Fusarium head blight in cereals

Bar graph demonstrating the 'proportion of heads' produced by different crop strains.

Summary

  • Warm moist weather at and after flowering provides conditions favourable for the disease.
  • Current wheat varieties are susceptible, some more so than others. Can also infect barley.
  • Fusarium head blight on the Liverpool Plains in 1999 caused major economic losses ranging from 20 to 100 per cent of yield and serious downgrading of quality.
  • Mycotoxins that may be produced by the fungus infecting grain can have serious implications for human and animal health.
  • Inoculum levels are presently high in many paddocks on the Liverpool Plains. However, weather conditions during and after flowering will determine the extent of disease in this year's winter cereal crop.
  • Management strategies involve crop rotation, paddock selection, seed treatment and stubble management.

Symptoms

Fusarium head blight causes affected heads and sections of heads to ripen prematurely.

The first symptoms on individual florets are small brownish water-soaked spots on the glumes. This discolouration will then spread to other parts of the floret. In humid conditions a salmon pink fungal growth appears on the head.

Cause

In 1999 Gibberella zeae was the most common cause of Fusarium head blight on the Liverpool Plains. However, a number of different fungi including the crown rot fungus Fusarium pseudograminearum can cause Fusarium head blight.

Gibberella zeae infects a range of cereals and grasses and can survive on the residues of these for a number of seasons particularly under no-tillage. Spores are produced on crop residues during warm moist weather and are dispersed by wind and rain splash.

Prolonged wet and humid weather may allow secondary infection by spores produced on wheat heads. However, most infection results from spores produced on crop residues.

On maize (corn) the fungus causes stalk and ear rot, a pinkish to reddish mould appearing on the kernels.

Hosts

Wheat, barley, oats, maize, sorghum and a number of grasses are hosts of the fungus Gibberella zeae. Durum varieties appear to be more susceptible than bread wheats. In a field trial in 1999 the bread wheat varieties Sunvale, Baxter and Sunco had low levels of Fusarium head blight (see above). There is no local information on barley varieties at this time.

Management for the 2000 crop

Fortunately, to date, serious outbreaks have been infrequent in Australia. For significant losses to occur there must be:

  • inoculum present
  • a susceptible host
  • favourable environmental conditions.

Even a highly susceptible variety in a paddock with a high level of inoculum may suffer minimal Fusarium head blight if flowering coincides with a period of cool dry weather.

Inoculum levels are high in many paddocks on the Liverpool Plains although actual levels will vary as a result of previous management and crop history. The weather during and after flowering time will determine if significant disease occurs.

September and October in 1998 and 1999 were unusually wet and warm, providing two consecutive years suitable for Fusarium head blight.

Rotation to non-hosts reduces host plant residues and Fusarium head blight inoculum. Lowest-risk paddocks are those in which non-hosts have been grown in the last two seasons, although a one-year break is better than double cropping. Highest risk occurs where wheat is no-tilled into standing maize stubble.

Vary sowing times and varieties to minimise the risk of the entire crop flowering when weather is favourable for infection.

Reducing host plant residues by incorporation or burning will reduce the level of inoculum but will not eliminate it. These practices will leave paddocks prone to erosion.

Irrespective of the method of reducing stubble, it is not possible to guarantee freedom from Fusarium head blight, particularly in strip cropping where only short distances separate infected stubble and the current crop. It is believed spores from the Fusarium head blight fungus can travel these short distances.

There are no fungicides registered for control of Fusarium head blight in Australia. Research in North America with foliar fungicides applied at flowering have given varying results.

Seed treatment

Fusarium head blight is a seed-borne disease. Grading of seed, preferably on a gravity table, will improve germination and emergence.

Treatment with registered seed dressings, while unlikely to reduce seedling blight caused by Gibberella zeae, is recommended as a routine precaution to reduce bunts and smuts. Seed dressings and grading will, however, have no influence on Fusarium head blight later in the season, as the main source of inoculum will be from residues in the paddock.

Management plan for Fusarium head blight

  • keep Fusarium head blight in perspective, manage the farm as a whole
  • manage to prevent crown rot first
  • very important to avoid maize paddocks from previous year
  • avoid wheat, barley, grassy and possibly sorghum paddocks
  • plant least susceptible varieties
  • vary sowing times and varieties to minimise the risk of the entire crop flowering when weather is favourable for infection
  • use clean seed; if you have to use contaminated seed, seek advice.

Acknowledgements

This project was supported by NSW Agriculture and by growers and the Federal Government through the GRDC. We gratefully acknowledge the assistance given by Greg Giblett (agronomist), Gordon and David Brownhill (graingrowers), Warwick Fisher (grain-grower), John Kneipp (NSW Agriculture), Tony Dale (NSW Agriculture), Ray Hare (NSW Agriculture), Bob Ware (Seed and Grain IAMA for seed grading), David Coote (seed grader), Bruce Haigh (NSW Agriculture) and Paul Carberry (NSW Agriculture), Uniroyal Chemical (seed treatment products).

Further reading

Root and Crown Diseases of Wheat in Northern NSW (NSW Agriculture)

Winter Crop Variety Sowing Guide 2000 (NSW Agriculture)

program 2.6.1

Contact: Dr Kevin Moore 02 6763 1133

*This is an edited version of a NSW Agriculture research update (Agdex 110/637) Fusariurn Head Blight in Northern NSW, 2000.