once infected, these plants become carriers, and the aphids feeding on them further spread the disease.
Dr. Maarten van Helden, another expert on the GRDC-run disease management webinar, underscores the urgency of the situation. He notes that while aphids typically attack in small numbers later in the season, this year's outbreak has been unprecedented, with populations booming. The use of pesticides like Versys and MainMan has shown some resistance, but the timing of their application is critical for effective control. The wet and cold weather, while challenging, also presents an opportunity for farmers to remain vigilant and take proactive measures.
Another concern is Sclerotinia stem rot, a disease affecting canola crops in Victoria and New South Wales. Dr. Kurt Lindbeck, a pulse and oilseed pathologist, advises against premature use of fungicides. He emphasizes that the optimal timing for these products is during the 20-30% flowering stage, when the crop has around 15-20 open flowers off the main stem. This stage, marked by a noticeable yellow hue across the paddock, triggers significant shedding or senescence of petals, which can lead to stem infections. Good coverage and penetration with a ground rig at this growth stage are crucial for effective control.
As the agricultural season progresses, farmers must remain vigilant and proactive in their disease management strategies. The challenges posed by TuYV and Sclerotinia stem rot demand careful monitoring, early detection, and timely interventions to safeguard canola crops and ensure a successful harvest.
