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Interactions between wheat varieties and fungicide applications in south-west Victoria

Chris Bluett1, Angela Clough1, Mick Keating1 and Gavin Kearney2

1 Department of Primary Industries, Ballarat, Victoria. www.dpi.vic.gov.au. Email Chris.Bluett@dpi.vic.gov.au, Angela.Clough@dpi.vic.gov.au, Mick.Keating@dpi.vic.gov.au
2
Consulting Biometrician, Hamilton, Victoria. Email gke29755@bigpond.net.au

Abstract

While the National Variety Trial (NVT) protocols dictate that wheat trials are managed without using fungicides, many wheat growers in south-west Victoria use fungicides as standard practice. To provide growers with independent information about variety performance with and without fungicides, a separate trial to assess the response to fungicide applications was sown adjacent to each of the three NVT wheat sites in the region in 2007. The dryland trials of 26 varieties and advanced breeding lines were sown in mid May using a three replicate, latinised design with two fungicide treatments (+/- fungicides). A regime of three applications of fungicide per trial, slightly higher than district practice, was used because of the broad range of maturities among the entries. Establishment and crop growth were good and grain yields were exceptionally high, up to 12t/ha at Hamilton, with a mean site yield of 7.8t/ha. Stripe rust and leaf rust were detected in each trial. Fungicide application had no significant effect on grain yields at Streatham, where there was low disease pressure. At Inverleigh, where disease pressure was also low, only four entries had significantly higher yields with applied fungicides. However, at Hamilton, where stripe rust was severe, including some head infection, 14 entries produced significantly higher yields (up to 60% higher) when sprayed with fungicide, and entry rankings changed markedly. These results highlight the benefits of providing variety information that assists all growers to choose appropriate varieties and prepare crop management plans, regardless of their preferred agronomic and disease control methods.

Key Words

Cultivars, rust, disease control, high rainfall, grain yield

Introduction

Many wheat growers in the high rainfall zones of southern Australia routinely apply fungicides to minimise yield losses from foliar diseases such as stripe rust and leaf rust. This is important when, as often happens, popular and well adapted cultivars lose disease resistance before equivalent or better replacements are available. Effective foliar fungicides are affordable and the knowledge of how to apply them effectively is increasing. Farmers are becoming aware that if they do not protect susceptible but otherwise suitable cultivars adequately, significant reductions in grain yield and financial return can occur.

The trials discussed in this paper were carried out in association with the three National Variety Trial (NVT) wheat sites in the High Rainfall Zone of south-west Victoria, which are carried out under protocols that do not allow the use of fungicides (GRDC 2007). However, many local wheat growers believe that to make informed variety choices it is vital they know how varieties perform when they are protected from rusts and other leaf diseases. The objective of the trials was to provide wheat growers with this information.

Method

Three trials were sown adjacent to the NVT trials at Hamilton, Streatham and Inverleigh in south-west Victoria. All were arranged in a Latinised design with three replicates, two fungicide treatments (+/-) and 26 varieties. The rainfall and details of the management of the experiments are given in Table 1. Fungicides were applied as an experimental treatment at three times, at growth stages 30-32, 37-45 and 57-65, which is one more than most grain growers would use, because of the broad range of maturities among the varieties. At the first two applications 200 mL/ha Nufarm Opus 125 (125 g/L epoxiconazole) was used, and 145 mL/ha Nufarm Hornet (500 g/L tebuconazole) was used at the last application. The trials at Hamilton and Inverleigh were sown on 1.7 m raised beds with 15 cm row spacing and 8 rows per plot. The Streatham trial was sown on flat land with the same plot width and row spacing. All trials were direct drilled into stubble with a cone seeder fitted with knife points and presswheels.

Table 1. Growing season rainfall and details of trial management of the three fungicide experiments conducted in south-west Victoria in the 2007-08 growing season

 

Site

 

Streatham

Inverleigh

Hamilton

April-November rainfall (mm)

478

415

470

Sowing date

21 May

24 May

15 May

Harvest date

28 December

2 January, 2008

8 January, 2008

Fertiliser (kg/ha)

100 diammonium phosphate

100 diammonium phosphate

100 diammonium phosphate

Herbicides
Presowing

2 L/ha Roundup Powermax (540 g/L glyphosate)

2 L/ha Roundup Powermax (540 g/L glyphosate)

2 L/ha Roundup Powermax (540 g/L glyphosate)

Post sowing

 

500 mL/ha Tigrex (25 g/L diflufenican
250 g/L MCPA

500 mL/ha Tigrex (25 g/L diflufenican)
250 g/L MCPA
15 g/ha Glean (75% chlorsulfuron)

Insecticides

100mL/ha Talstar (80 g/L bifenthrin)

100mL/ha Talstar (80 g/L bifenthrin)

100mL/ha Talstar (80 g/L bifenthrin)

Results

All three trials had coefficients of variation (cv%) under 15% as recommended in the NVT protocols. Grain yields of the varieties significantly differed at all three sites. Hamilton and Inverleigh also had significant differences for the fungicide treatments and had significant variety x fungicide interactions (Table 2).

Table 2. Site mean yields and significance of treatment differences and interactions

 

Streatham

Inverleigh

Hamilton

Site mean grain yield without fungicide (t/ha)

7.85

5.31

6.87

Site mean grain yield with fungicide (t/ha)

7.86

5.50

8.67

Variety

***

***

***

Fungicide

NS

**

***

Variety x Fungicide

NS

**

***

NS = not significant, ** P < 0.01, *** P < 0.001.

Streatham

Applying fungicides did not change grain yields at Streatham but there were significant yield differences among the varieties tested. Figure 1 shows that the CSIRO red grained winter crossbred CS95102.1 produced a significantly higher grain yield than any other variety in the trial. In fact, at all three sites, it out-yielded all other varieties by at least 1.1 t/ha. Chara was the highest yielding milling variety.

Inverleigh

Four of the 26 varieties at the Inverleigh site yielded significantly higher with fungicides than without fungicides (Table 3). The improved grain yield of Tennant and Mackellar w fungicides is of note as these varieties were considered resistant to stripe rust until quite recently. Leaf rust may partly account for their response to fungicides. The grain yield of LPB04-2403 declined in the presence of fungicides and this result cannot readily be explained. Regardless of the fungicide treatment, CS95102.1 yielded significantly higher than any other variety, followed by Tennant and Mackellar.

Table 3. Grain yields (t/ha) without and with fungicide applications at Inverleigh (LSD (P=0.05) = 0.559 t/ha)

Variety

No Fungicide

Fungicide

CS95102.1

7.66

8.27

Tennant

6.30

7.15

Mackellar

6.25

7.39

Chara

5.06

5.76

LPB04-2403

3.69

3.02

Figure 1. Grain yields Streatham variety yields (LSD(P=0.05) = 0.963 t/ha)

Hamilton

Hamilton was the highest yielding site and the site most affected by stripe rust. Figure 2. shows that CS95102.1 again produced a significantly higher grain yield than any other variety in the trial. The highest yielding white grained milling variety without fungicide was Sentinel while Chara and Sentinel were the equally highest yield milling varieties when fungicides were applied. The difference between the highest and lowest yielding varieties was more than five fold in the absence of fungicides. However, that gap was narrowed to just over two fold when fungicides were applied.

Figure 2. Hamilton variety yields, with and without fungicide treatment (LSD(P=0.05) = 1.3 t/ha). Error bars ate the standard error of the mean.

Discussion

Despite similar growing season rainfall, and being only a matter of approximately 100 km apart, the disease levels at each of the three sites were markedly different. The site with the highest rainfall had the lowest disease, demonstrating that factors such as rainfall distribution, temperature and humidity, are important determinants of disease levels. Farmers and agronomists need to be aware of when the weather is conducive to disease build up, and to be alert for the appearance and progress of diseases in their districts and in their crops. This is essential in order to formulate and carry out affordable and effective control strategies if required.

While the incidence and severity of rust were not scored in these trials, the adjacent NVT wheat trials, which had similar entry lists, were inspected and scored for stripe rust by a plant pathologist (G Hollaway 2007 pers. comm.). Stripe rust was the major disease observed at the sites, but there was a low level of leaf rust also present.

At Hamilton, which had the most disease, the stripe rust scores allocated to the entries in the NVT trial were all consistent with the published Australian disease ratings for the varieties (Wellings and Bariana 2007). Thus the variety Sentinel, rated as Resistant to Moderately Resistant (R-MR) for stripe rust, scored 2, in all three replicates of the NVT trial at Hamilton (where 1 is no disease and 9 severely infected), and the trial data in Figure 2 shows no significant yield difference with and without fungicides.

Conversely, the variety Yenda, rated Susceptible (S) for stripe rust, scored 7 in each replicate of the NVT trial at Hamilton, and the results show that the fungicide treatment raised its yield from 2 t/ha to 8 t/ha. Barham, which is rated Moderately Susceptible – Susceptible (MS-S), scored 6, 5 and 6 in the NVT trial, and its yield was increased by fungicides from 4t/ha to just over 8 t/ha.

There are some exceptions, however, which highlight a phenomenon that is often observed around the world. In crops and trials a regime of foliar fungicides has been known to increase grain yield in some varieties even when their disease resistance rating is reasonable or good, and when the noticeable level of foliar disease does not seem severe enough to cause that yield difference. For example, at Hamilton trials in 2007 Tennant yielded 6 t/ha untreated and over 10 t/ha with applied fungicides, yet its stripe rust rating is R and its scores in the adjacent NVT plots were 1, 1 and 2. At least one of the breeding lines also demonstrated this effect, although to a lesser degree. Continuing this set of trials over several years may provide some evidence about this phenomenon.

Conclusions

It is quite clear from these results that in 2007 farmers in some districts of south-west Victoria, including the Hamilton district, would have suffered quite serious economic losses from a decision to grow certain popular and otherwise suitable wheat cultivars, but failing to adequately control foliar diseases, especially stripe rust. Important cultivars in this category included the white grained varieties Kellalac and Chara, and the red winter varieties Mackellar and Tennant.

It is perfectly legitimate for a farm business to decide, as a matter of strategy or policy, not to invest in fungicide sprays for cereal crops, or to decide to use them only as a tool of last resort. However, as shown and discussed above it is also quite legitimate for farm businesses to decide that they are prepared to invest in them and use them on a regular basis, to control diseases if and when they occur or even to prevent their occurrence.

Fundamental to that decision is the ability of the farm business owner or manager to access the information required to choose cultivars to suit their preferred strategy. Such a choice must be able to be based on evidence of not only the resistance ratings of the available cultivars, derived from disease nurseries, but also upon evidence of their field performance when effective control measures are, or are not, applied.

References

GRDC (2007). National Variety Trials – the protocols. pp 56. http://www.grdc.com.au/uploads/documents/NVT_The_Protocols_22052007.pdf

Wellings C and Bariana H (2007). Responses of Australian Wheat Varieties to Stripe Rust. Cereal Rust Report Volume 5 (4), 1-3. University of Sydney, Plant Breeding Institute Cereal Rust Laboratory.

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