IMAG Home Page Summary of IMAG-GRDC Projects 2006 Nitrogen Trial 2006 Disc versus Tine Machine 2006 Precision Planting for Disease Management

2006 Precision Row Placement for Disease Control Trial


Summary
This trial confirmed previous work of NSW DPI that showed a reduction in the level of Crown Rot infection when wheat is planted between the stubble rows from the wheat crop grown the previous year. Plant establishment was also better under the same conditions, which could be due to less exposure to Crown Rot and other diseases and/or reduced physical impediment from the stubble.  Dividend® seed dressing also appeared to result in better crop establishment than the standard dressing, although this needs further work, particularly as the differences disappeared later in the growing season.

Trial Aims and Design

Crown rot (CR) caused by the fungus Fusarium pseudograminearum and Common root rot (CRR) caused by Bipolaris sorokiniana are a major constraint to Australian cereal production. Recent research conducted by NSW DPI has shown that the severity of CR and CRR is reduced by 60% and 25% respectively by precision placement of seedlings between rows of previous crop residues where the disease inoculum is high. Precision row placement using GPS guidance is likely to reduce CR and CRR levels in a no till farming system with additional benefits likely to be achieved if used in conjunction with rotations, grass weed control, varietal selection and nitrogen and fallow management.

This field trial aimed to demonstrate to growers the severity and incidence of CR and CRR where cereal crops are established back on previous cereal rows compared with established between previous rows. The trial also aimed to demonstrate to growers the capabilities and limitations of GPS equipment and controlled traffic systems in broadacre applications such as inter-row sowing.

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The site chosen for the trial was at "Almirica", owned by the Tink family, 25km east of Narromine.  Samples of stubbles and crowns were taken from a number of paddocks in order to identify the one with the highest disease pressure.

During the growing season, one metre strips were identified throughout the crop that were either entirely on last year's stubble rows, or in between two of last year's rows.  These were marked and will be sampled after harvest for disease load.  

A summary of the main aspects of the trial are as follows:

Paddock History: Wheat in 2005, Fallow in 2004 and wheat in 2003 and 2002.  Sampling of stubble indicated moderate-high levels of CR (20-50%) and low-moderate levels of CRR indicating a high disease pressure, hence suitable for the trial.
Date Sown: 3 August 2006
Variety: Sunstate at 60kg/ha.  Crown Rot - 3, Common Root Rot - 6, Stripe Rust - 7, Yellow Leaf Spot - 3, Root Lesion Nematode - 7; NSW DPI ratings.  In short, Sunstate is highly susceptible to CR, but tolerant of most other potential problems, making it an ideal choice to highlight CR differences.
Starter Fertiliser: 100kg/ha MAP.
Equipment Used: 12m NDF precision seeder with disc and tine delivery assemblies, pulled by a 285hp John Deere tractor.  MAP was placed using the tine, followed by the seed sown with the disc.  For more information, visit www.ndf.com.au.
In-Crop Spraying: 3 September - 75mL/ha Topik, 0.5L/100L Hasten at 70L/ha

The rainfall received at the site is as follows:

1 July 0.4 4 August 7.0 4 September 2.0 The total amount of rain received from 1 December 2005 to 30 June 2006 was 116mm.  Let's use some very broad assumptions, such as all fallow moisture was stored with 40% efficiency, and the crop converted available moisture at an efficiency of 15kg/mm.  Using the French-Schultz model and an evapo-transpiration loss of 110mm, we would expect the crop to fail^.  This corresponds to the fact no yield was obtained off the trial area.
3 July 0.8 6 August 0.2 7 September 4.0
10 July 0.2 25 August 4.0 8 September 0.2
15-19 July 26.2 26 August 0.2 10 September 3.0
23-26 July 11.6 31 August 3.0 19-22 October 1.2
TOTAL 39.2mm 14.4mm 10.4mm
TOTAL IN-CROP RAIN RECEIVED = 24.8mm
*  There has since been 1.2mm received in the period 19-22 October.
^ French-Schultz model: (in-crop rain + available fallow moisture - 110) x 15kg/ha/mm x 1,000 = expected yield in t/ha
                                      (23.6 + 155 x 40% - 100) x 15 x 1000 = negative number

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Results
As expected, with the high background levels of CR and CRR, there was a better establishment rate in the between-row treatment (Table 1).  This suggests that these diseases (and possibly others) associated with the residue of last years stubble may have reduced plant establishment. Alternatively, reduced plant establishment when establishing the crop directly on the previous cereal rows may occur from a physical constraint associated with the incorporation of stubble into the seed furrow e.g. reduced seed-soil contact.

Interestingly, there was also a seed treatment effect, with the Dividend® treatments having higher starting plant populations than those treated with Raxil® (Table 2).  However, when the combined effect of placement and treatment was examined (Table 3), there was not a significant difference between the Raxil® between-row and the Dividend® on-row, i.e. the seed treatment could not overcome the disadvantage of being placed on last years residue.  This indicates that the Dividend® may be providing protection against a disease (or diseases) that are not affected by stubble residue.  However, the least significant difference (LSD) for the placement x treatment analysis was 4.86, and the difference in the Raxil® between-row and the Dividend® on-row was 4.83.  Therefore, the effect is significant at 94% (but not 95%), indicating further investigation is warranted.

Around the same time as these counts were conducted, Mr. Jock Leys of Syngenta performed an in-field enzyme test to determine if there was any Pythium present in the trial area.  This test is a positive/negative test only (i.e. a level of inoculum is not determined), but it did indicate that Pythium was present at the trial site.  Given Dividend’s registration for Pythium at the rate used (2.6L/tonne seed), this may explain the above results, although the dry conditions at this time would inhibit Pythium activity.  

Table 1: Row effect Table 2: Treatment effect Table 3: Row and treatment effect
Row Placement Plants/metre Seed Treatment Plants/metre Raxil On 19.8 c
On 24.6 a Raxil 22.2 a Between 24.5 bc
Between 30.3 b Dividend 32.8 b Dividend On 29.3 ab
Between 36.2 a
Means with different letters (within the one table) are significantly different at the 95% level.

The site was sampled by Dr. Simpfendorfer and IMAG just prior to harvest and CR and CRR levels determined using plating techniques.  Further plant and tiller counts were performed when the samples were removed from the paddock for laboratory analysis.

Interestingly, the treatment effect recorded 30DAS did not carry through to harvest time (Table 4).  Whilst the Dividend® treatments were still higher at harvest, the difference was not significant.  The results for tillers per plant suggest the Dividend® between-row was the same as Raxil® between-row (but lower than the two on-row results), whereas all other results are the same.  It is difficult to draw any useful conclusions from these results.

Table 4:  Plant counts

Seed treatment

Row placement

Plant per metre

Tillers per plant

Raxil®

On

22.2

2.4 a

Between

22.7

2.1 ab

Dividend®

On

27.3

2.5 a

Between

26.3

1.8 b

LSD

 

ns

0.4
Means with different letters are significantly different at the 95% level.


Table 5:  Pathology results

Seed treatment

Row placement

% CR tillers

Brown height

CR Severity

% CR

% CRR

Raxil

On

46.5a

0.57 a

9.5 a

72 a

8

Raxil

Between

17.5b

0.23 b

1.8 b

25 b

13

Dividend

On

55.2a

0.68 a

12.7 a

79 a

4

Dividend

Between

23.7b

0.25 b

2.3 b

43 b

9

LSD

 

11.8

0.19

4.6

27

ns
Means with different letters are significantly different at the 95% level.

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The pathology results showed much clearer differences (Table 5). They clearly reflect the improved CR disease status of plants sown away from the previous year’s stubble and is irrespective of seed treatment.  The percentage of tillers with CR (both basal browning and detected when plated), browning height and CR severity were all significantly different for the placement effect, with no seed treatment effect being noticed.  The only comment that can be made regarding the treatment effect was that Raxil®, whether on- or between-row, had less CR than Dividend® in all measurements.  However, the variability in these measurements across the replicate sampling means that these seed treatment differences were not significant. This potentially corresponds to observations that tebuconazole (the active in Raxil®) does have some activity against Fusarium species. However, it is important to note that this was a minor trend only and did not approach statistical significance in any instances.

The inter-row sowing results confirm earlier work by NSW DPI and highlights the benefits of this technique on CR infection.  The incidence of CRR was quite low in across all treatment, which was the main reason the levels that were present were found to be non-significant. CRR is favoured by wet soil conditions which were very limited in the 2006 growing season at this trial site. This is why although pre-sow stubble testing indicated moderate levels of Bipolaris sorokinianai at the site very limited CRR infection was evident at harvest.

There did appear to be a visual effect between the seed treatments as well (Figure 1).  Participants at the field day held on 19 September 2006 noted with interest the difference between the two products.  The nature of crown rot infection at that stage (mid-tillering) meant no visual effects could be seen between the two row placement treatments.  Most participants indicated a desire to see further work done in this area and although not part of the original GRDC extension trial, IMAG will aim to investigate this further in the next cropping year where hopefully more favourable seasonal conditions will facilitate better evaluation of these disease management options.

Figure 1:  Dividend and Raxil treated seed at mid-tillering

Dividend and Raxil treated seed at mid-tillering
Dividend® Raxil®

Obviously, because the trial area was not sown using high-accuracy GPS in the previous (2005) season, there were no harvestable areas for on- and between-row comparison.  The laboratory work was all done on hand-picked locations.  Therefore there was no data to compare these two techniques (and was not an aim of the trial for that reason).

However, a small amount of grain was harvested off the trial area that enabled a comparison of the Dividend® and Raxil® seed treatments, independent of on- or between-row placement.  Due to the aforementioned dry seasonal conditions, yields were exceptionally low.  The two areas yielded almost the same, with an average yield of 320kg/ha and 324kg/ha for the Raxil® and Dividend® strips respectively.  Nothing can be drawn from such low and similar results.

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