| | Fusarium graminearum (Fg) is a serious fungal disease of cereal grains that affects yield and grade, resulting in poor quality grain intended for feed, malting, milling, and the biofuel industry. Recent surveys indicate Fg is established in southern Alberta and traces are present in central and northern regions of the province. Although all cereal crops are susceptible, durum and corn are major hosts.
..
Fg can be effectively controlled under normal conditions using a combination of disease prevention strategies throughout the growing season. The use of a single strategy usually fails when weather conditions are favourable for infection. During the growing season, strategies include careful herbicide applications, irrigation management and an in-crop fungicide application if risk levels are moderate to high.
Cereal crops are most vulnerable to new Fg infection at flowering time if weather conditions are moist and warm. Disease spores are spread by rain splashes and wind to infect open flowers. If possible, irrigation during flowering should be avoided.
Grain heads that rapidly and uniformly pass through the flowering period are least susceptible, so prevention of crop injury during post-emergent herbicide applications is important to prevent uneven crop maturity. Variable maturity extends the flowering period, thus leaving the crop open to a longer infection period, prolonging the irrigation break and reducing fungicide performance.
Observable Fg symptoms don’t appear until the late heading stage when it is too late to apply protective fungicide. A decision to apply a fungicide must be made prior to this, at the early flowering stage. Disease risk level increases when more of the following factors exist:
- field is located in a region where Fg is established,
- cereal variety being grown is susceptible to Fg,
- durum or corn is in the crop rotation,
- cereal crops are frequently grown in the same field or in nearby fields,
- weather conditions are damp and warm at crop flowering stage,
- irrigation is used in the farm operation,
- yield potential is good,
- cereal grain prices are high.
If the risk level is assessed as moderate to high and yield return justifies fungicide application cost, a foliar fungicide application should be applied at early flowering to protect open florets. Application of fungicide too early is better than too late.
With wheat, flowering begins 3 to 4 days after head emergence and lasts approximately 7 days. The optimum stage for fungicide application is during early flowering when some visible anthers are present on the head, so begin watching closely when the wheat head begins to emerge from the boot.
With barley, flowering begins just prior to head emergence and continues during heading, lasting approximately 14 days. The optimum stage for fungicide application is when the spike is fully emerged from the boot, so begin watching when the first spikelet emerges from the boot.
Studies indicate that FHB control is improved by directing spray nozzles at 30 degrees from the horizontal either forward or backward or simultaneously forward and backward, and use a high water volume to optimally cover grain heads. While 10 gallons (45 litres) per acre of water is adequate for spring wheat, 18 gallons (80 litres) per acre are recommended for durum as durum grain heads are more difficult to wet.
The most apparent Fg disease symptom is premature bleaching or blighting of one or more spikelets in the head, which stands out on green heads (see picture). Under prolonged humid conditions, orange-coloured fungal spores appear on blighted parts of the head. If humid conditions persist, the pathogen can cause higher mycotoxin levels by spreading to other kernels and heads after seed set.
Foliar Fungicide options: Folicur, Proline, Bravo, Caramba, Prosaro.
Barley – Caramba, Proline, Prosaro.
Wheat – Bravo, Caramba, Folicur, Proline, Prosaro.
Neil W. May 2013 |
|