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Stripe Rust: In Crop Management 2007 | AG1205 |
Grant Hollaway, DPI Horsham
Updated: June 2007
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With the favourable start to this growing season it is likely that stripe rust will be an important disease in Victoria in 2007.
Losses from stripe rust can be minimised, with active monitoring and timely fungicide applications if required.
This Information Note presents information on stripe rust identification and management strategies.
Stripe Rust Management: Summary
| 1. | Monitor all wheat crops weekly and know how to identify stripe rust.
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| 2. | In general prior to booting, crops should be sprayed before they reach 1% leaf area affected. (See ‘Disease monitoring’ below).
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| 3. | Stripe rust is better managed by applying sprays early in the epidemic.
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| 4. | When stripe rust is detected just prior to flag leaf emergence (GS39) and if the level is below 1% leaf area affected, delaying spraying to enable the flag leaf to fully expand can be of benefit.
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| 5. | After booting the need for fungicide sprays will depend on a number of factors including varietal resistance, level of stripe rust infection, crop yield potential and anticipated climatic conditions. |
What to Look For
Before spraying crops it is critical to ensure that it is stripe rust present in a crop and not some other problem. Stripe rust is easiest to identify in the morning. By looking at all leaves, especially the older leaves low in the canopy, look for yellow stripes of pustules. These pustules are raised above the leaf surface and can be easily wiped off onto a white cloth or tissue leaving a yellow stain. Figures 1 and 2 show severe stripe rust symptoms. Consult the guides listed at the end of this note for more information.
Disease Monitoring
All wheat crops should be monitored weekly for the presence of stripe rust. Once rust is found in a crop, collect 100 tillers from the crop by walking a diagonal or W pattern through the crop.
Count the total number of green fully expanded leaves and the number of these with any stripe rust on them. Stripe rust will be at 1% of leaf area when there are 30-40 infected leaves per 100 green leaves.
Watch for hot spots. When these are well developed and just before the disease becomes general in the crop, the average leaf area affected will be about 1%.
If and When to Spray
As most wheat varieties currently grown in Victoria are not completely resistant to stripe rust growers must be prepared to protect crops from loss using fungicide sprays during the season if required.
The requirement to apply foliar fungicides to a wheat crop will depend on a number of factors including:
- the reaction of the variety to stripe rust (Table 2),
- the stage of crop development when the stripe rust begins in the crop,
- the yield potential and expected value of the wheat,
- temperature during grain filling, and
- the cost of fungicide and its application.
Each crop should be considered on its own merit when deciding if fungicides are warranted, but growers must remember that early stripe rust infections (ie those present before flag leaf emergence) can cause the largest yield losses and they are best controlled by spraying soon after detection. If stripe rust is first detected later in the season (after ear emergence) large yield losses are much less likely and the application of fungicides often not warranted. | Figure 1. Stripe rust on the very susceptible variety H45 (photo courtesy C. Wellings).
Figure 2. Stripe rust on the MS- S variety Mitre (photo courtesy C. Wellings). |
As the potential loss from a given level of stripe rust decreases as the season progresses the control recommendation also changes with time. The following are recommendations based on the timing of the epidemic development.
Growth stage 31-37 (Stem elongation to before flag leaf)
Should stripe rust develop in a crop at this growth stage it should be sprayed before the leaf area affected reaches 1%. If the level is significantly below 1% leaf area affected (ie 0.1% leaf area affected), delaying chemical application by a few days can enable another leaf to be expanded and therefore be protected by the fungicide. Also when stripe rust is present at low levels (ie much less than 1% leaf area affected), delaying the first application until 3-4 weeks before flag leaf emergence, when a second application should occur, will give continuous protection of the crop. Spraying too soon will result in the need for 3 applications.
In general, however, at this growth stage it is best to apply fungicides earlier (ie at first detection in the crop) than later in the epidemic for best control, especially in crops rated as MS, S or VS. Early fungicide applications will help minimise the level of rust present to infect the newer leaves as they emerge.
Crops rated as Very Susceptible (VS) should be sprayed as soon as stripe rust is found in the district if a pre-sowing seed or fertiliser treatment has not been applied.
Growth stage 39-49 (flag leaf expanded to late booting)
This is the most important growth stage for a fungicide application. As the top two leaves contribute the most to yield it is critical to protect the flag leaf soon after emergence.
Regardless of variety, spraying should be done before stripe rust reaches 5% of leaf area affected on the flag. Once this level is reached, stripe rust becomes very difficult to control. In addition, because the disease will continue to develop for up to a week after spraying, considerable leaf area will be destroyed which in turn will make spraying uneconomic.
A fungicide application at this growth stage will give 3-5 weeks protection, depending on chemical and rate. At this time, in many varieties, adult plant resistance, combined with warming temperature, will slow the disease progress reducing the likely need of another application, however, crops should continue to be monitored and a decision made at that time.
In general crops that are rated as MS or worse to stripe rust will benefit from a fungicide application if stripe rust is present at low levels at GS39 (flag leaf emergence) and there is good yield potential (> 2.5 t/ha).
For crops rated MR-MS it is not as clear if a low level of stripe rust present at GS39 should be sprayed. The requirement for a foliar application will be greater in higher yielding crops and in wetter areas. This will vary from crop to crop.
In susceptible and very susceptible crops a low level of stripe rust present at this growth stage should be sprayed.
Growth stage 51-59 (heading)
In many regions if the level of stripe rust has been kept low a spray will not be required at this growth stage. Susceptible and very susceptible crops may need further protection along with those crops in cooler parts of Victoria.
Head infection can be common in many varieties grown in Victoria. The head becomes infected from spores from within the crop and blowing into the crop. If crops are sprayed before head emergence, the heads are not protected from spores blowing into the crop. Spraying after head emergence and before anthesis may reduce the level of head infection, but spraying after head infection does not. The best way to protect crops from head infection is to keep the rust under control within the canopy during the growing season.
Growth stage > 63 (flowering onwards)
Fungicide sprays are rarely warranted in late commencing epidemics. The exception is high-yield potential crops of susceptible varieties, where late sprays can give economic responses. In general late epidemics have minimal impact on grain yield.
Fungicide Sprays
Effective fungicides for controlling stripe rust are available see Information Note "Cereal Foliar Fungicides".
The fungicides available for stripe rust control both prevent infection and stop development of the fungus within the leaf. The protection from further infections begins as soon as the fungicide is applied. When taken up by the leaf, the fungicide can stop development of early infections but more established infection will continue to develop. This explains the often apparent increase in stripe rust for a few days after spraying. Control becomes apparent within a week of spraying and the period of protection is normally about four weeks.
Fungicides protect only the sprayed leaves. Systemic fungicides only move to the leaf tip, and are not moved around the plant. They do not move up the plant to leaves that grow after spraying.
In general, timeliness of application is more important than product choice although there are some differences in the efficacy of the foliar fungicides available.
Product Availability
Should there be high demand for foliar fungicides in Australia this year it is possible that supplies may become limited. Farmers should therefore avoid spraying in the absence of symptoms and ensure that all applications are timed for their best effect.
Varietal Responses for 2007
Victorian wheat varieties vary in their resistance/susceptibility to stripe rust. The more susceptible a variety the quicker that rust will develop and the greater the potential yield loss from stripe rust. For example the grain yield of several varieties in the presence of stripe rust at Horsham in 2005 is shown in Table 1. Figures 1 and 2 show the level of rust that developed on H45 (VS) and Mitre (MS-S) in 2003. The more susceptible a variety the greater the need for protection with fungicide sprays.
Since 2003 the Western Australian strain of stripe rust has been dominant. The ratings of many common varieties to this strain are shown in Table 2. For additional varieties refer to the "Cereal Disease Guide 2007".
New strain of stripe rust detected
Late in 2006 a new strain of stripe rust was detected in Victoria and southern New South Wales. This new strain resulted from a mutation in the ‘Western Australian’ strain that enabled it to overcome the resistance gene Yr 17, also known as the VPM resistance. Therefore, the level of resistance in varieties such as Camm, Pugsley, H46 and others, that were previously resistant has been downgraded. As the detection of this new strain was late in the season, there is limited data on how lines with this resistance gene will perform against the new rust strain. Table 2 gives some preliminary ratings to indicate how these varieties may perform against this new strain. If growing varieties with VPM resistance, it will be important to actively monitor crops with a view to applying foliar fungicides if necessary.
Adult plant resistance (APR) is a resistance that is widely used in Australian wheats. APR genes are often partial resistance genes that work by slowing down the rate of epidemic development. They do not stop the disease progress completely.
There are a number of APR genes used in commercial wheats. The relative effectiveness of APR genes can be influenced by factors such as:
- temperature (often working better at higher temperatures),
- crop nitrogen status (delayed onset in high nitrogen status crops),
- the variety that they are deployed in,
- the number of APR genes present (their effects are often additive), and
- the strains of stripe rust present.
Even though APR genes are widely used in Australian wheat varieties they are often not well understood.
Some APR genes may also be strain specific and therefore prone to being overcome by new strains of stripe rust. Other APR genes are regarded as “durable” and therefore less likely to be overcome.
In general, APR becomes effective at around ear emergence and works best if rust levels are not excessive in the crop at this time. In varieties that have APR as their only source of resistance it may be important to protect the earlier growth stages of the crop with seed or fertiliser treatments and/or fungicide sprays. In general, varieties rated as MS with effective APR will rarely lose all their flag leaf to disease, whereas varieties rated as S and VS are at risk of losing 100% of their leaf area to disease. It may be important to protect crops with foliar fungicides before the APR becomes active.
Table 1. Grain yield and yield loss in 8 wheat varieties with different reactions to stripe rust grown in the presence of high levels of stripe rust at Horsham in 2005.
| Variety | RatingA | Yield | Loss |
| H45 | VS | 0.6 t/ha | 70% |
| Krichauff | S | 0.9 t/ha | 66% |
| Diamondbird | MS-S | 3.1 t/ha | 30% |
| Chara | MS-S | 3.4 t/ha | 24% |
| Janz | MR-MS | 3.6 t/ha | 22% |
| Yitpi | MR-MS | 4.0 t/ha | 15% |
| Mira | MR | 4.3 t/ha | 10% |
| GBA Ruby | R | 4.6 t/ha | 6% |
| A R | = Resistant; | MR | = Moderately resistant; |
| MS | = Moderately susceptible; | S | = Susceptible; |
| VS | = Very susceptible |  | |
Table 2. Rating of wheat varieties to the Western Australian strain of stripe rust and provisional ratings to the new Yr17 virulent strain in varieties carrying this resistance
| Variety ReactionA |
| Cultivar | WA strain
(dominant strain) | Yr17 virulent WA strain (provisional)B |
| Annuello | MS | |
| Bolac | R | |
| Camm | MR | MS |
| Carinya | MR | MR-MS |
| Catalina | MR-MS | |
| Chara | MS-S | |
| Derrimut | R-MR | MR-MS |
| Diamondbird | MS-S | |
| Frame | MR-MS | |
| GBA Ruby | R | |
| H45 | VS | |
| H46 | MR-MS | VS |
| Janz | MR-MS | |
| Kellalac | MR-MS | |
| Meering | MS | |
| Mira | MR | |
| Mitre | MS-S | |
| Pugsley | MR | MS-S |
| Rosella | MR-MS | |
| Sentinel | R-MR | |
| Wylkatchem | MS-S | |
| Yitpi | MR-MS | |
| A R | = Resistant; | MR | = Moderately resistant; |
| MS | = Moderately susceptible; | S | = Susceptible; |
| VS | = Very susceptible | | |
B These provisional ratings are based on limited data and should be used as a guide only. Varieties without the Yr17 resistance (ie Annuello) are expected to perform the same to both strains of stripe rust.
Life Cycle
The stripe rust fungus requires living host plants on which to grow and produce spores. The main host is wheat, but it can infect some varieties of barley, triticale and some species of barley grass, and to a lesser extent brome grass and phalaris. Rust is not seed borne.
The fungus is dispersed as wind-blown spores which produce new infections. This cycle is repeated many times during the cropping season, causing rust to develop. Conditions suitable for rust development occur from April to December in Victoria and stripe rust can be expected in crops by September in most years.
The fungus requires temperatures of less than 18°C (optimum 6-12°C), with a minimum of three hours of leaf-wetness (for example, dew) for new infections to occur. Once an infection is established the fungus can survive short periods of temperatures as high as 40°C.
Sufficient rust survives summer on volunteer or self-sown plants to allow a new infection to develop the following season. Only one infected leaf per 30 ha of regrowth needs to survive the summer to produce severe rust infections.
Stripe rust can also infect the developing head reducing grain number and size. Chemical control of head infection is not considered to be effective.
More Information
Acknowledgement
Thanks to Wendy Bedggood for preparing this Information Note. The previous version was published in August 2005.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. | |
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