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Grazing barley controls early foliar diseases, has manageable impacts on malting barley grain quality but suffers a yield penalty.

Andrea Hills1 and Blakely Paynter2

1 Department of Agriculture and Food WA, Esperance 6450. Email andrea.hills@agric.wa.gov.au
2 Department of Agriculture and Food WA, Northam 6401.

Abstract

Crop grazing is being re-examined by farmers for integration into mixed farms in the medium - high rainfall areas of Western Australia. Control of foliar disease has been suggested as an advantage of grazing barley crops but this has not been thoroughly tested. The impact of grazing on malting quality is also largely unknown. In this study, the popular West Australian malting barley, Baudin, was grown in small plots and received simulated grazing via mowing for five weeks until stem elongation. Mowing successfully reduced disease levels until the start of stem elongation. Disease control was required to minimise the impact of mowing on grain yield and quality. Overall, mowing caused grain yield to decrease by 604 kg/ha or 20 per cent of unmowed yield. Mowing reduced grain weight and protein and the grain was darker. Malt extract levels were unaffected, as were 2.5 mm screenings where disease control was applied. Most aspects of grain quality of grazed barley can be managed by growers. The specific environmental or grazing management factors causing yield penalties however remains unknown.

Introduction

The effects of grazing barley crops on the grain quality of malting varieties are largely unknown (Anonymous, 2008) although the flowering date of barley is delayed by grazing (Martin and Knight – 1987; Winter and Thompson 1987; Scott and Hines 1991; Anonymous 2008; Anonymous, 2009) and would presumably affect grain filling in a Mediterranean environment unless soil moisture levels during spring are conserved by grazing as some have speculated (Virgona et al, 2006; Anonymous, 2009). Martin and Knight (1987) grew the malting barley Triumph under irrigation and observed that after grazing to Z31, fine extract levels remained the same with an April sowing but fell significantly with May and June sowings. Other grain quality parameters such as protein, grain weight and 2.37 mm screenings did not show any consistent pattern. At Inverleigh in Victoria, grazing consistently decreased grain protein regardless of a range of nitrogen applications while the impact of grazing on other grain quality characteristics of barley was “unclear” (Anonymous 2008).

The question of which seed fungicide to apply if grazing barley, is also important; most of those registered in Western Australia potentially limit early grazing opportunities through long withholding periods for grazing, eg. Zorro nine weeks post sowing, Baytan five weeks post sowing while other products which are active against smuts and bunts and not necessarily leaf diseases have a shorter grazing withholding period, such as Raxil, four weeks post sowing and Intake Combi (applied to fertiliser) four weeks post sowing. Farmers are loath to either break withholding periods, which results in a shorter grazing window, or to leave disease susceptible varieties exposed to leaf diseases early in growth. Grazing may offer a solution to this situation; with near defoliation of plants, it can reasonably be expected that the level of leaf disease present may be negligible or at least lower immediately after grazing than in an ungrazed crop. If disease levels are lower at elongation then for how long does this advantage persist?

The aim of this study was to examine whether grazing of malting barley can adequately control foliar diseases up to stem elongation and the impact grazing has on malting grain yield and quality.

Methods

The trial was grown at Gibson on the Esperance Downs Research Station (E121 21’ 54”, S33 16’ 97”); 35km north of Esperance in a high rainfall area where the foliar diseases powdery mildew and barley leaf rust are common. The growing season rainfall from May to October 2011 was 335 mm with a marked increase from the average in October (113 mm versus the average of 40 mm). The soil was a grey, deep sandy duplex (grey chromosol) (Schoknecht, 2002).

The trial design was; Baudin barley x mowing x 2 fungicide treatments x 4 replicates where the foliar fungicide treatments were either nil (no disease control) or plus fungicide (foliar fungicide applied).

All seed received a basal seed dressing of Dividend (difenconazole + metalaxyl-m) to suppress rhizoctonia (R. solani) present. Small plots (2 x 15m) in a strip plot, cyclic randomisation were sown to establish approximately 150 plants/m2 at a row spacing of 24 cm on 11 May 2011 and ‘grazed’ using a lawn mower once the plants were anchored at four weeks after sowing (13 June) when plants were in early tillering. The crop was sown with a banded compound fertiliser with additional fertiliser topdressed at sowing and again one week after mowing finished so that the crop received a total of 80 kg nitrogen per hectare. The lawn mower that simulated grazing was a Rover set at the minimum level of around 3 cm above level ground. Mowing continued approximately every five days until just before the start of stem elongation on 19 July, giving five weeks of ‘grazing’ from seven mowings. The fungicide used for disease control in mowed and unmowed treatments was Prosaro (prothioconazole + tebuconazole) at 150 ml/ha + 1% Hasten and applied when unmowed plants were at stem elongation, flag leaf emergence and half head emerged.

Leaf diseases were assessed by sampling ten main stems per plot, estimating the percentage of leaf area diseased and apportioning it to each disease present. This was done on either the top two fully emerged leaves (before flag leaf emergence) or the two leaves beneath the flag leaf (F-1, F-2). Plant development (zadoks score) was also recorded during disease assessments. The assessments were done when the unmowed plants were at the start of stem elongation (27 July), flag leaf emergence (29 August) and awn peep (13 September).

At grain maturity (23 November 2011), grain yields and samples for quality analysis were collected and 2.5 mm screenings (% below 2.5 mm), hectolitre / test weight (kg/hL) and 1000 grain weight (mg, db) were measured. NIR estimated grain protein content (% NIR) colour (NIR L*), and malt extract levels (%, NIR).

The GenStat 12th edition program was employed to perform ANOVA tests.

Results

In 2011, in south east West Australia, the dominant barley leaf disease was powdery mildew with low levels of leaf rust developing later in the winter months. The disease pressure was severe and ongoing and Baudin is very susceptible to powdery mildew.

The development of powdery mildew in the mowed treatments accelerated after mowing ceased on 13 July (Figure 1). Two weeks after mowing finished, the mowed plants were approaching first node (Z29) and six percent leaf area affected (LAA) was infected by disease, which is slightly above the traditional threshold disease level for application of foliar fungicides (5 % LAA).

Figure 1. Powdery mildew development on Baudin barley on mowed (๐) and unmowed(▪) areas with the mowing period shown. Disease assessments were done at first node, flag leaf emerged and awn peep. The traditional fungicide spraying threshold for powdery mildew (5%) is the dashed line.

Mowed plants took at least 15 days longer to reach half head emergence than unmowed plants (P < 0.001). Despite applying foliar fungicide, disease control overall in this trial was poor (Figure 1), probably due to control plots (nil fungicide) producing copious quantities of spores which reinfected the adjacent treated plots. Even with reduced efficacy, disease control still increased grain yields in mowed plots (Table 4).

At maturity, mowing reduced average plant height by 9 cm or 17% (P <0.001). Grain yield, grain weight and 2.5 mm screenings were all significantly lower in the mowed treatments, as was colour (Table 4). The grain test weight was unchanged by mowing although there was a significant interaction with disease control so that the test weight was improved where the barley had been mowed and disease controlled (Figure 3c). Grain extract levels were not affected by mowing (Table 4). Interactions with disease control for screenings and grain weight improved the quality of mowed grain (Figure 3a, b). On average, mowing lowered grain colour by 0.4 points ; disease control had a similar effect on colour(Table 4).

Table 4. The impact of mowing and disease control on grain yield (kg/ha), grain weight (mg, db), screenings (% <2.5 mm), protein content (%, NIR), hectolitre weight (kg/hL), colour (NIR L *) and malt extract (%, NIR) with associated P-values and LSD’s (5%) below.

 

Mowed

Unmowed

 

Foliar fungicide treatment

 

Nil fungicide

Disease control

Nil fungicide

Disease control

Grain yield

2174

2690

2752

3320

Grain weight

34.7

40.6

37.4

41.2

Screenings

15.2

2.1

8.6

2.7

Protein content

12.3

12.8

12.7

13.3

Test weight

70

74

71

73

Grain colour

55.6

54

55.9

55

Malt extract

80.7

81.4

82.3

81.6

 

ANOVA P-values

5% LSD

 

Mowing

Fung

Mowing

Fung

Grain yield

<.001

<.001

197

110

Grain weight

0.002

0.003

0.8

1.8

Screenings

0.015

0.01

2

5

Protein content

0.018

ns

0.3

-

Test weight

ns

<.001

-

1

Grain colour

0.002

0.035

0.4

0.6

Malt extract

ns

ns

-

-

a)

b)

c)

Figure 3. The interaction of mowing with no (nil fungicide) or plus disease control (plus fungicide) on a) the average grain weight, b) 2.5 mm screenings and c) hectolitre weight.

Discussion and Conclusions

Leaf diseases present during early vegetative growth stages of barley can be controlled by grazing so that only a seed dressing for smuts and bunts is required. Hence, farmers who plan to graze their crops only need to apply a smut and bunt seed dressing, many of which have only four week withholding period, which is ideal for crop grazing. The benefit from this type of disease control may last even past than the two weeks post mowing observed here and into stem elongation as the disease pressure was severe and ongoing in 2011 at this site.

Physiologically, the greatest impact of mowing was a delay in developmental of approximately two weeks which, although this is one of the longest delays reported, it has been frequently observed (Martin and Knight – 1987; Winter and Thompson 1987; Scott and Hines 1991; Virgona et al 2006; GRDC Free Food for Thought – March, 2008; GRDC Factsheet – July, 2009). In an early sowing situation (such as April) this may not be a problem as the flowering and grain filling period will take place at their normal date; indeed, in this situation a delay following grazing may assist to avoid frost damage in inland areas. However, with a normal sowing date (mid May - early June) a delay in flowering is not expected to be beneficial as it moves grain filling into the hotter, drier period of the year (Jenkyn and Anilkumar, 1990; GRDC Factsheet, 2009).

Grain malt extract levels remained unaffected by mowing. When disease control measures are implemented, the hectolitre weight and grain screenings do not differ between mowed and unmowed plants. Reductions in protein content from mowing should also be manageable with additional applications of nitrogen fertiliser although the cost of this offsets grazing benefits. Hence, while most aspects of grain quality can be maintained under a grazing system, it is primarily whether the grain yield can be and at this site and in this season, there was a penalty.

The reduction of plant height from mowing was observed in this and many other studies so for tall varieties that lodge, such as Buloke, Scope and Gairdener, this tends to reduce lodging, improving grain yield.

Further study is required into barley’s recovery mechanisms, including the minimum amount of dry matter required at the start of stem elongation to minimise yield losses in the West Australian environment.

Acknowledgements

Thanks to Esperance Downs Research Station personnel Bill Sharp and Chris Matthews, Bruce Simmonds for technical assistance and Sue Cartledge for NIR data. NIR calibrations were provided by S. Harasymow of the DAFWA Grain Products Laboratory. This work was jointly funded by DAFWA and the GRDC; Project No DAW00190: “Barley agronomy for the western region 2009 – 2012”.

References

Anonymous (2009) GRDC Factsheet ”Duel purpose crops”, 2009 www.grdc.com.au

Anonymous (2008) Grain and Graze Worshop Notes “Free food for thought”, published by GRDC

Jenkyn JF and TB Anilkumar (1990) Effects of defoliation at different growth stages and in different grain-filling environments on the growth and yield of spring barley. Ann. Appl Biol. 116:591-599

Martin RJ and TL Knight (1987) Effect of date of defoliation on yield of autumn barley sown on different dates. Proc. Agron Soc NZ:, 17: 85-88

Schoknecht N (2002) Soil groups of Western Australia, WA Dept Agriculture Technical Report 246 (Edition 3) ISSN 1039-7205

Scott WR and SE Hines (1991) Effects of grazing on grain yield of winter barley and triticale: the position of the apical dome relative to the soil surface. NZ J. Ag. Res. 34: 177-184

Virgona JM, FAJ Gummer and JF Angus (2006) Effects of grazing on wheat growth, yield, development, water use and nitrogen use. Aust J Agric Res. 57: 1307-1319

Winter SR and EK Thompson (1987) Grazing duration effects on wheat growth and grain yield. Agron. J. 79:110-114

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