Best Fungicide Options for Managing Disease in Wheat & Barley
With an outstanding start to the 2020 season and lots of early moisture, most crops are physiologically ahead compared to last year. We are beginning to see fugal disease.. creeping into our cereals despite the use of quality seed and fertiliser fungicide treatments.
Septoria Tritici Blotch in Wheat:
Off the back of a very wet start in 2019, there has been a strong trend in 2020 of early sowing with many growers choosing to grow popular winter wheat varieties and get them in the dirt by late march-early April. Most of the popular varieties are susceptible to Septoria Tritici Blotch (STB) and this early sowing has lifted disease pressure with increased early infection leading into winter. Septoria does not need a green bridge to survive over summer as it incubates on crop residue which allows it to spring up despite good summer weed control. The fruiting bodies (pseudothecia) which live on the stubble of previous years crops become windborne and can then travel over long distances and are the primary source of infection. The secondary source of infection is caused by short distance spread from spores called conidia which are produced on the infected leaves and are then splashed onto nearby leaves by raindrops. The disease needs long periods of leaf wetness to develop in the plant. There have been gene mutations in STB which are slowly making our Triazole (DMI) fungicides less effective against it, hence the need to combine different modes of action into products.
Figure 1. Typical Septoria Tritici blotch symptoms produced on young wheat leaf
Septoria Top Fungicide Options:
Radial – Commonly applied at the 500ml/ha rate in Sth West Vic ($17.3/ha) contains both a strobilurin and a triazole (epoxiconazole which is highly effective on STB) giving extended protectant activity and is a very strong option.
Soprano 500 – A new formulation of straight epoxiconazole used at 125ml/ha ($16.7/ha) which gives a robust rate of Epoxy that is systemic in the plant and is very effective on STB. A registration extension has given it a 3-week withholding period for cutting crops for stock feed.
Aviator Xpro – Is the first registered foliar fungicide in cereals in Australia containing an SDHI, giving us a different MOA to reduce the risk of resistance building up against in DMI and Strobilurin products. Commonly used around 500ml/ha rate in high disease pressure ($27.25/ha) it is costly but does a great job and protects our other chemistry from developing resistance from over exposure.
Septoria control Strategy:
Avoid Sowing wheat on wheat as Septoria survives on stubble. One year out of wheat is highly effective at reducing disease expression.
If sowing wheat on wheat make sure to get a good burn and do not sow too early.
Avoid sowing varieties with the lowest Septoria disease rating.
Spray a suitable fungicide (as indicated above) around GS31-33 (when the crop has between 1-3 detectable nodes in main stem). This will keep the disease inhibited before the canopy closes up and humidity and moisture within the canopy increase.
Figure 2. Cereal growth stage GS31. First node detected in the main stem
In years of good moisture heading into spring it is very important to apply a flag leaf GS37-39 fungicide in addition to the GS31 spray. GS37-39 is when the flag leaf becomes visible to fully unrolled. Depending on conditions, this spray can be critical as it will protect the top three leaves which are responsible for the majority of grain yield in wheat. Radial is a very popular choice for this growth stage.
Rotating Modes of Action:
Nick Poole (Managing director of FAR Australia) has been looking closely at Septoria and has determined it to be the most serious fungal disease of southern Australia. His work shows that DMI chemistry develops resistance slowly. We are highly reliant on DMI’s and so we must protect it by rotating it with other groups like those in Aviator Xpro and Radial which combine DMIs with other modes of action such as the strobilurin and SDHI’s. Full resistance to entire modes of action over in Europe is common and Nick is hoping that we can avoid the same fate in Australia. DMI’s develop resistance slowly where as strobilurin and SDHI groups are in a much higher risk category and so a strict rotation must be used to avoid resistance. He also supports only using fungicides where required and not over applying.
Stripe Rust in Wheat
According to Professor Robert Park of the university of Sydney, the first detection of stripe rust in wheat for 2020 has already been made near Dubbo in NSW. It was made on the 24th of June 2020. In the 40 years that stripe rust has been in Eastern Australia the average date that its been first detected in wheat is the 13th of July and so this year it has come a little earlier than normal. This first detection timing is important as it marks the onset of disease development and the earlier this happens in the crop cycle, the greater the epidemic potential.
This being said we should make sure that we closely monitor our crops as we can expect to see it soon. Detailed monitoring will be important for those varieties that are more susceptible to the new stripe rust strain such as Trojan. Generally, if we follow a good Septoria fungicide program with two fungicides then stripe rust is not going to be much of an issue.
Fungal Disease in Barley
The main foliar diseases of Barley continue to be Net blotch (both spot and net form) and Scald. The combination of improved seed treatments and new foliar sprays has given us good options to limit these diseases. Like in wheat, the GS31 timing for fungicides is critical for managing disease through the canopy. Options for improved seed treatments such as Systiva (SDHI) paired with a well timed GS31 foliar fungicide have been producing very clean crops. We must ensure that we protect the SDHI Mode of Action by not using a foliar fungicide containing an SDHI if Systiva has already been used on the seed.
Top Fungicide options:
Top Notch – This is a new fungicide that contains both a DMI and a Strobilurin component and is used around the 500ml/ha mark ($18.7/ha). Top Notch is a great option around growth stage GS31 to keep the canopy clean from disease. It is both a curative and a protectant giving good activity across the barley disease spectrum. Topnotch is the new benchmark for disease control in Barley.
Prosaro – Tried and tested product that has been very popular over the years and still getting very good performance. Made up of two strong DMI actives and is commonly used around the 230ml rate ($17.1/ha).
If you have any questions around fungicide use and control strategies, please do not hesitate to contact your local Western Ag Agronomist.
Article produced by - Lachlan Bullen, Western AG Ballarat/Derrinallum