Flag-leaf timing best for fungicide application in malt barley

For improved leaf disease management and yield in malt barley, fungicide applications should include a flag leaf stage timing or later for adequate protection of upper canopy leaves, which are key contributors to yield and grain filling. A tank-mix of a one-half rate fungicide with a herbicide application at the 2 to 3 leaf stage resulted in higher disease pressure, and lower yield and quality than a flag leaf fungicide application.

The interest in tank mixing fungicides with herbicides and applying at an early weed control timing is an opportunity for a convenient one-pass control of  weeds and diseases. At the time this research was conducted from 2010 to 2012, little information existed regarding the effect of early versus mid-season application of fungicides and the impact on barley yield and kernel quality. The underlying factors/principles of this research are still at relevant today.

The objective of this study was to determine the effects of herbicide and fungicide timings on barley leaf disease severity, and the yield and kernel quality of the malting barley cultivar AC Metcalfe.

The research was conducted at 6 sites across the Canadian Prairies at Lacombe, and Lethbridge, Alberta; Scott, Melfort and Indian Head, Saskatchewan; and Brandon, Manitoba. The study was conducted over three growing seasons at each site. However, trials at Brandon and Lethbridge were not conducted in 2010 and 2011 due to flooding, nor at Indian Head in 2010 due to a lack of suitable field space.

AC Metcalfe malt barley, which is susceptible to scald and net-form net blotch, and moderately resistant to moderately susceptible (intermediate) to spot-form net blotch, was seeded at a target rate of 30 seeds/ft² (300 seeds/m²). No-till drills with knife openers with a seedbed utilization of approximately 10% were used. To ensure uniform weed pressure the plots were cross-seeded with tame oat at a rate of 10 seeds/ft² (100 seeds/m²).

The following herbicide/fungicide treatments were applied:

1. No fungicide, herbicide applied at the 2- to 3- leaf growth stage (Check)
2. No fungicide, herbicide applied at the 5- to 6- leaf growth stage (Check)
3. Half-rate fungicide tank mixed with herbicide applied at the 2- to 3-leaf growth stage
4. Half-rate fungicide tank mixed with herbicide applied at the 5- to 6-leaf growth stage
5. Full rate fungicide applied at the flag leaf stage and only herbicide applied at the 2- to 3-leaf growth stage
6. Full rate fungicide applied at the flag leaf stage and only herbicide applied at the 5- to 6-leaf growth stage
7. Half-rate fungicide and herbicide applied at the 2- to 3-leaf growth stage followed by a full rate application of fungicide at the flag leaf growth stage
8. Half-rate fungicide and herbicide applied at the 5- to 6-leaf stage followed by a full rate of application fungicide at flag leaf growth stage
9. Half-rate fungicide and herbicide applied at the 2- to 3-leaf stage of crop followed by a half- rate application of fungicide at the flag leaf growth stage
10. Half-rate fungicide and herbicide applied at the 5- to 6-leaf stage of crop followed by a half- rate application of fungicide at flag leaf growth stage

 

When the fungicide was tank-mixed with the herbicide, Tilt 250E (Propiconazole 250 g/L) was applied at 62.5 g a.i./ha (half rate) with 100 L/ha of water. For the flag leaf stage fungicide treatments, Tilt 250E was applied at 125 g a.i./ha (full rate), or 62.5 g a.i./ha (half rate) with 200 to 224 L/ha of water depending on the treatment.

Upper canopy leaf samples were collected for leaf disease assessment at the early dough growth stage. Weed biomass, grain yield and quality were determined.

Early fungicide treatments ineffective

Fungicide and herbicide treatment combinations had significantly higher total leaf area diseased. Half-rates of fungicide applied with a herbicide at the 2- to 3-leaf stage did not significantly reduce leaf disease compared to the 2- to 3-leaf stage herbicide-only check. There was a small reduction in leaf disease when the half rate of fungicide was applied with the herbicide at the 5- to 6-leaf stage versus the 5- to 6-leaf stage herbicide-only treatment.

Leaf disease was significantly lower with the full rate fungicide applied at the flag leaf stage compared with the no-fungicide checks or the half-rates of fungicide applied with the herbicide at either the 2- to 3-leaf or 5- to 6-leaf stage.

Early weed control beneficial

Weed control was excellent at all sites so weed biomass was generally not affected by the treatments. However, yield was lower when herbicide was applied at the 5- to 6-leaf versus the 2- to 3-leaf stage.  This was due to increased weed interference when the herbicide application was delayed to the 5- to 6-leaf stage.

Flag leaf fungicide application produced the highest yield and quality

Yield, 1000-kernel weight, kernel plumpness and test weight were greatest and kernel thins lowest for treatments with a flag leaf stage fungicide application. Fungicide applications earlier in the growing season, when herbicides are typically applied, had much less impact on upper canopy leaf disease, and subsequent yield and kernel quality.

For example, Treatment 5 of herbicide-only application at the 2- to 3-leaf stage plus full rate fungicide at the flag leaf stage yielded 81 bu/ac (4.36 t/ha), with 83% plumps, 3.1% thins, 40 g TKW, and 62.3 kg/hl test weight. This compared to Treatment 3 of herbicide application plus one-half rate fungicide at 2- to 3-leaf stage yielding 73.3 bu/ac (3.94 t/ha), with 76.2% plumps, 3.3% thins, 37.3 g TKW, and 60.7 kg/hL test weight. The yield and quality responses to Treatment 5 would be attributed to improved disease control at the flag leaf stage compared to one-half rate at herbicide timing.

Ultimately, when using an in-crop fungicide for cereal leaf disease control, the researchers found that protection of the upper canopy leaves should be the primary goal as this permits a longer period of grain filling, leading to higher grain yield, kernel weight, plumpness, and test weight. Upper canopy leaf protection with fungicide should be combined with early-season weed removal using herbicides to minimize the impact of leaf diseases and weeds and to promote high and less-variable grain yields.

Earlier fungicide applications at a herbicide timing provided limited benefits as subsequent leaves that emerge post-application are not protected.  Moreover, given the nature of the fungicides available they are only effective on fully emerged leaves, while protection is for about two weeks and typically do not eradicate leaf spot pathogens from well-established infections.  Finally, leaf spot inocula (spores) are still available from previous barley residues, and older active leaf infections about two weeks after fungicide application.

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The researchers are grateful to the Western Grains Research Foundation, Alberta Barley Commission, the Canadian Wheat Board, and RAHR Malting Canada Ltd. for the financial support that they have committed to this project as part of the Agriculture and Agri-Food Canada (AAFC) DIAP program as well as AAFC support via A-Base resources.

Turkington, T. K., O’Donovan, J. T., Harker, K. N., Xi, K., Blackshaw, R. E., Johnson, E. N., Peng, G., Kutcher, H. R.,May, W. E., Lafond, G. P., Mohr, R. M., Irvine, R. B. and Stevenson, C. 2015. The impact of fungicide and herbicide timing on foliar disease severity, and barley productivity and quality. Can. J. Plant Sci. 95: 525537.

OPEN ACCESS: https://cdnsciencepub.com/doi/pdf/10.4141/cjps-2014-364