Now that seeding is completed, our attention has turned to post emergent radish and grass control and early fungicide applications.
The 2015 cropping season saw a large variation across the country in climatic and seasonal outcomes. Parts of south Australia and Victoria experienced below average rainfall where north WA and parts of NSW had above average years. One consistent factor was the large amount of 2015/16 Summer rainfall experienced across most growing regions. This lead to multiple germination’s of weeds and volunteers across the fallow period.
Growers are increasingly managing these germination events as soil moisture retention becomes a leading concern in an increasingly variable climate. The advantage of this summer weed management is the secondary (primary for some!) benefit of reducing the ‘green bridge’ that allows increased insect and fungal burdens to be carried into the following season.
In 2015, powdery mildew infections in wheat crops appeared for the first time in a decade across large swathes of the WA wheatbelt, with rusts and septoria’s experienced widely across the country. In some cases regions/varieties previously unaffected were experiencing pathogenic fungal incidences. As we move into the 2016 season, attention should be paid to the prevention of fungal infection in crops. Spores from most fungal pathogens are highly virile, hardy and can travel large distances to sites of infection. With this in mind, while summer weed management is generally improving, not everyone engages in this practice and roadways, pastures and un-managed fallows will still provide out-of-season hosts to most fungal pathogens.
With average to above average rainfall forecast for many growing regions, the high levels of infestation in 2015, and a solid summer green bridge, there is the potential for 2016 to be another above average fungal pressure season. A collaborative collection of trial data from the 2015 season by DAFWA, Imtrade Australia, Liebe Group and Landmark (Beard et al 2016) identified some key points for the management of powdery mildew in crops which is pertinent to most pathogens. It found the application of fungicides to pathogens that were present at low levels of incidence in the crop provided the best outcomes for control and yield. It also confirmed that only emerged plant tissue at the time of fungicide application is protected from pathogenic infection; new growth post-application is susceptible. So what does this mean for management?
- Fungicides work best as protectants, very few provide eradication.
- Regular scouting of crops is crucial to your decision making about fungicide application.
- Apply a fungicide when pressure is very low, but the pathogen is present.
- In combination with the above, if application has to be made prior to flag-1 or flag emergence, a follow-up spray may be necessary around 4 -6 weeks later to prevent infection of unprotected tissue.
In terms of post emergent fungicide choice, most trial work demonstrates any registered fungicide applied at a robust rate will provide results. The concern is that unlike weeds, which we generally manage herbicides well; the standard answer to fungicide is ‘what’s the cheapest option to do the job’.
Many farmers I have spoken to (not all!) are happy to continue using the cheapest option until they break it and then move onto the next option. Unfortunately this creates a huge problem. For example, in powdery mildew a gateway mutation in the pathogen must develop before triazole resistance mutations can develop in the target gene. The problem is, once this gateway is present, all actives in the family are equally prone to developing resistance.
In this example, if you continue to use tebuconazole spray on spray and eventually develop resistance, this means you actually have a gateway mutation AND a tebuconazole resistance mutation. Once that gateway mutation is present, rapid resistance to other triazole actives can develop rapidly. In recent work conducted by Curtin University, the triazole gateway mutation in powdery mildew has been discovered in an alarming number of samples in NSW and TAS (Cox et al, 2016). So what does this mean for management?
- Minimise pressure on actives by applying at appropriate timings as discussed above
- Rotate actives, preferably to a different mode of action, although rotating within groups is better than a single active
- Consider combining modes of action
- Use robust rates at all timings
Imtrade Australia understands the issues some traditional formulations of fungicides present when considering preventative/optimal timing spraying. Primarily the concern is that products cannot sit on a shelf from one season to another in readiness for an outbreak as they tend to fall out of suspension and become unusable. This has led to the purchasing of fungicide products once pressure is discovered/expected. The lead times on getting large volumes of product into a store and out to the farm is an issue. As discussed above, once a situation is identified, the best management practice is to spray as soon as possible. This is often delayed by waiting on stock to arrive, by which time the optimal window for control/prevention is well past.
Imtrade Australia has devised a solution to this problem, wherever possible, we supply our fungicidal products as high-loading granules and stable EC formulations. This allows re-sellers and growers to carry a low-level of product in stock to allow timely fungicidal application. These products do not have any lifespan concerns when correctly stored and are suited to being held over from year to year. Additionally, Imtrade Australia provide stand-alone active ingredient formulations (as opposed to blends) to allow the consultant/grower to tailor their own blends and packages to suit the situation they are presented with. For example, if the situation calls for the addition of azoxystrobin to a triazole brew to assist with triazole resistance prevention, it can be easily managed.
As with all Imtrade Australia’s products, every batch is QC tested to ensure a high quality product is provided and all relevant specifications are met. To assist with your fungal pathogen management, Imtrade Australia supplies the following products;
- Imtrade Turbulence 800WG (800g/kg tebuconazole)
- Imtrade Octopus 800WG (800g/kg epoxiconazole)
- Imtrade Connect 800WG (800g/kg azoxystrobin)
- Imtrade Triadimefon 500WG (500g/kg triadimefon)
- Imtrade Nosclex 800WG (800g/kg procymidone)
- Imtrade Cracker Jack 750EC (550g/L propiconazole)
- Imtrade Defend 400EC (400g/L difenconazole)
- Imtrade Whack 720 (720g/L chlorothalonil)
- Imtrade Cyproconazole 800WG (800g/kg cyproconazole) – registration pending
Beard C et al 2016, ‘Foliar fungicide strategies for Managing Wheat Powdery mildew’ accessed here
Cox B et al 2016, ‘Wheat Powdery Mildew – Using New Fungicide Resistance Detection Methodologies to Stay Ahead of the Game’ accessed here
Written by Michael Macpherson, National Technical Manager, Imtrade Australia