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

Grazing barley controls early foliar diseases, has manageable impacts on malting barley grain quality but suffers a yield penalty. Andrea Hills 1 and Blakely Paynter 2 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 grazing of cereal crops is not a recent innovation but fell out of favour in Western Australia for many years as growers focused on grain production while livestock numbers steadily decreased. In an effort to close the winter feed gap that generally determines stocking rates, farmers in the medium and high rainfall areas of Western Australia have now started to graze cereals and then harvest grain at crop maturity. The effects of grazing on the grain quality of barley varieties grown for malting are largely unknown (Grain and Graze Workshop Notes, 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 with 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 the withholding period and potentially have a shorter grazing window or to leave disease susceptible malting barley 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? If lower levels of foliar disease are maintained to flag leaf emergence or later, this would be of considerable benefit since ungrazed barley crops with disease susceptibility often already have lesions present on the lower leaves at elongation, which then often progresses up the plant as it elongates. The aim of this study was to examine whether grazing of malting barley can adequately control foliar diseases up to stem elongation and what impact does grazing have 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. The soil was a grey, deep sandy duplex (grey chromosol) (Schoknecht, 2002). Table 1. The 2011 and average (1991 2010) monthly rainfall for Esperance Downs Research Station. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 2011 36 29 31 25 59 21 57 43 40 113 59 66 Average 45 25 34 41 55 50 55 65 54 40 34 21 Trial design: Baudin barley x ± mowing x 2 seed treatments x 2 fungicide treatments x 4 replicates. Seed treatments (applied at recommended rates): 1. Control 2. Zorro (triadimenol + imidacloprid) Registered for control of powdery mildew Foliar fungicide treatments 1. Control (no foliar fungicides applied) 2. Disease control All seed received a basal seed dressing of Dividend (difenconazole + metalaxyl-m) to suppress any rhizoctonia (R. solani) in the trial. Small plots (2 x 15m) in a strip plot, cyclic randomisation were sown to establish approximately 150 plants/m 2 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 with new cutting blades that were regularly resharpened and 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 applied to mowed and unmowed treatments was Prosaro (prothioconazole + tebuconazole) at 150 ml/ha + 1% Hasten when unmowed plants were at stem elongation, flag leaf emergence and half head emerged. Dry matter from the entire plot at each mowing was removed, dried and weighed. 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 maturity two dry matter cuts per plot were taken to determine dry matter production and the grain yield components of tiller number/m 2, grains/ear, grains/m 2 and harvest index. 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 was used to estimate grain protein content (% NIR) colour (NIR L*),and malt extract levels (%, NIR).. The GenStat 12 th edition program was employed to perform ANOVA tests. General linear regression analysis was performed on yield component data against grain yield. Results In 2011, in the south east of the West Australian agricultural region, the dominant barley leaf disease was powdery mildew with low levels of leaf rust developing later in the winter months. Baudin is very susceptible to powdery mildew and an exceptional number of foliar fungicide sprays were required in 2011: they were applied to the unmowed crop at stem elongation, flag leaf emergence and half head emerged.

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). The fungicide applied at stem elongation did not halt the development of the mildew on the mowed plants, which increased to 30% LAA, while the level of disease on unmowed plants remained the same (36 % LAA). % Leaf area affected Mowing start Mowing end 45 40 35 30 25 20 15 10 5 0 1-Jun 15-Jun 29-Jun 13-Jul 27-Jul 10-Aug 24-Aug 7-Sep 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. The effectiveness of mowing versus using a seed dressing registered to control powdery mildew couldn t be assessed as the triadimenol that was applied was ineffective. Data comparing the nil and plus triadimenol seed dressing is not included in the remaining tables and figures. Mowed plants took at least 15 days longer to reach half head emergence than unmowed plants (P < 0.001). Table 3 shows the growth stages through the season; the mowed plants were already significantly delayed by stem elongation and the developmental gap widened as the season progressed. Table 3. Plant development of mowed and unmowed barley through the 2011 season showing Zadoks scores for the corresponding growth stages. Mowed barley Unmowed barley Date Zadoks Growth stage Zadoks Growth stage 27-Jul 29 end of tillering 31 1st node 29-Aug 37 end stem elongation 50 awns emerging (>10mm) 19-Sep 55 half head emerged 71 grain filling (water ripe) 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). Mowing reduced dry matter by an average of 604 kg/ha by stem elongation and although plant development was significantly reduced, tiller numbers of mowed and unmowed plants were similar ( P = 0.05) - an average of 7.4 per plant. 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 (see 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. Foliar fungicide treatments were no disease control (nil fungicide) and disease control (foliar fungicides applied) Foliar fungicide treatment Grain quality Nil fungicide Plus fungicide Grain yield 2174 2690 Grain weight 34.7 40.6 Screenings 15.2 2.1 Mowed Protein content 12.3 12.8 Test weight 70 74 Grain colour 55.6 54 Malt extract 80.7 81.4 Grain yield 2752 3320 Grain weight 37.4 41.2 Screenings 8.6 2.7 Unmowed Protein content 12.7 13.3 Test weight 71 73 Grain colour 55.9 55 Malt extract 82.3 81.6 ANOVA P-values 5% LSD Mowing FolFung Mowing FolFung 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 Colour 0.002 0.035 0.4 0.6 Malt extract ns ns - - Mowing significantly altered yield components; the maturity dry matter levels, tiller numbers, grains per head, grains per m 2 and harvest index were all significantly affected (Table 5). Disease control significantly improved the amount of dry matter produced and grains/m 2. For both the mowed and unmowed treatments, the number of grains produced (grains/m 2 ) were strongly correlated with grain yield (Table 6). Table 5. The impact of mowing and disease control on the yield components dry matter (kg/ha), tiller numbers (tillers/m 2 ), grains/head, grain number (grains/m 2 ) and harvest index of Baudin barley and their P-values and LSD s (5%) below. Foliar fungicide treatment Yield component Nil fungicide Plus fungicide Dry matter 5,315 6,536 Tillers/m 2 309 312 Mowed Grains/head 19 20 Grains/m 2 6,285 6,640 Harvest index 0.395 0.386 Dry matter 6,431 8,144 Tillers/m 2 328 367 Unmowed Grains/head 22 22 Grains/m 2 7,378 8,066 Harvest index 0.425 0.412 ANOVA P-values 5% LSD Mowing FolFung Mowing FolFung Dry matter 0.002 0.001 709 709 Tillers/m 2 0.041 ns 35 - Grains/head 0.002 ns 1 - Grains/m 2 0.001 0.012 220 95

Harvest index 0.023 ns 2.3% - Table 6. Regression analysis of yield components on grain yield in mowed and unmowed treatments with the associated F paired value, adjusted R 2 (%) and regression equations; only significant interactions are shown. Treatment Component F. pr R 2 (%) Regression equation Mowed Grains/m 2 0.011 97 529 +0.32x Tillers/m 2 0.018 95 439 +6.64x Unmowed Dry matter 0.033 90 1927 +0.17x Grains/m 2 0.037 89 751 +0.32x 1000 kernel weight (mg, db) 44 42 40 38 36 34 32 Nil fungicide Unmowed Plus fungicide Mowed Screenings (% < 2.5 mm) 24 20 16 12 8 4 0 Nil fungicide Unmowed Plus fungicide Mowed Hectolitre weight (kg/hl) 78 76 74 72 70 68 Nil fungicide Unmowed Plus fungicide Mowed 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 This trial shows that regular mowing was able to successfully control the development of the leaf disease powdery mildew in barley until the start of stem elongation. This means that farmers who plan to graze their crops only need to apply a smut and bunt seed dressing, some of which have only four week withholding periods, which is ideal for crop grazing. This results provides the potential to achieve savings in crop inputs (fungicides) worth approximately how much/ha and maximises the time period that crop grazing is available to the grower. However, adequate stock numbers are required to uniformly graze the crop which will be a challenge in some areas of West Australia. 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. The grain yield penalty of 20 percent that occurred from mowing was avoided? if was ceased prior to stem elongation when it can reduce grain production via the removal of young shoot apices. The effects of grazing duration were not studied here but it is evident that four weeks of grazing utilising seven separate mowings was sufficient to stress the barley despite the modest amount of dry matter removed (604 kg DM /ha) and that leaves were not stripped to the white line. Given the yield component analysis, the loss in grain yield from mowing appears due to reduced dry matter production with a subsequent reduction in tiller numbers, grains per ear and grains per m 2. The reduction in tillering was more important than grains per ear in reducing grain yield because?????. The month of August, after grazing finished, was a Decile 3 year for rainfall at this site and it likely contributed to the stress experienced by the mowed plants in their recovery period. On some soil types grazing has helped to conserve soil water for use during grain fill later in the season (Virgona et al, 2006), minimising yield penalties. However, the dry spell at this site was an opportunity to demonstrate this theory, albeit indirectly measured by grain yield, but if soil water was conserved here then it was insufficient to prevent plant stress significantly reducing the grain yield of mowed plants. Indeed, the yield penalty probably would have been even worse if October, the final month of the growing season hadn t had such uncharacteristically high rainfall (Decile 10). 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, 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). Where disease control was undertaken, the average grain weight was still lower when mowed but screenings were the same for mowed and unmowed treatments alike. As Baudin is a relatively narrow grained malting variety, other varieties with grain of the same or plumper shape (all apart from Gairdner) could be expected to perform similarly so that screenings should not be affected by grazing if growers use adequate foliar disease control measures. That mowing + disease control did not affect grain hectolitre weights or grain extract levels is positive for growers (who must deliver malting grain of a given hectolitre weight) and end users such as maltsters who may look critically at any negative influence of farming practices on grain quality. The reduction of plant height from mowing has been observed in many studies including this one and for tall varieties that lodge, such as Buloke, Scope and Gairdener, potentially reducing lodging and improving grain yields. However, Baudin is short in stature and very unlikely to lodge so that grazing of Baudin in low rainfall areas instead may result in the crop being so short that it is difficult to mechanically harvest. Where disease control was undertaken, mowing did not change the relative importance of yield components such as grains per m 2. Tiller numbers of the mowed plants were a more significant contributor to grain yield than dry matter levels, possibly indicating that the rate of dry matter regrowth shortly after mowing is critical to maximise tiller survival rate. Conclusions Leaf diseases present during early vegetative growth stages of barley can be reduced by grazing so that only a seed dressing for smuts and bunts is required. 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. Further study is required into barley s recovery mechanisms and how tiller survival can be maintained under mowing regimes 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 the Esperance Downs Research Station personnel Bill Sharp and Chris Matthews, Bruce Simmonds for technical assistance during the year and Sue Cartledge for NIR data. The NIR calibrations were provided by S. Harasymow of the DAFWA Grain Products Laboratory. This work was jointly funded by the Department of Agriculture and Food, WA and the Australian Grains Research and Development Corporation; Project No DAW00190: Barley agronomy for the western region 2009 2012 References Droushiotis DN (1984) Effect of grazing simulation on forage hay and grain yiels of spring barleys in a low rainfall environment. 103: 587-594 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 grainfilling 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