Managing stripe rust
By Dr Scott Lane, Technical Manager
During the 2005 winter cropping season, stripe rust was widely detected throughout the wheat belt of Australia. Since it is expected to be a disease of concern for the upcoming 2006 winter crop, it's important for growers to have their stripe rust management plan in place before the season begins.
Background to the WA strain
The original stripe rust pathotype arrived in Eastern Australia during 1979 and since then many pathotypes have developed. One of the most damaging is the 'WA' pathotype, or Western Australia strain, that entered WA in 2002. The WA strain is highly virulent and is now the main pathotype present throughout the wheat belt.(1)
The WA strain is more damaging on many varieties than earlier strains of stripe rust and has set a new precedent in resistance ratings due to its virulence. This has resulted in varietal reaction scores of 1 to 3 units less than in previous years, reducing some varieties with moderate resistance (6 or 7 rating), to moderately susceptible (rating 4 or 5).(1)
The level of damage caused also depends on the susceptibility of the variety, how early the epidemic begins, the amount of stripe rust that develops, and the temperature during grain filling. Potential damage (yield loss) caused by stripe rust is provided in Table 1.
Table 1. Potential yield loss as a percentage for varieties of varying levels of resistance.
| Percentage yield loss (%) for varieties with varying levels of resistance | ||||
|---|---|---|---|---|
| Epidemic start | Susceptible (2) | Moderately susceptible (4) |
Moderately resistant (6) |
Resistant (7) |
| First node (GS31) |
85 | 75 | 55 | 25 |
| Flag leaf (GS39) |
75 | 45 | 15 | 5 |
| Mid boot (GS45) |
65 | 25 | 7 | 2 |
| Awn peep (GS49) |
50 | 10 | 3 | 1 |
| Mid-heading (GS55) |
40 | 5 | 2 | 0 |
| Mid-flowering (GS65) |
12 | 2 | 1 | 0 |
How does stripe rust survive?
For stripe rust to survive, it relies on having a live host to grow and produce spores with wheat being the principal host. However, some other cereals and grasses such as barley, triticale, barley grass and brome grass, can play a minor role in its survival.
The fungus reproduces by spores, with many generations occurring throughout the
cropping season. Stripe rust is spread by wind borne spores, which can travel
long distances and spread the disease to your neighbour's farm, to the next shire,
or even to another state.
Stripe rust development is favoured when certain conditions are satisfied. These
include:(3)
- Temperatures of less than 18°C (optimum 6-12 °C)
- Leaves are required to be wet for at least three hours for a new infection to occur
- Once the infection is established, stripe rust can survive short periods of temperatures as high as 40°C
- The fungus will survive during summer on volunteer cereals and provide inoculant for a new infection in the 2006 winter crop
- Only one infected leaf per 30 ha of regrowth needs to survive over summer to produce severe rust infections(3)
Resistance
Genetics and the inherent resistance that they produce are very important in the management of stripe rust. There are two types of resistance; 1) seedling resistance and 2) adult plant resistant (APR).
Combinations of genes providing APR have proven to provide the most effective resistance under Australian conditions. APR develops as the plant grows. It can start from stem elongation to heading(1) and works best if rust levels are not excessive in the crop at this time(3). The onset of APR is influenced by factors such as the environmental conditions and the nutrient status of the crop. In general terms, the longer the plants stay in the vegetative state, then the longer it takes for APR to develop. Therefore seed treatments are an important tool which can protect the plant until APR is able to protect the plant from stripe rust.
Stripe rust management
Management of stripe rust has a number of phases aimed at delaying the onset of the disease(3). To achieve this it is important to:
- Control/destroy the green bridge to delay the onset of the epidemic
- Understand the resistance status of your varieties and sow resistant varieties that meet your agronomic requirements
- Use seed treatments to protect your crop during its early development and prior to the onset of APR
- Monitor crops regularly so that the appropriate foliar fungicides can be applied, if required, later in the season
Fungicide options
Seed treatments are a convenient and important tool for managing stripe rust. The seed treatment is applied directly to seed and is readily taken up by the plant as it grows and develops, thereby providing immediate protection against air borne spores and delaying the onset of the disease until APR kicks-in.
Choice of seed treatments available are:
- Foliarflo-C® – Field experience has shown that this product provides suppression for about 8 weeks after sowing and delays the onset of the disease in the crop. Estimated cost $4/ha(4) plus application costs.
- Alphaflo® – At the high application rate gave good suppression for longer than Foliarflo in WA trials in 2003. It also has an additional benefit of being softer on the germinating seedling than Foliarflo. Estimated cost $9/ha(4) plus application costs.
- Maxiflo® – The active ingredient fluquinconazole is taken up more slowly than the other seed treatments and hence is able to provide the longest protection of all the seed treatments. Field experience has shown protection up to flag leaf emergence and longer in late sown crops. Estimated cost $20/ha(4) plus application costs.
In-furrow treatments (fertiliser-applied fungicides) are a potential option. However, they do not control smut or bunt, so a smuticide seed treatment for these diseases is still required.
The effectiveness of fertiliser-applied fungicides is dependent on fertiliser placement relative to the seed. Unlike fungicide seed treatments being applied directly to seed, fertiliser applied fungicides rely on plants coming into contact with the fungicide in the soil, and this can be influenced by environmental conditions which may affect the availability of fungicide to the plant. Therefore, anything that inhibits plant growth may also inhibit the plants ability to take up fertiliser-applied fungicides.
An additional advantage of seed treatments over in-furrow treatments is that with in-furrow treatments your fertiliser program becomes fixed because you must apply the correct rate of fungicide. Therefore you are not able to adjust the level of nutrition to meet your crop's requirements.
The length of protection provided by any fungicide, whether seed treatment or in-furrow, is dependent on product choice, rate of plant growth, amount of active ingredient available to the plant for uptake, level of disease, level of disease resistance, and seasonal conditions.
Footnotes
1. Murray, G et al (2005) NSW Department of Primary Industries - Stripe rust: Understanding the disease in wheat.
2. The Land, January 6, 2005.
3. Hollaway, G and Brown, J (2004). AG1148. Stripe rust Management: Update September 2004.
4. Cost estimates prepared assuming a sowing rate of 65 kg/ha.
