INTERACTION OF NITROGEN AND FUNGICIDE APPLICATIONS FOR MANAGING YELLOW

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Interaction of Nitrogen and Fungicide applications for Managing Yellow Spot in Wheat on Wheat

Interaction of Nitrogen and Fungicide applications for Managing Yellow Spot and Stagonospora Nodorum in Wheat-on-Wheat

Ciara Beard and Anne Smith, Department of Agriculture and Food

Key Messages

Aim

Research has shown that higher rates of nitrogen generally result in lower levels of yellow spot in wheat. This may be due to a range of responses to nitrogen such as reducing the rate of lesion development or delaying natural leaf senescence, making it appear that there is less disease. Our aim was to investigate the interaction of nitrogen and fungicide in the control of yellow spot in wheat varieties of varying yellow spot resistance.

method

Treatments

Two trials were conducted, one in 2010 and one in 2011 at the Northern Sandplain Research Annexe, Eradu and located on wheat stubble. Each trial was a randomised block design with the following 12 treatments each replicated four times. Plot size was 20m x 1.54m with a barley buffer between wheat plots.

Main Treatment - Variety

1. EGA Eagle Rock (S to yellow spot, MR-MS to stagonospora nodorum)

2. Wyalkatchem (MR to yellow spot, MS-S to stagonospora nodorum)



Sub treatment – nitrogen and +/- fungicide (Tilt®)

Treatment number

2010 Nitrogen applied (1)

2011 Nitrogen applied (1)

Fungicide

Tilt® @ 500 ml/ha

At seeding

At Z32

At seeding

At Z32

1 Max N

56 kg N/ha

19 kg N/ha

37 kg N/ha

19 kg N/ha

Z32

2 Max N

56 kg N/ha

19 kg N/ha

37 kg N/ha

19 kg N/ha

-

3 Medium N

26 kg N/ha

19 kg N/ha

11 kg N/ha

19 kg N/ha

Z32

4 Medium N

26 kg N/ha

19 kg N/ha

11 kg N/ha

19 kg N/ha

-

5 Min N

26 kg N/ha

11 kg N/ha

Z32

6 Min N

26 kg N/ha

11 kg N/ha

-

  1. - Urea (containing 46%N) at seeding: Flexi-N® (containing 32 % w/w N) was applied at Z32 (stem extension).

Trials were sown by cone-seeder at 75kg/ha to achieve ~120-150 plants/m2. Herbicides were applied as necessary. Foliar application of Flexi-N® was applied in a separate application to fungicide at Z32. Fungicides were applied in 80 L water by boom. Rainfall was monitored with an electronic rain gauge at each site where possible.

In 2010, initial soil nitrogen levels before seeding were Nitrate N 9 mg/kg, Ammonium N 1mg/kg, and all plots received a basal treatment of Agstar Xtra (containing 14.9%N) applied at 80 kg/ha at seeding

In 2011 initial soil nitrogen levels before seeding were Nitrate N 2 mg/kg, Ammonium N 1mg/kg, and all plots received a basal treatment of Agras (containing 16.1%N) applied at 80 kg/ha at seeding.



Measurements

Plant emergence was determined 3-5 weeks after sowing. Necrotic leaf area was determined on top 3 to 4 leaves at fortnightly intervals from Z32 (before each foliar fungicide spray). Pathogen identification as either yellow spot or stagonospora nodorum was confirmed through AGWEST Plant Labs at two times during the season. In 2011, prior to harvest, the number of heads per metre of row was counted and heads collected and threshed to determine grain yield per head. In both 2010 and 2011, plots were harvested and grain sub-sampled for grain quality (protein, hectolitre weight, grain sievings and thousand-grain weight).

results and discussion

Disease development and identification

In 2010, disease at the site initially was an equal mixture of both stagonospora (septoria) nodorum blotch and yellow spot. Disease developed early as the trial was sown into wheat stubble, and rainfall in May and early June promoted the spread of disease spores by rainsplash. June and July were predominantly dry with only a few major rainfall events, which limited the spread of disease in the middle of the season, but disease increased in late winter with more rain and heavy dews. At Z75 glume blotch was evident at the site but pathogen identification showed yellow spot was dominating at 74% yellow spot to 24% stagonospora nodorum. Nitrogen and variety had no effect on severity of glume blotch at this time but there was significantly less disease on heads in the fungicide treated plots (2.4% on untreated and 1.7% on fungicide treated).


In 2011, disease at the site initially was 70:30 mixture of yellow spot: stagonospora nodorum. Disease developed slowly initially as there were few rain days in May and June. July and August had frequent small rainfall events which encouraged disease spread by rain splash. At Z69 the pathogen identification showed the dominant disease by then was stagonospora nodorum (78% to 22% yellow spot) and glume blotch was evident. There was significantly less glume blotch on the fungicide treated Wyalkatchem plots (2%) than the untreated EGA Eagle rock plots that had low nitrogen (3.5%).


Disease levels

At each disease assessment time on both trials:


As expected EGA Eagle Rock had the most disease of the two varieties, and the application of Tilt® at Z32 significantly reduced disease levels (Figure 1). In both years, up until Z55 (ear half emerged) higher nitrogen levels in conjunction with fungicide significantly reduced disease levels on both EGA Eagle Rock and Wyalkatchem. In the absence of fungicide, the medium and maximum nitrogen applications resulted in reduced disease on EGA Eagle Rock at some times. Wyalkatchem did not always respond to nitrogen but there was a fungicide response, which was determined by the dominant disease at the end of the season. In 2011 when stagonospora nodorum was dominating at the end of the season Wyalkatchem was moderately susceptible so it developed more disease than in 2010 and responded significantly to fungicide in low nitrogen treatments (Figure 1). INTERACTION OF NITROGEN AND FUNGICIDE APPLICATIONS FOR MANAGING YELLOW Figure 1. Average percentage leaf area diseased on top three leaves at Z69, EGA Eagle Rock and Wyalkatchem under three nitrogen regimes on wheat stubble at Eradu in 2010 at Z55, Z69 and Z83 (top) and 2011 at Z39, Z59 and Z69 (bottom).


Yield

In 2010, only the maximum nitrogen treatment increased yield of Wyalkatchem (0.4 t/ha). EGA Eagle Rock had significant yield increases of 0.4 t/ha from both the medium and maximum nitrogen levels applied in conjunction with fungicide (Table 1).



In 2011, yield of Wyalkatchem was significantly greater (0.4 t/ha) when fungicide was applied to plants in the low nitrogen treatment. This may be because stagonospora nodorum was dominating at the end of the season and Wyalkatchem is moderately susceptible to this disease. The medium and maximum nitrogen levels also significantly increased the yield of Wyalkatchem, as expected, by 0.4 and 0.9 t/ha respectively. Yield of EGA Eagle rock was significantly increased by fungicide alone (0.3 t/ha on average), nitrogen alone (0.5 t/ha on average) and application of the two together (0.8 t/ha on average, Table 1).



Wyalkatchem yields were higher than EGA Eagle Rock in both years. In 2011, both varieties were more responsive to nitrogen, likely due to the lower initial nitrogen levels and the higher than average rainfall creating a better growing season. Nitrogen application increased tiller number and head dry weight on EGA Eagle Rock. For Wyalkatchem, only the maximum nitrogen treatment significantly increased tiller number and head dry weight. Only the maximum nitrogen treatment significantly increased seed weight of both varieties.


Table 1. Yield of EGA EagleRock and Wyalkatchem under three nitrogen regimes on wheat stubble at Eradu in 2010 and 2011.



Yield 2010

Yield 2011

Variety

Nitrogen

Nil Fungicide

Fungicide at Z32

Nil Fungicide

Fungicide at Z32

EGA EagleRock

Min N

1.9

1.9

2.3

2.5

Medium N

2.0

2.2

2.6

2.9

Max N

2.0

2.3

3.0

3.3

Wyalkatchem

Min N

2.3

2.4

2.7

3.2

Medium N

2.4

2.6

3.2

3.1

Max N

2.6

2.8

3.7

3.7

LSD (5%)

0.233

0.200




CONCLUSION

The results of this trial suggest that nitrogen and fungicide are each effective on their own, and also in combination, for managing leaf spot diseases on susceptible wheat varieties. Nitrogen application increases the vigour of wheat plants and number of tillers and thus can increase yield and may allow for fungicide application to be more effective, particularly on susceptible wheat varieties. This highlights the importance of employing optimum nitrogen nutrition in order to maximise fungicide return for susceptible varieties.


In both these trials EGA Eagle Rock responded positively when fungicide was added in conjunction with a high level of nitrogen, indicating that this combination may give added disease control to a susceptible variety.


This research has found that yield of moderately resistant varieties will not respond to a combination of nitrogen and fungicide but may respond significantly to additional nitrogen on its own. In a situation where nitrogen levels are inadequate, then they may respond to fungicide on its own, particularly if a disease, to which the variety is moderately susceptible, strikes late in the growing season.

Key words

Nitrogen, Fungicide, Wheat, Disease

acknowledgments

GRDC for funding the research, DAFWA Geraldton Research Support Unit for seeding and harvesting trials.


GRDC Project No.: DAW00210

Paper reviewed by: Bill MacLeod


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