Autumn Round-Up Meeting 2021 - Wednesday 21 April, Gore - the Foundation for Arable ...

Autumn Round-Up
 Meeting 2021

 Wednesday 21 April, Gore

© Foundation for Arable Research (FAR)
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Table of Contents

Wheat cultivar performance in 2020-2021…………………………………………………………………….. 4
Wheat cultivar choice for disease management…………………………………………………………….. 7
BYDV management………………………………………………………………………………………………………... 13
Ramularia leaf spot management in barley……………………………………………………………………. 16
Cereal nitrogen use efficiency………………………………………………………………………………………… 19
Herbicide resistance survey and ryegrass management in cereals…………………………………. 23
Grass grub……………………………………………………………………………………………………………………… 27

 3

Wheat cultivar performance in 2020-2021
Tabitha Armour and Jo Drummond (FAR)
Key points
 • Performance of autumn sown feed and biscuit wheat, and barley were assessed in
 Southland as part of ongoing cultivar performance trials.
 • Yields were average to below average; feed and biscuit wheat reached 10.0 t/ha compared
 with a four-year average of 10.0 t/ha.
 • Yields for autumn barley averaged 7.6 t/ha compared with a four-year average of 8.0 t/ha,
 while spring barley yields reached 8.4 t/ha compared with a three-year average of 8.0 t/ha.
Southland results
Wheat
Yields of autumn sown feed and biscuit wheat produced at the Oreti trial site were average, reaching
10.0 t/ha compared with the four-year mean of 10.0 t/ha for Southland. The Balfour site was not
drilled due to Covid19 restrictions. Solar radiation through grain fill, while slightly below average,
was around 12% higher than last year at the Oreti trial site. The weekly solar radiation accumulation
data in Figure 1, comes from FAR’s interactive weather tool, which is available to growers on website
far.hortplus.com or by searching ‘weather’ on the FAR website www.far.org.nz .

Figure 1. Accumulated weekly solar radiation for Gore between October and April 2019-20 and
2020-21 relative to the seasonal average. Source: FAR Interactive Weather Platform
Figure 2 shows that the current four-year adjusted mean yields for Southland are greatest for a
range of cultivars, although Balfour only contributes three-year means to this analysis as a result of
not being drilled in the 2020-21 season. KFW1902, KFW1903 and RGT Universe were included in
CPT2 for the first time in 2020-21, so their means reflect this.

 4

Firelight
 Voltron (KWW78) B
 Graham
 Gleam (SY114257)
 KWW83
 CRWT245 BR
 LG Tapestry (KFW1903)
 CRWT233
 Reflection
 RGT Universe (SFR86-096)
 LG Typhoon (KFW1902)
 Wakanui
 Kerrin (CK121)
 Starfire
 Torch
 Ignite B
 85 90 95 100 105 110 115 120
 Yield (100 - 10 t/ha) LSD = 9

Figure 2. Autumn sown feed and biscuit wheat four*-year adjusted means (relative to a site mean
yield of 100) for Southland (mean yield = 10.0 t/ha). *Balfour site = 3-year mean.
Barley
Autumn barley produced a yield of 7.6 t/ha compared with the four-year average of 8.0 t/ha for
Southland.
Figure 3 shows the current four-year adjusted mean yields for autumn barley. Several cultivars were
in the highest yielding statistical group. The new cultivars CRBA164, SYN416-756 and 417-021 were
included in CPT2 trials for the first time in 2020-21, so their means reflect this. CRBA164, SYN416-
756 and 417-021 are feed varieties with high yield and malting potential.

 SYN416-708
 SY Silhouette
 SYN416-756
 SYN415-586
 CRBA164
 SYN417-021
 SYN415-584
 Laureate
 Buttress
 Tavern
 RGT Planet
 Jimpy
 Fortitude

 85 90 95 100 105 110 115 120
 Yield (100 = 8.0 t/ha) LSD = 12

Figure 3. Adjusted means for autumn sown barley in Southland (relative to a site mean of 100, mean
yield 8.0 t/ha).

 5

Spring barley produced a yield of 8.4 t/ha compared with a three-year average of 8.0 t/ha for
Southland. Trials in the 2019-20 season were not harvested due to Covid19 restrictions.
Figure 4 shows the current three-year adjusted means for spring barley are highest for SYN416-708
and CRBA162. These varieties were included in CPT2 for the first time, so their means reflect this.

 SYN416-708*
 CRBA162*
 SYN415-586*
 SYN417-021*
 SYN416-756*
 SY Silhouette
 Laureate
 SYN415-584
 CRBA164*
 Buttress
 Milford
 Fortitude
 Sanette
 Shada
 RGT Planet

 85 90 95 100 105 110 115 120
 Yield (100 = 8.0 t/ha) LSD = 5

Figure 4. Adjusted means for spring sown barley in Southland (relative to a site mean of 100, mean
yield 8.0 t/ha). *adjusted means are for less than three years of data.

 6

Wheat cultivar choice for disease management
Jo Drummond (FAR)
Key points
 • Cultivar resistance continues to provide the foundation for disease control.
 • Selection of, at least, a moderately resistant variety provided flexibility in fungicide
 programme choice under low-moderate disease pressure conditions at Clinton in 2020-21.
 • There was no yield response to fungicide, with a net loss on fungicide spend for most
 treatments.
 • Disease control results demonstrated how new products can be incorporated into fungicide
 programmes;
 o Care must be taken to protect new actives along with existing chemistry.
 • In Canterbury trials, the mostly resistant cultivar, Firelight, suffered an average yield loss
 under irrigation of 0.6 t/ha (5%) if fungicides were not applied, whereas yield of the more
 susceptible cv. Starfire was reduced by up to 4.7 t/ha (39%).
 • Average yield losses without fungicide were 0.4 t/ha (5%) for cv. Firelight, 1.4 t/ha (17%) for
 cv. Graham and 1.6 t/ha (21%) for cv. Starfire under dryland conditions.
 • Analysis of economic returns in all trials demonstrated the importance of tailoring fungicide
 programmes to seasonal conditions, regardless of cultivar.
 • Canterbury trials demonstrated how a lighter touch approach can achieve a balance
 between disease control, resistance management, yield and gross margin.
 • Further trial data is needed to support lighter touch approaches in South Otago and
 Southland.

Wheat cultivar selection – South Otago/Southland season overview
In the 2020-21 season, for the second year in a row, there was above average rainfall through late
winter and into mid-spring. This resulted in challenges getting fungicide applications on at GS 32 and
increased Septoria tritici blotch (STB) disease pressure in the early part of the season. However, dry
conditions through November and December ensured disease only progressed to moderate levels in
the FAR fungicide trial at Clinton.
In addition to STB, conditions in some areas were conducive to the development of ear blight
complex. This complex is a combination of Fusarium and Microdochium species, and development is
favoured by dry winter conditions which build up inoculum, and then by wet conditions around
flowering and again in the weeks prior to harvest that result in disease expression.
Average yields were recorded in Southland trials with temperatures near average, and solar
radiation through grain fill around 12% higher than the previous season.

Cultivar selection can mitigate crop losses from disease
In recent years, nil fungicide replicates were included in the Cultivar Performance Trials at Chertsey,
Methven and Temuka (Figure 1). Despite low to moderate disease pressure, yield loss in the nil
fungicide treatments ranged from 1.7 t/ha for cv. Firelight (14% yield loss) to 5.1 t/ha for cv. Starfire
(46% yield loss) compared to the cultivars with a fungicide programme (Figure 1). The more
susceptible cultivars suffered greater yield loss than the more resistant ones, and consequently,
their response to fungicide was greater. We hope to include a nil disease replicate to the Balfour trial
in the 2022-23 season.

 7

14.0

 12.0

 10.0

 8.0
 Yield (t/ha)

 6.0

 4.0

 2.0

 0.0

 Fungicide Nil Fungicide

Figure 1. Mean yield for irrigated wheat grown with or without a fungicide programme at Chertsey,
Methven and Temuka, 2020-21.
Clinton: new fungicide programmes
Establishment issues meant the planned cultivar by fungicide trial at Clinton was abandoned, so a
trial was established to investigate new fungicide programmes. This trial used a single moderately
resistant cultivar that incorporated the original treatment list and some of the recently introduced
products from the last two seasons (Table 1).
In the trial, disease reached moderate levels for the untreated control in the trial. Fungicide
treatments achieved significant disease control compared to the untreated, although there were no
differences between individual fungicide programmes. This shows that under the low-moderate
pressure conditions experencied in the 2020-21 season, the selection of at least a moderately
resistant cultivar provided flexibility in programme choice, even when fungicide timings were not
optimal. Disease control results also showed how the new products Caley® Iblon® (Group 7 + 3
fungicides), QuestarTM (Group 21 fungicide) and Revystar® (Group 3 + 7 fungicides) could be
successfully incorporated into fungicide programmes. Whilst these new products provide growers
with more tools, care should be taken when using them as, with the exception of Group 21, they all
belong to existing fungicide groups. Group 3 fungicides (triazoles) are at a medium risk of resistance
development, and Groups 7 and 21 (SDHIs and QiIs) have a medium-high risk of resistance
development.

 8

Despite good levels of disease control, there was no yield response to fungicide, with more
programmes returning a net loss on fungicide spend. Trials in 2021-22 will continue to quantify the
flexibility provided by cultivar selection.
Canterbury trials
The 2020-21 wheat cultivar by fungicide trials at Chertsey continued to show disease control could
be achieved largely by selection of a more resistant cultivar. Average yield losses with irrigation were
0.6 t/ha (5%) for the mostly resistant cv. Firelight, compared with 4.1 t/ha (32%) for cv. Graham
(moderately resistant) and 4.7 t/ha (39%) for cv. Starfire (moderately resistant – moderately
susceptible), if the crop did not have fungicide applied (Table 2). Average yield losses without
fungicide were 0.4 t/ha (5%) for cv. Firelight, 1.4 t/ha (17%) for cv. Graham and 1.6 t/ha (21%) for cv.
Starfire under dryland conditions (Table 3).
Cultivar selection can provide flexibility in fungicide programmes in Canterbury
Under low disease pressure conditions, cultivar selection influenced flexibility in fungicide
programme choice under both irrigated and dryland conditions. Under irrigated conditions, for all
three cultivars, reduced input and flag leaf “straddle” programmes achieved similar yields to 4-spray
programmes. However, revenue-cost and gross margin analysis showed the economic return for the
untreated crop was equal to those from treatments receiving fungicides for cv. Firelight.
There was an economic return on fungicide spend for cultivars Graham and Starfire, but no
difference between fungicide programmes, suggesting that under trial conditions, reduced input
programmes represented the greatest balance between disease control, yield, financial return and
resistance management.
Under dryland conditions, cv. Firelight demonstrated the greatest flexibility; the gross margin for the
untreated crop was equal to fungicide treated crops. Economic returns for cv. Graham were similar
to the irrigated trial, with a return on fungicide spend over the untreated, but no difference between
the treatments themselves. For the more susceptible cv. Starfire, revenue-cost and gross margin
analysis showed it was possible to underspend on fungicide.
The lack of return on investment on some fungicide programmes raises the question of risk, and
demonstrates the importance of tailoring fungicide programmes to seasonal conditions, regardless
of cultivar. Overall, these trials were also able to demonstrate how a lighter touch approach could be
achieved without compromising profitability.

 9

Table 1. Disease severity, yield and margin-over-chemical cost ($/ha) for autumn sown wheat cv. Graham under dryland conditions at Clinton in 2020-21, following
 application of different fungicide programmes. Wheat price $390/t (Source: NZX Grain & Feed Insight).
 Growth Stage (GS), application date and fungicide treatment (L/ha)

 13.10.20 4.11.20 19.11.20 26.11.20 1.12.20 22.12.20 %LAA1 Yield MoC2
 GS30-31 GS32 GS33-37 GS39 GS45 GS65 by STB (t/ha) ($/ha)
 Nil - - - - - 27.3 9.7 *
 - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - - 12.8 10.2 8.7
 - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - Opus® 0.75 + Comet® 0.4 9.3 10.0 -126
 - Kestrel® 1.0 - - Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 16.6 9.9 -161
 - - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 11.5 9.9 -144
 Opus® 1.0 Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - Opus® 0.75 + Comet® 0.4 15.0 10.3 -23
 TM 5.5 9.8 -280
 Questar 2.0 + Kesterel® 1.0 Adexar® 1.25 + Opus® 0.15 Opus® 0.75 + Comet® 0.4
 TM 6.3 10.3 -66
 Kestrel® 1.0 Questar 2.0 + Kesterel® 1.0 Opus® 0.75 + Comet® 0.4
 Kestrel® 1.0 Adexar® 1.25 + Opus® 0.15 Opus® 0.75 + Comet® 0.4 9.5 10.3 17
 TM
 Kestrel® 1.0 Elatus Plus 0.75 + Opus® 0.75 Opus® 0.75 + Comet® 0.4 10.6 10.2 -49
 Kestrel® 1.0 Revystar® 1.5 Opus® 0.75 + Comet® 0.4 11.1 9.6 -310
 Kestrel® 1.0 Caley® Iblon® 1.5 Opus® 0.75 + Comet® 0.4 7.0 9.8 -240
 Mean 11.9 10.0 -125
 P value 0.006 0.3 0.2
 LSD (p=0.05) 9.1 0.6 252
 CV (%) 3.5
 Note: Yellow indicated the treatments that were amongst those that produced the greatest seed yield
 Adexar® (a.i. 62.5 g/L fluxapyroxad and 62.5 g/L epoxiconazole, Group 7 and 3 fungicides); Caley® Iblon® (a.i. isoflucpyram 50 g/L and prothioconazole 100 g/L, Group 7 and 3
 fungicides); Comet® (a.i. 250 g/L picoxystrobin, Group 11 fungicide); ElatusTM Plus (a.i. benzovindiflupyr 100 g/L, Group 7 fungicide); Kestrel® (a.i. 160 g/L prothioconazole + 80 g/L
 tebuconazole, Group 3 fungicide); Opus® (125 g/L epoxiconazole, Group 3 fungicide); Prosaro® (a.i, 125 g/L prothioconazole + 125 g/L tebuconazole, Group 3 fungicide); QuestarTM
 (a.i. fenpicoxamid 100 g/L, Group 21 fungicide); Revystar® a.i. (mefenitrifluconazole 100 g/L and fluxapyroxad 50 g/L, Group 3 and 7 fungicide) . 1LAA (%) – percent leaf area affected
 by STB and leaf rust. Disease was assessed on the top three leaves at GS 75-80; 2MoC ($/ha) – margin over fungicide cost

10

Table 2. Disease severity, yield, revenue – fungicide cost ($/ha) and gross margin ($/ha) for autumn sown wheat cultivars with different disease resistance ratings*,
 under irrigated conditions at Chertsey in 2020-21, following application of different fungicide programmes. Wheat price $390/t (Source: NZX Grain & Feed Insight).
 Growth Stage (GS), application date and fungicide treatment (L/ha)
 LAA LAA by Revenue Gross
 16.9.20 13.10.20 23.10.20 2.11.20 10.11.20 23.11.20 by STB Rust Yield - cost Margin
 Cultivar GS 30-31 GS 32 GS 33-37 GS 39 GS 45 GS 65 (%)1 (%)1 (t/ha) ($/ha) ($/ha)
 Firelight Nil - - - - - 6.8 6.6 12.0 4515 2904
 Firelight - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - - 3.5 5.0 12.5 4550 2940
 Firelight - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - Opus® 0.75 + Comet® 0.4 3.4 5.0 12.5 4472 2862
 Firelight - Kestrel® 1.0 - - Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 2.7 4.0 12.7 4559 2949
 Firelight - - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 2.2 2.9 12.7 4556 2946
 Firelight Opus® 1.0 Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - Opus® 0.75 + Comet® 0.4 0.6 2.5 12.5 4446 2836
 Graham Nil - - - - - 32.1 39.9 8.7 3240 1630
 Graham - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - - 19.1 34.8 12.7 4607 2997
 Graham - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - Opus® 0.75 + Comet® 0.4 13.3 24.3 12.7 4566 2956
 Graham - Kestrel® 1.0 - - Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 16.2 23.3 12.8 4568 2958
 Graham - - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 9.4 15.0 12.6 4492 2882
 Graham Opus® 1.0 Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - Opus® 0.75 + Comet® 0.4 8.8 13.1 12.7 4500 2890
 Starfire Nil - - - - 42.1 77.5 7.2 2666 1056
 Starfire - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - - 28.3 36.8 11.7 4244 2634
 Starfire - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - Opus® 0.75 + Comet® 0.4 27.4 36.4 12.0 4291 2681
 Starfire - Kestrel® 1.0 - - Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 17.4 24.1 11.8 4206 2594
 Starfire - - Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 16.3 22.9 11.9 4247 2625
 Starfire Opus® 1.0 Kestrel® 1.0 - Adexar® 1.0 + Opus® 0.25 - Opus® 0.75 + Comet® 0.4 11.6 18.9 11.9 4204 2594
 Mean 14.5 21.8 11.9 4274 2663
 P value

Table 3. Disease severity, yield, revenue – fungicide cost ($/ha) and gross margin ($/ha) for autumn sown wheat cultivars with different disease resistance ratings*,
 under dryland conditions at Chertsey in 2020-21, following application of different fungicide programmes. Wheat price $390/t (Source: NZX Grain & Feed Insight).
 Growth Stage (GS), application date and fungicide treatment (L/ha)
 13.10.20 2.11.20 23.11.20 LAA by STB LAA by Leaf Rust Yield Revenue – cost Gross Margin
 Cultivar
 GS 32 GS 39 GS 65 (%)1 (%)1 (t/ha) ($/ha) ($/ha)
 Firelight - - - 2.7 8.8 8.1 3001 1926
 Firelight - Adexar® 1.0 + Opus® 0.25 - 2.6 7.8 8.3 3102 1926
 Firelight Kestrel® 1.0 Adexar® 1.0 + Opus® 0.25 - 2.5 6.9 8.3 3013 1847
 Firelight Kestrel® 1.0 Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 1.4 6.9 8.7 3257 1936
 Firelight - Adexar® 0.62 + Opus® 0.45 - 2.2 6.9 8.5 3153 2001
 Firelight Prosaro® 1.0 Adexar® 0.62 + Opus® 0.45 - 1.9 3.8 8.5 3153 1936
 Graham - - - 6.0 53.0 6.8 2475 1400
 Graham - Adexar® 1.0 + Opus® 0.25 - 4.8 17.3 8.0 2950 1774
 Graham Kestrel® 1.0 Adexar® 1.0 + Opus® 0.25 - 3.3 16.9 8.4 3130 1874
 Graham Kestrel® 1.0 Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 3.1 16.2 8.5 3169 1848
 Graham - Adexar® 0.62 + Opus® 0.45 - 4.4 21.4 8.0 2952 1800
 Graham Prosaro® 1.0 Adexar® 0.62 + Opus® 0.45 - 5.0 16.6 8.2 3034 1817
 Starfire - - - 13.6 79.4 6.0 2201 1126
 Starfire - Adexar® 1.0 + Opus® 0.25 - 5.9 37.9 7.2 2667 1491
 Starfire Kestrel® 1.0 Adexar® 1.0 + Opus® 0.25 - 4.5 21.4 7.9 2921 1665
 Starfire Kestrel® 1.0 Adexar® 1.0 + Opus® 0.25 Opus® 0.75 + Comet® 0.4 4.7 20.3 7.9 2951 1630
 Starfire - Adexar® 0.62 + Opus® 0.45 - 5.7 23.2 7.1 2632 1480
 Starfire Prosaro® 1.0 Adexar® 0.62 + Opus® 0.45 - 4.2 14.3 7.7 2856 1639
 Mean 5.9 21.0 7.9 2923 1729
 P value

BYDV management
Jo Drummond (FAR)
Key points
 • BYDV field trials in mid Canterbury in the 2018-19 and 2019-20 seasons found that wheat
 crops did not suffer the same post-GS 31 yield losses as wheat plants tested under high
 aphid pressure in shade houses.
 • In 2020-21, a trial to compare BYDV incidence and severity in wheat crops grown from seed
 treated with a neonicotinoid (Group 4A insecticide) or from untreated seed, showed no
 significant differences in yield, thousand seed weight or bulk density between treatments.
 • Monitoring of aphids and beneficial insects and local weather conditions in the trial
 identified a potential BYDV risk period between GS 21 – 31.
 • Despite this risk period, few visual BYDV symptoms were observed post-flowering in the trial
 and no BYDV-PAV (the common virulent strain) was detected in randomly collected leaf
 samples following laboratory testing.
 • These data suggest that the threshold for BYDV disease expression was likely not reached in
 the trial between GS 21 and GS 31, regardless of seed treatment, possibly because beneficial
 insect populations were managing pest populations.
 • More trials are needed to understand:
 o seasonal variation in aphid pressure
 o potential risks should access to neonicotinoid seed treatments be removed.
Aphid pressure in field trials shows no impact on wheat post GS 31
Field trials in mid Canterbury in the 2018-19 and 2019-20 seasons found that wheat crops did not
suffer the yield losses observed post GS 31 in wheat plants tested under high aphid pressure in
shade houses. The lack of any yield loss in the trials was thought to be a result of lower aphid and
BYDV pressure in the field than in the shade houses.
Although no trapping data was collected to confirm low aphid and BYDV pressure in the field, crops
grown from insecticide-treated seed and without further insecticide applications produced yields
similar to those treated with foliar insecticides up to GS 31 or GS 39. This provided further evidence
that aphid pressure in the field was relatively low in comparison to that experienced in the shade
houses.
Can we manage aphid pressure without neonicotinoids?
The main seed treatment insecticides used for protection against BYDV vectoring aphids belong to
the neonicotinoid group (Group 4A insecticide) and include the active ingredients clothianidin and
imidacloprid. Neonicotinoids have been banned in Europe and are under review in New Zealand, so
cannot be relied upon as part of long-term BYDV management strategies.
The field trials in mid-Canterbury in the 2018-19 and 2019-20 seasons did not compare BYDV in
crops grown from seed treated with an insecticide with those produced from untreated seed. To
address the question of managing wheat crops without the use of neonicotinoid treated seed, in the
2020-21 season a replicated weigh-bin trial was established at Pleasant Point with insecticide-
treated (Poncho® a.i. clothianidin, Group 4A insecticide) and untreated seed. No foliar insecticides
were applied to the trial or surrounding crop.

 13

Monitoring of insect populations found fewer aphids than at either of the 2018-19 and 2019-20 trial
sites, however, beneficial insect numbers were similar (Figure 2). Aphid and beneficial insect
numbers dropped in late June but spiked again in July, meaning the crop, which had reached
tillering, was potentially exposed to aphids vectoring BYDV between late-June and late-July. Aphid
numbers remained low from late-July until late-October, by which time the crop was past GS 31. A
low, but steady beneficial insect population was observed through winter, with population increases
in early October and again in late October, which were in line with aphid population increases.

 2500 Risk period ? 25

 Aphid and beneficial insect numbers
 2000 20
 Degree weeks above 5.8°C

 Sowing GS21 GS31 GS39
 1500 15

 1000 10

 500 5

 0 0

 Degree weeks Aphids 2020 Beneficials 2020

Figure 2. Degree weeks above 5.8°C and aphid and beneficial insect populations between sowing
and two weeks post GS 39 for autumn sown milling wheat cv. Duchess sown as bare or insecticide
treated seed, under dryland conditions at Pleasant Point, 2020-21.
Visual assessment of BYDV symptoms post-flowering (yellow/red discolouration, plant stunting)
identified low disease levels across the crop (Table 3), which was confirmed by ELISA diagnostic
testing of BYDV-PAV (common virulent strain). Nevertheless, there were no significant yield,
thousand seed weight or bulk density differences between bare and insecticide seed treatments
(Table 3). This suggests that any risk of BYDV infection between GS 21 – 31 was likely reduced in the
trial by respective aphid and beneficial insect populations, even though a higher ratio between aphid
and beneficial insects in late-July (18:8), may have triggered an insecticide application.
These data underline the need for continued monitoring of local weather conditions and insect
ratios, as aphid pressure and BYDV development is seasonal. Future work will continue to investigate
whether insect and degree week modelling can allow growers to mitigate risk based on conditions at
the paddock level. It will also include bare seed as a treatment, and there is scope to include
biopesticides as an alternative to neonicotinoid seed treatments.

 14

Table 3. BYDV severity, BYDV-PAV incidence, yield and quality for autumn sown milling wheat cv.
Duchess sown as bare seed or treated seed under dryland conditions at Pleasant Point in 2020-21.
 Treatment BYDV BYDV-PAV Yield TSW Screenings Test
 severity* Incidence** (t/ha) (g) >2 mm Weight
 (%) (%) (%) (kg/hL)
 Poncho® 0.9 0 8.9 38.6 1.8 63.2
 Bare seed 0.8 0 8.5 38.3 1.5 61.7
 Mean 0.85 0 8.7 38.5 1.7 62.5
 P value 0.1 0.4 0.2 0.3
 LSD (p=0.05) 0.5 1.2 0.6 4.3
 CV (%) 2.5
Note. Poncho® (a.i. clothianidin 600 g/L, Group 4A insecticide) * Visual assessment of 1m2 quadrats,
** incidence determined by ELISA (Enzyme Linked Immunosorbent Assay) by Plant Diagnostics Ltd.
TSW: thousand seed weight.

 15

Ramularia leaf spot management in barley
Jo Drummond (FAR)
Key points
 • Right fungicide mixture + right timing = maximise yield + economic return + reduced disease
 severity + product stewardship.
 • The highest yields and profits (Margin-over-cost) for autumn sown barley, cultivar Surge,
 under moderate disease pressure conditions were achieved when fungicides were applied at
 GS 31 and GS 39 or at GS 31 and GS 49; however, Ramularia leaf spot (RLS) severity was
 lowest when fungicides were applied at GS 31 and GS 39.
 • There was no financial benefit to applying a GS 59 fungicide, despite the shorter application
 window between GS 31 and GS 39 applications.
 • Current results indicate some reduced efficacy of solo Group 3 (demethylase inhibitor –
 DMI) and Group 7 (succinate dehydrogenase inhibitor – SDHI) fungicides in the field.
 • Using a mixture of Proline® (a.i. prothioconazole, Group 3 fungicide) and Phoenix® (a.i.
 folpet, Group M4 fungicide) at both application timings was profitable and provided a strong
 fungicide resistance management strategy.
 • The addition of Acanto® (a.i. picoxystrobin, Group 11 fungicide) or Seguris Flexi® (a.i.
 isopyrazam, Group 7 fungicide) provided an effective mixing partner for managing leaf rust.
 • Promising disease control, yield and economic returns were achieved by the new product
 Revystar® (a.i. mefentrifluconazole + fluxapyroxad, Group 3 + Group 7 fungicide), however
 this product should be carefully stewarded to ensure its continued use.
 • Seasonal variation should dictate fungicide programme choice and fungicide timing.
In addition to isolate testing, which indicated that 100% of SdhC isolates are insensitive to SDHI
(Group 7 fungicides), Plant and Food Research surveyed farm-saved seed which had been collected
from across New Zealand and included many different cultivars and sowing dates (Figure 2). Samples
were tested for Ramularia DNA and compared to historical samples dating back to 1961. Testing of
27 samples identified that all were positive for Ramularia, albeit sometimes in very small quantities.
Despite small quantities, any detection above 5 pg/100 mg seed constitutes a risk (Soonie Chng, pers
comm). None of the historical samples tested positive for Ramularia.
 DNA presence

 Figure 2. Dot histograms for each cultivar of estimated Ramularia DNA quantity (pg Rcc / 100 mg
 seed). Plant and Food Research 2020.

 16

In recent seasons, fungicide trials have been set up in autumn barley crops at Geraldine, South
Canterbury. High disease pressure conditions for Ramularia include leaf surface wetness at GS 30/31
and the weeks following head emergence. In 2020-21, rainfall was low during stem extension, but
high following head emergence, so under these moderate disease pressure conditions, RLS
developed to reach high levels on the top three leaves in the crop by the end of grain fill; resulting in
a yield losses of up to 23%. The average yield loss of 18% was similar to 2018-19 and 2019-20 trials.
Disease severity and its impact on yield appears to be closely linked to the timing of symptom
development, where the earlier symptoms appear, the greater the yield loss. This will vary
seasonally so fungicide choice should be dictated by disease pressure and crop stress. In recent
years, RLS developed during or post grain fill, so its impact on yield was minimal. There also appears
to be a point of no return, after which RLS develops to a maximum level, regardless of fungicide
programme.
The average yield in the 2020-21 autumn sown barley trial was 11.5 t/ha and the untreated control
produced a yield of 9.6 t/ha (Table 4). While Proline® (a.i. prothioconazole, Group 3 fungicide) and
Seguris Flexi® (a.i. isopyrazam, Group 7 fungicide) applied alone reduced RLS compared to the
untreated control, better disease control was achieved when these products were applied in
mixtures with other fungicide groups. This further confirms that solo Group 7 (succinate
dehydrogenase inhibitor - SDHI) and Group 3 (demethylase inhibitor - DMI) fungicides are struggling
to control RLS in the field. Yields and economic returns, measured as margin-over-fungicide cost
(MoC) for these treatments, applied solo, were lower than when applied as part of a mix with other
fungicide groups.
Disease assessment data showed the multi-site fungicide Phoenix® (a.i. folpet, Group M4 fungicide)
gave good control of Ramularia when used in a mix with Proline® (a.i. prothioconazole, Group 3
fungicide) and additional rust protection such as Seguris Flexi® (a.i. isopyrazam, Group 7 fungicide)
or Acanto® (a.i. picoxystrobin, Group 11 fungicide). These data also show how timing of application
is important, with reduced disease severity and increased yield when the applications were made at
GS 31 and GS 39 compared with GS 31 and GS 49. However, MoC for these treatments were the
same. There was also no financial benefit to applying a GS 59 fungicide, despite the shorter window
between GS 31 and GS 39 applications. Promising disease control, yield and economic returns were
achieved by the new product Revystar® (a.i. mefentrifluconazole + fluxapyroxad, Group 3 + Group 7
fungicide), however this product should be carefully stewarded to ensure its continued use.

 17

Table 4. Ramularia leaf spot (RLS), grain yield at 14% moisture and economic margins following fungicide treatments on autumn sown barley at Geraldine, cv. Cassia in
 2019-20 and cv. Surge in 2020-21.

 Fungicide treatment (L/ha) and growth stage (GS) 2019-20 2020-21

 % LAA Yield MoC2 % LAA Yield MoC2
 GS31 GS39 GS49 GS59
 by RLS1 (t/ha) ($/ha) by RLS1 (t/ha) ($/ha)
 Nil Nil 45 8.5 0 85 9.6 0
 Proline® 0.4 Proline® 0.4 27 9.2 84 87 10.4 183
 Seguris Flexi® 0.6* Seguris Flexi® 0.6* 26 9.7 219 85 11.2 480
 Proline® 0.4 + Seguris Flexi® 0.6 Proline® 0.4 + Seguris Flexi® 0.6 14 9.8 184 68 11.6 553
 Proline® 0.4 + Phoenix® 1.5 Proline® 0.4 + Phoenix® 1.5 6 9.9 255 44 11.7 656
 Proline® 0.4 + Seguris Flexi® 0.6 Proline® 0.4 + Seguris Flexi® 0.6
 9 9.5 15 44 11.9 619
 + Phoenix® 1.5 + Phoenix® 1.5
 Proline® 0.4 + Acanto® 0.25 + Proline® 0.4 + Seguris Flexi® 0.6
 6 10.3 319 63 11.8 610
 Phoenix ®1.5 + Phoenix® 1.5
 Proline® 0.4 + Acanto® 0.25 + Proline® 0.4 + Seguris Flexi®
 6 9.5 64 14 12.2 759
 Phoenix® 1.5 0.6 + Phoenix® 1.5
 Proline® 0.4 + Acanto® 0.25 + Proline® 0.4 + Seguris Flexi® Proline® 0.2 + Seguris
 5 10.2 228 10 12.1 668
 Phoenix® 1.5 0.6 + Phoenix® 1.5 Flexi® 0.3
 Revystar® 1.5 Revystar® 1.5 - - - 15 12.5 807
 Mean 16.9 9.6 171 52 11.5 667
 P value

Cereal nitrogen use efficiency
Turi McFarlane (FAR)
Key points
 • Nitrogen is a key input in cereals; efficient management has multiple economic and
 environmental benefits.
 • Nitrogen use efficiency (NUE) can have multiple definitions.
 • Simple NUE indicators show good correlations with more complicated NUE measures in
 wheat systems.
Background
Nitrogen (N) is required in a cereal system to maximise yield potential, but this reward needs to be
balanced against the economic risk of overspending on fertiliser (reducing profit) and the
environmental risk of N losses to the atmosphere and water.
This balancing act provides an incentive to maximise nitrogen use efficiency. Nitrogen use efficiency
(NUE) is an indicator of how well your system is using nitrogen. Any discussion about NUE needs a
consistent and quantifiable definition of the term, as researchers have thought up multiple ways of
defining it. Table 1 lists the definitions that are the most applicable to arable systems.
The objective of this work
FAR’s NUE work aims to develop and promote a nitrogen use efficiency indicator for cereals that
meets the following criteria:
 1. Simple
 2. Uses readily available information
 3. Can inform future N management decisions
To achieve this, we are researching how simple Nitrogen Use Efficiency (NUE) indicators such as
Partial Factor Productivity (PFP) and Partial Nitrogen Balance (PNB) compare with indicators that are
more difficult to get all the data for on-farm. By correlating these simple indicators with more
complicated measures we can provide guidance on the next steps to improve NUE.

 19

Table 1. Nitrogen use efficiency terms, definitions and references.

 Term Acronym Calculation Reference

 Nitrogen use efficiency NUE Semenov et al. 2007
 
 =
 
 Where grain yield (kg grain/ha) and Na is nitrogen supply from soil, fertiliser and residue (kg N/ha). Units are kg grain/ kg N.

 Agronomic Nitrogen Use Singh et al. 1998 Chakwizira et al.
 aNUE
 Efficiency 2015 Ullah et al. 2019
 − 0
 =

 Where YieldNx is the yield from fertiliser applied treatments (kg grain/ha), YieldN0 is the yield from the no nitrogen control treatments (kg grain/ha) and
 
 Nx is the amount of fertiliser applied (kg/ha). Units are kg grain/kg fertiliser N.
 Evans et al. 2016 -
 Partial Nitrogen Balance PNB
 GRDC
 
 =
 
 Where NYield is the nitrogen in the grain removed (kg N/ha) and Nx is the amount of fertiliser applied (kg N/ha). Indicator is unitless.

 Partial Factor Productivity PFP Ullah et al. 2019
 
 =
 
 Where grain yield (kg grain/ha) and Nx is the amount of fertiliser applied (kg N/ha). Units are kg grain/kg fertiliser N

 Nitrogen surplus N Surplus Overseer®FM
 =

 Where N inputs = fertiliser, clover fixation, irrigation, atmospheric deposition (via rainfall), imported feed. N outputs = grain, milk, wool, meat,
 − 

 supplements, effluent. Units are N/ha.
 Nitrogen Conversion Wheeler et al. 2011
 NCE
 Efficiency Overseer®FM
 
 =

 Where Product N is the amount of N in product (kg N/ha), Nx is the amount of fertiliser applied (kg N/ha) NFix is the amount of N fixation from legumes
 + + 

 (kg N/ha) and NSup is the amount of N imported in supplements (kg N/ha). Indicator is unitless and is expressed as a percentage.

20

Outcomes
Initial work with historical data (Figures 1, 2, 3 and 4) has demonstrated that there is a good
relationship between agronomic NUE and simple NUE indicators (PFP and PNB). The rule of thumb is
that a higher PFP or PNB value indicates better agronomic NUE. A low PFP or PNB value means that
there is excess N in the system. Where excess N is identified, a deep soil mineral N test is
recommended; this will allow you to revise your N fertiliser input for the following crop.
Southland and South Otago data

 140 1.2
 PFP
 120 1
 PNB
 PFP (kg grain/kg fert N)

 100
 0.8
 80

 PNB
 0.6
 60
 0.4
 40

 20 0.2

 0 0
 0 10 20 30 40 50 60
 aNUE (kg additional grain/kg N)

Figure 1. Correlation between simple indicators (PFP and PNB) and agronomic NUE (aNUE) from N
response trials in autumn sown wheat held in Waiwera South in 2015.

South Canterbury North Otago data

 120 2.0
 PFP 1.8
 100 PNB 1.6
 PFP (kg grain/kg fert N)

 1.4
 80
 1.2
 PNB

 60 1.0
 0.8
 40
 0.6
 0.4
 20
 0.2
 0 0.0
 0 5 10 15 20 25 30 35
 aNUE (kg additional grain/kg N fertiliser)

Figure 2. Correlation between simple indicators (PFP and PNB) and agronomic NUE (aNUE) from N
response trials in autumn sown wheat held in Temuka in 2004 and St Andrews in 2007.

 21

Mid Canterbury data

 70 1.2
 PFP
 60 1
 PNB

 PFP (kg grain/kg fert N)
 50
 0.8
 40

 PNB
 0.6
 30
 0.4
 20

 10 0.2

 0 0
 0 5 10 15 20 25
 aNUE (kg additional grain/kg N fertiliser)

Figure 3. Correlation between simple indicators (PFP and PNB) and agronomic NUE (aNUE) from N
response trials in autumn sown wheat held at Chertsey in 2017.

Central Canterbury data

 180 3
 160 PNB
 2.5
 140 PFP
 PFP (kg grain/kg fert N)

 120 2
 100
 PNB

 1.5
 80
 60 1
 40
 0.5
 20
 0 0
 0 2 4 6 8 10 12 14
 aNUE (kg additional grain/kg N fertiliser)

Figure 4. Correlation between simple indicators (PFP and PNB) and agronomic NUE (aNUE) from N
response trials in autumn sown wheat held at Leeston in 2013.
Next steps:
 • Define the limitations of particular indicators and/or where they are most appropriate.
 • Test the usefulness of these NUE indicators with growers.
 • Develop a traffic light system of appropriate responses when a specific indicator value is
 generated.
 • Determine how these simple indicators relate to Overseer® Nitrogen Conversion Efficiency
 and N surplus values.

 22

Herbicide resistance survey and ryegrass management in cereals
Phil Rolston, Matilda Gunnarsson and Ben Harvey (FAR)
Key points
 • Herbicide resistance to several commonly used Group A and B herbicides was identified on
 17 of 26 farms in South Canterbury with ryegrass weeds in cereal crops.
 • Herbicide sequences, incorporating multiple modes of action, resulted in the greatest
 reduction in ryegrass populations in an autumn sown barley crop grown at a site
 contaminated with Italian ryegrass.
 • A spring wheat trial also demonstrated that a sequence of pre-emergence herbicides
 followed by a post emergence herbicide application is needed to control ryegrass.
 • Future work will examine the financial implications of using these strategies.
Background
FAR has completed three herbicide resistance surveys as part of the AgResearch-led MBIE funded
Herbicide Resistance Programme. The surveys sampled approximately 20% of arable growers in
Selwyn District (2019), South Canterbury (2020) and Southland (2021).
In South Canterbury, two fields from each of 37 randomly selected growers were surveyed. This
represented 23% of arable growers in the district. Samples were taken pre-harvest in the 2019-20
season. The fields selected were mostly crops of either wheat or barley. The weed species collected
were perennial and annual ryegrass, wild oats, Vulpia hairgrass and bromes.
Two field trials, one in winter barley and the other in spring wheat, compared single herbicide
applications with a sequence of pre-emergence and post emergence herbicides, incorporating
multiple modes of action, on the control of ryegrass and grain yield.
Results
South Canterbury survey shows widespread herbicide resistance in ryegrass
Of those tested, 59% of farms had Group A herbicide resistance (mostly to haloxyfop-P and
pinoxaden) and 53% of farms had Group B resistance (iodosulfuron or pyroxsulam).
Table 1. Ryegrass with herbicide resistance (HR), partial resistance (1-20% of plants died) or nil
resistance, from fields surveyed in South Canterbury in January, 2020.
 Number of Number of Partial HR
 Herbicide Herbicide active Nil
 fields fields with (1 -

Barley weed management trial
Increasing barley plant density at sowing from 150 to 225 plants/m2 increased competition, reducing
ryegrass seed head numbers by 23% and increasing barley yield. In a high-density ryegrass weed
situation, single herbicide options or mixes at one timing were not sufficient to control ryegrass
(Table 2).
Spring wheat weed management trial
Single timing applications were not able to achieve ryegrass control in spring wheat. Near complete
ryegrass control was achieved with a sequence of pre-emergence herbicides followed by a post
emergence herbicide (Table 3). The grain yields for all treatments averaged 8.4 t/ha. There was no
significant difference between treatments (data not shown).
Discussion
Ryegrass and brome grasses tend to emerge over a long period of time. Single timing herbicide
applications did not fully control ryegrasses that had emerged either early, or late, relative to the
treatment time. Herbicide sequences incorporating multiple modes of action provided good control.
It should be noted that the Firebird® label is for annual Poa and Vulpia hairgrass control and does
not make a claim for ryegrass control.
Most pre-emergence herbicides require soil moisture or about 10 mm of rainfall to be activated. In
dry autumn conditions this may not be achieved. However, most of these herbicides are stable and
will be activated once it rains. Delaying sowing or herbicides until rain is forecast is a risky strategy.
Preliminary industry trials in a low rainfall autumn in South Canterbury in 2020 demonstrated
excellent ryegrass control when Avadex® was pre-plant incorporated and followed by Sakura® pre-
emergence. When ryegrass pressure at the site was high, a follow-up post emergence herbicide
improved overall control.
Planned trials for 2021 will include Avadex®-Sakura® sequences and new ryegrass control herbicides
being released in Australian cereal systems. The financial implications of using these strategies will
also be examined.

 24

Table 2. Annual Ryegrass (cv. Winterstar) populations and winter barley (cv. Laureate) yield in a crop sown at two densities and treated with different herbicides in a trial
 contaminated with 50 kg/ha annual ryegrass at Chertsey, 2020-21.
 Pre-plant herbicide Barley Density Pre-emergence herbicide Early post-emergence herbicide Late post-emergence herbicide Ryegrass Barley
 Treatment
 (7 May) (plants/m2) (8 May) (1 ryegrass leaf) (4 ryegrass leaf) (heads/m2) (t/ha)
 1 150/m2 - 877 4.73
 2 150/m2 - Firebird (300 mL/ha) 670 5.91
 Stomp
 3 150/m2 - Firebird (300 mL/ha) 602 5.38
 (2.5 L/ha)
 4 150/m2 - Stomp (2.5 L/ha) + Firebird (300 mL/ha) 413 6.95
 2
 5 150/m Firebird (300 mL/ha) 503 6.00
 2
 6 150/m Sakura (125 g/ha) 250 8.46
 7 225/m2 - 474 6.26
 2
 8 225/m Firebird (300 mL/ha) 445 7.25
 2
 9 225/m Sakura (125 g/ha) 179 9.10
 Firebird (300 mL/ha) +
 10 225/m2 482 7.32
 Gardoprim (750 mL/ha)
 Firebird (300 mL/ha) +
 11 150/m2 431 6.42
 Gardoprim (750 mL/ha)
 Firebird (300 mL/ha) + diuron
 12 150/m2 568 6.69
 (1.3 L/ha)
 Sakura (125 g/ha) +
 13 150/m2 282 8.97
 Gardoprim (750 mL/ha)
 Sakura (125 g/ha) + diuron
 14 150/m2 295 9.38
 (1.3 kg/ha)
 15 150/m2 Firebird (300 mL/ha) + Gardoprim (750 mL/ha) Othello (1 L/ha) 41 10.52
 Firebird (300 mL/ha) + IPU (2
 16 150/m2 402 6.76
 L/ha)
 17 150/m2 Firebird (300 mL/ha) IPU (2 L/ha) 383 8.25
 LSD (p=0.05) 194 1.07
 P value

Table 3. Annual Ryegrass (cv. Winterstar) populations in spring wheat (cv. Discovery) with different herbicides in a trial contaminated with 30 kg/ha annual ryegrass sown at
 Kowhai Farm, Lincoln 2020/21.
 Pre-plant herbicide Pre-emergence herbicide Early post-emergence Late post-emergence Ryegrass (plants/m2) Ryegrass (heads/m2)
 Treatment
 (17 Sept) (24 Sept) herbicide (1 ryegrass leaf) (4 ryegrass leaf) (4 Nov) (4 Feb)
 1 - 280 110
 2 Stomp (2.5L/ha) - 116 33
 3 Sakura (125 g/ha) 152 41
 4 Firebird (500 mL/ha) 204 91
 Stomp (2.5 L/ha) + Sakura
 5 168 42
 (125 g/ha)
 6 Sakura (125 g/ha) Rexade (100 g/ha + 0.25% N_I surfactant) 92 1
 7 - Rexade (100 g/ha + 0.25% N_I surfactant) 64 6
 8 Sakura (125 g/ha) Othello (1 L/ha) 136 2
 Sakura (125 g/ha) +
 9 84 29
 Gardoprim (750 mL)
 Sakura (125 g/ha) + diuron
 10 96 27
 (1.3 kg/ha)
 Sakura 125 g/ha + diuron 1.3
 11 Othello (1 L/ha) 100 2
 kg/ha
 12 Sakura (125 g/ha) IPU (2L/ha) 196 14
 Sakura (125
 13 g/ha)+Gardoprim (750 Othello (1 L/ha) 76 1
 mL/ha)
 14 BAS 684 (650 mL/ha) Othello (1 L/ha) 108 1
 15 BAS 684 (650 mL/ha) 104 84
 LSD (p=0.05) 96 24
 P value 0.003

Grass grub
Sarah Mansfield (AgResearch) and Richard Chynoweth (FAR)
Key points
 • Organophosphate insecticides for grass grub control are disappearing from the New Zealand
 market due to changes in national and international regulations and consumer pressure.
 • Biological control utilising naturally occurring pathogens and/or predators of grass grub will
 become more important as chemical control options are removed.
 • Cultural control utilising strategic use of cultivation, cover crops and sacrificial crops are
 options for growers to consider.
Introduction
Approximately seven years ago the Environmental Protection Authority (EPA) set 3, 10 and 15 year
phase out periods for three important active ingredients used for chemical control of grass grub
(Costelytra giveni) in New Zealand. This meant that phorate was removed from the market in 2016-
17, while terbofus (Counter) and diazinon will be unavailable from 2023-24 and 2028-29,
respectively. While chlorpyrifos was retained, with additional controls imposed, its withdrawal from
use in the European Union will likely have flow on effects in New Zealand.
Growers now have a window of time to plan and test alternative strategies for long-term control of
grass grub. Currently the use of alternative insecticides (e.g. seed treatment Poncho® (a.i. 600 g/L
clothianidin)) and granular products (e.g. suSCon® Green (a.i. 100 g/kg Chlorpyrifos)) is common
practice.
New Zealand grass grub
New Zealand grass grub begin their lifecycle as eggs laid during November and December (Figure 1).
The larvae hatch about three weeks later and have three stages of larval growth, called instars.
Larvae develop into second instars from mid-January to late February, when they may move into the
top 6 cm of soil to feed on living roots. First and second instar larvae may feed solely on soil organic
matter. Third instars develop from February through until June and may be found as shallow as the
top 2-3 cm of the soil where they feed on living roots until developing enough fat to pupate. They
pupate during September/October at approximately 10 - 25 cm below the soil surface and emerge
as adults 4-6 weeks later. This one-year life cycle is typically found in arable crops and pastures, but
a two-year life cycle (Figure 1) is found in native habitats.
Natural controls
Pathogens are disease-causing organisms that can cause death or increase susceptibility to other
pathogens. Disease in grass grub populations may cause the population to collapse, particularly
when populations are high and food resources are low. In the North Island, protozoa (especially in
Taranaki) and milky disease bacteria (Bacillus popilliae) are mainly responsible for the collapse of
grass grub populations. In the South Island, Serratia entomophila (amber disease) is the dominant
pathogen. Species of fungi (Metarhizium sp. and Beauveria sp.) have been implicated in population
collapse in the Waikato region.
Recently, Serratia proteamaculans (AGR96X), a bacterium active against grass grub has been
identified from diseased C. giveni larvae. In laboratory bioassays, it killed 90-100% of grass grub
larvae within 5-12 days of ingestion. The rapid kill of larvae by AGR96X is more similar in speed to an
insecticide (Hurst et al. 2018).

 27

2020-21 field trials
In May 2020, two field trials were established to investigate the potential of AGR96X to protect
seedlings of barley, cultivar Planet (trial 1), and wheat, cultivar Discovery (trial 2), from attack by
larvae of the New Zealand grass grub. Previously the site had grown two years of ryegrass pasture
and during the summer prior to establishment, it was dryland with sparse cover maintained to
approximately 20 cm in height. Pre-planting assessments showed a larvae density of ~350/m2 with
variation in larval size. The trial area was irrigated, with 40 mm applied the day prior to direct drilling
with a double disc small plot drill into 8 x 1.35 m plots. Treatments (Table 1) were replicated five
times in a randomised complete block design.
Preliminary results
In trial 1, the plant population of barley was quickly reduced due to slug damage and grass grub
feeding. Poncho® based treatments provided final populations of ~86 plants/m2 while the untreated
was reduced to 28 plants/m2 (Table 1). Poncho® f.b. Grub Zero responded in a similar way to
Poncho® alone where larval feeding may have ceased at application.
In trial 2, plant losses from both slugs and grass grub were generally less severe than in trial 1.

 28

Table 1. Final plant population of wheat, cultivar Discovery, and barley, cultivar Planet, when sown
with a target plant population of 150 plants/m2 into a population of ~350 New Zealand grass grub
larvae/m2, following seven control options. Trial sown 13th May 2020 at the FAR Arable Research
Site, Chertsey.

 Final plant population/m2
 Treatment Product and rate
 Barley Wheat
 1 Nil 28 a 82
 2 SuSCon® Green (15 kg/ha) 75 ab 114
 3 Poncho® 85 c 114
 4 AGR96X (30 kg/ha) 61 bc 106
 5 Serratia entomophila (30 kg/ha) 53 bc 95
 6 AGR96X (15 kg/ha) + Serratia (15 kg/ha) 60 bc 101
 7 Poncho® f.b. Grub Zero - 16.7.20* 87 c 124
 LSD (p=0.05) 28.1 NS (29.8)
 P value 0.003 0.125
Note: Yellow indicated the treatments that were amongst those that produced highest plant
populations. *Date of application.
In trial 1, Poncho®, SuSCon® Green and AGR96X treatments produced the highest grain yields at 8.0,
7.8 and 7.1 t/ha, respectively (Table 2). Poncho® f.b. Grub Zero responded in a similar way to
Poncho® alone. In trial 2, the pattern repeated with Poncho®, SuSCon® Green and AGR96X
producing the highest grain yields. Grain yield was closely related to final plant population in both
trials (R2>0.9, data not shown).

Table 2. Grain yield of wheat, cultivar Discovery, and barley, cultivar Planet, with a target plant
population of 150 plants/m2, following seven treatments for the control of the New Zealand grass
grub, population ~350/m2, sown 13th May 2020 at the FAR Arable Research Site, Chertsey.

 Grain yield (t/ha)
 Treatment Product and rate
 Barley Wheat
 1 Nil 3.1 d 6.2 d
 2 SuSCon® Green (15 kg/ha) 7.8 ab 10.0 ab
 3 Poncho® 8.0 a 10.2 a
 4 AGR96X (30 kg/ha) 7.1 ab 9.0 abc
 5 Serratia entomophila (30 kg/ha) 5.0 c 7.8 c
 6 AGR96X + 15 kg/ha Serratia (15 kg/ha) 6.9 b 8.6 bc
 7 Poncho® f.b. Grub Zero - 16.7.20* 8.2 a 10.0 a
 LSD (p=0.05) 1.2 1.4
 P value

Notes

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 Christchurch 8441

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 Email: far@far.org.nz

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