The Imtrader Ed.2 – Powdery Mildew

 

Trial by Michael Macpherson (National Technical Manager, Imtrade) & Elly Wainwright (R&D Coordinator, Liebe Group)

 

Powdery Mildew Blumeria graminis f. sp. hordei has traditionally been a yearly fungal disease in higher rainfall zones on barley crops across most cropping regions. Powdery mildew of wheat Blumeria graminis f. sp. tritici is generally not as common and considered less likely to infect at threshold levels.

Powdery Mildew in Mace Wheat

In the 2015 growing season, alarming levels of wheat powdery mildew were found to be infecting crops across the northern wheatbelt of WA, noticeably worse on white sandplain compared to red loams or other soil types. The resultant infection of the northern wheat crop led growers to apply up to 3 foliar applications of fungicide to their crops. Generally the fungicide of choice was tebuconazole in most situations.

In response to the situation, Imtrade Australia in conjunction with the Liebe Group implemented a fungicide trial in West Buntine to investigate various chemistries for effectiveness on powdery mildew. As part of this investigation, granular tebuconazole was directly compared to liquid tebuconazole to demonstrate the equivalent efficacy of the new granular product to the traditional liquid formulation.

 

Trial Details

 

Treatment List

*All treatments applied at 87L/ha with the addition of 200mL/100L of Wetter 1000.

Results:

Incidence = average presence of disease on nominated leaf as a percentage infected per plot.

Severity = average percentage of leaf area infected on nominated leaf per plot.

DAT = days after treatment

 

Comparison of treatment means. Powdery Mildew on grain head:

 

Comparison of treatment means. Powdery Mildew Flag Leaf:

*ns – no statistical significance at p <0.05.

*Means within the same cell with a letter in common are not significantly different (P<0.05)

 

Comparison of treatment means. Powdery Mildew Flag-1 Leaf:

*ns – no statistical significance at p <0.05.

*Means within the same cell with a letter in common are not significantly different (P<0.05)

 

Comparison of treatment means. Powdery Mildew Flag-2 Leaf:

*ns – no statistical significance at p <0.05.

*Means within the same cell with a letter in common are not significantly different (P<0.05)

 

Comparison of treatment means. Powdery Mildew Flag-3 Leaf

*ns – no statistical significance at p <0.05.

*Means within the same cell with a letter in common are not significantly different (P<0.05)

 

Comments

Effective fungicidal treatments will prevent disease progressing up the tiller (reduced incidence scores compared to untreated on upper leaves) and reduce the severity of infection on pre-treatment infected leaves (lower severity rating compared to the untreated but with similar incidence percentage).

This is clearly demonstrated in the results, with the application of all fungicidal treatments providing a statistical difference in both the incidence and severity of powdery mildew infection on Flag-1 compared to the untreated, with Triadimefon, Radial, Amistar Xtra and Cogito exhibiting the best response. Flag-2 exhibited statistical significance for the severity of infection with Triadimefon, Turbulence 800, Tebuconazole 430, Cracker Jack 550 and Radial all reducing the severity; incidence of disease presence was non-significant on this leaf.

All treatments provided significant control of powdery mildew on the flag leaf compared to the untreated. However, there were no significant differences between treatments in the severity or incidence on the Flag or Flag-3 leaves. Progression of the disease post application up the tiller is clearly demonstrated in the untreated control, with higher incidence and severity scores lower down the tiller (Flag-3 scores are lower due to complete leaf senescence rendering it un-assessable and returning a 0 score).

The granular formulation of tebuconazole exhibited statistically equivalent control and prevention of wheat powdery mildew across all timings and assessments compared to the liquid formulation.

The data clearly demonstrates the 4 week physiological efficacy of most fungicides. The 42 DAT assessment has shown the decline in fungicide efficacy due to waning residual in the target leaves, however still exhibits significant differences between treatments. The heads have not been sufficiently protected, as demonstrated by NS for incidence and higher incidence compared to protected leaves. This is expected from a fungicide application at booting (most heads still in flag sheath) as minimal systemic activity is experienced from most fungicides away from treated leaves (not translocated acropetally) so non-contacted parts of cereals are not protected by earlier applications therefore 2-3 sprays per season may be required to protect new growth.

It should be noted that due to the extremely high virulence of powdery mildew, rapid resistance to fungicidal chemistries can develop. Always implement a rotation strategy within your fungicidal program. The results obtained from this trial will not necessarily be reflective of every situation, dependant on the resistance profile of powdery mildew pathotypes in your area.

 

Acknowledgements:

  •  The Liebe Group for assisting with the implementation and monitoring of the trial.
  • The Bryant family for hosting the trial.