Twenty years ago, Fusarium Head Blight (FHB) infamously made headlines in New South Wales when the disease slashed durum wheat yields by up to 100 per cent across the Liverpool Plains region.
Economic losses were extensive, prompting industry to undertake a detailed evaluation of the agronomic and climatic factors that contributed to the devastating outbreak.
Since then, the Grains Research and Development Corporation (GRDC) and its research partners have invested in research and extension efforts to better manage the disease and minimise the risk of history repeating itself as soon as weather conditions are conducive – that is, wet and humid during flowering and/or grain fill.
To avert a similar outbreak, experts say it’s important for industry to recognise the key FHB risk factors and implement preventative agronomic strategies where possible, particularly if the cropping program includes cereal crops and maize within the rotation.
With the rapid expansion of these crops in some irrigation areas of southern NSW, growers are being urged to implement an integrated FHB management program that includes the use of non-grass crops in the rotation as a disease break, and testing of at-risk paddocks and potentially planting seed following seasons conducive to FHB development.
NSW Department of Primary Industries (DPI) senior plant pathologist Steven Simpfendorfer said rotation selection was one of the most important management tools in minimising FHB infection-risk and recommended avoiding durum-maize rotations as well as back-to-back durum plantings.
“Maize is an excellent host of the FHB fungal pathogen Fusarium graminearum and if weather conditions are conducive, the fungal pathogen will release tiny ascospores that can be wind-blown over moderate distances (~ 1 km) to infect heads of surrounding cereal crops,” Dr Simpfendorfer said.
“When conditions are warm and humid, the spores will germinate and infect the plant through the flowers (anthers) which can lead to serious grain yield losses and grain quality downgrading.”
Prolonged periods (36-72 hours) of high humidity (>80%), low evaporation and temperatures from 20 to 30°C during flowering and early grain-fill produce the most favourable conditions for FHB infection.
Yield and economic losses result from sterility of the flowers and grain that is shrivelled, lightweight, low quality and prone to containing toxins such as deoxynivalenol.
Dr Simpfendorfer recommended that growers:
- avoid durum crops in areas with known high prevalence of FHB;
- avoid sowing durum into or adjacent to paddocks that contained maize the previous year;
- plant the least susceptible varieties available (although this can be difficult with durum);
- reduce FHB inoculum levels by rotating with non-grass crops, such as sunflowers, cotton, soybeans, mungbeans, chickpeas, faba beans, canola and field peas;
- vary sowing times and varieties to minimise the risk of the entire crop flowering when weather is favourable for infection; and
- use clean seed – if contaminated seed must be used, seek further advice. Grain infected with FHB is usually white and, if prolonged wet conditions occurred during grain‐fill, infected grains will take on a pink appearance. However, it should be noted that if any white or pink grains are evident, then the levels of Fusarium infection can be significantly higher than what may be indicated by visual inspection.
Dr Simpfendorfer said in-crop fungicide treatments should be considered as a ‘last resort’ management option with the only chemical registered for use in FHB control in cereals, Prosaro®, requiring a well-timed and well-executed application strategy to be effective.
“Research has shown that spraying durum wheat at flowering (GS61) was more effective and had more yield benefit than spraying seven days before flowering,” Dr Simpfendorfer said.
“The anthers (flowers) are the primary infection site for F. graminearum, so spraying before flowering provides reduced protection of these plant structures.
“Overseas research has demonstrated the importance of spray coverage in FHB control, with twin nozzles (forward and backward facing) angled to cover both sides of a wheat head and high volumes of water (≥100 L/ha) being critical to efficacy.
“Globally, wherever corn has been grown in rotation with cereals (especially durum), add successive rainy days during flowering and more often than not they’ve ended up with significant FHB issues.”
Maize growers are also being encouraged to factor Gibberella cob rot into their decisions around hybrid selection, rotations and stubble management given that the disease is caused by Gibberella zeae – the asexual state of F. graminearum and the same fungus that causes FHB in cereals. The Gibberella cob rot fungus survives from season to season on infected maize residue.
“So that has implications for maize hybrid selection as well as management of maize stubble within the farming system,” Dr Simpfendorfer said.