Crown rot, septoria and other yield-reducing diseases are part and parcel of wheat farming in Australia. Unfortunately, completely avoiding these diseases is almost impossible, and most farms will experience the damaging effects of these nasties at some stage. Treating the diseases and mitigating their effects on crops is key to maintaining productivity and ultimately, profit.
Wheat farming is one of Australia’s major agriculture industries, which is forecast to produce around 26.1 million tonnes in the 2016/2017 growing season. The majority of wheat grown in Australia is sold to overseas markets, and the crop represents one of Australia’s most valuable exports. Our mild winter climates throughout much of the country provide the perfect growing conditions for this winter grain. Despite an excellent outlook for the coming season, wheat production is not without its risks. Crown rot, septoria and other fungal or leaf spot diseases are common difficulties facing wheat farmers around Australia, and can result in significant yield loss if not treated effectively.
Fortunately, wheat farmers have a number of strategies available to them when it comes to dealing with these bothersome infections.
As one of the major factors affecting wheat yield in the northern grain region (northern New South Wales and southern Queensland) as well as southern parts of Australia, crown rot can be tricky to manage. Perfect breeding grounds for this little nasty, which produces the highest prevalence of whiteheads, are a wet beginning to the season, followed by a dry spell before harvest. Although in general, crown rot prefers moderately moist soils, it can occur in many growing conditions, without proper prevention and eradication.
While crop rotation is a go-to approach for many farmers, and may reduce the incidence of this soil-borne disease in future crops, it is often not a sufficient strategy. Unfortunately, the infected stubble can remain in soil and affect future crops indefinitely. Furthermore, fungicides are ineffective in treating crown rot as they are unable to penetrate the plant’s insides, where the fungus is shielded.
So, what are the best ways to mitigate yield loss from crown rot? The best approach is to apply a range of solutions:
Choose your paddock wisely
Avoid paddocks with high incidence of crown rot from the previous season. Test the soil if necessary (the PreDicta B test is designed specifically for this), and choose soil types with better moisture storage.
Try crop varieties with higher resistance to, or tolerance for the disease. Risk of yield loss versus potential crop value are also factors worth considering. According to soilquality.org.au some of the most resistant varieties include Lang, Baxter and Sunco. You can find out more about variety selection from their crown rot fact sheet.
Plant a break crop
Rotating your field with a break crop such as sorghum or canola will give the stubble a chance to break down and thus reduce inoculum levels in the soil. You can then go on to plant wheat in the field for the following season.
Maintain moisture levels in soil
Avoid moisture stress on your plants, as this will increase their susceptibility to the disease. Avoid burning off in hot seasons, as this will only remove diseased components of the plant from above the soil (not affecting the infected roots and materials that remain below the soil) and will also increase the likelihood of moisture reduction and erosion in the soil. If you must burn, do so as close to sowing season as possible.
Ensure adequate nutrition in the soil
Specifically, ensure that levels of zinc are ample—but be careful to limit early nitrogen application.
Septoria Tritici Blotch
Much the same as crown rot, septoria tritici blotch (STB) survives within the stubble of the wheat crop. It is a particularly troublesome disease affecting crops across Australia, due to its propensity to develop fungicide resistance. As STB thrives in environments of heavy rainfall, it can be particularly prolific in the southern grain growing regions of Victoria and South Australia. The disease can spread over wide areas, due to its occurrence in wind-borne spores, as well as throughout its immediate vicinity via raindrop splashing from infected leaves. The brown and silver-grey blotches which occur on the leaves of effected plants are the key indicator for STB, as well as black fruiting spots which occur upon the dead sections of leaf.
Treatment and risk mitigation options for septoria are very similar to those of crown rot, however also include the use of fungicides:
Crop rotation and break crop planting
STB can remain alive in soil for up to 18 months, which is why The Grains Research and Development Corporation (GRDC) recommends rotating wheat crop out for at least one year. This will reduce the likelihood of surviving STB fungus in the soil between wheat crops. Planting a break crop will also aid in this mitigation, as will planting less susceptible varieties. (See the wheat variety sowing guide from Primary Industries and Regions SA)
Burning or burying stubble from the harvested crop will reduce the inoculum and risk of future infection, however cannot control the blow-in of diseased spores from nearby fields. Burning will also increase the risk of soil erosion and moisture stress—keep this in mind before doing any burning!
Due to the risks of fungicide-resistance developing in STB strains, the use of fungicides is advised against, where possible. If performed effectively, crop rotation and stubble management can help to reduce the risk of septoria infection in crops. However, if heavy rainfall has occurred in the early seeding stages of wheat crop growth (where most STB occurs), it may be necessary to use disease control. A resistance avoidance strategy is very important, in these cases. You can find out more about effective strategies against developing assistance in the GRDC’s septoria tritici blotch fact sheet.
Other pesky diseases
There are, worryingly, a wide array of diseases that wheat crops are particularly susceptible to. Fortunately, many of their treatment and management options are similar in nature, and can be performed effectively to mitigate yield loss and eradicate disease. Some of the other diseases to look out for, along with their treatment alternatives include:
Common root rot
Often found in crops affected by crown rot, common root rot can result in stunted plants and reduced yield. Crop rotation, planting of break crops and avoiding burning are advised here, once again.
Root lesion nematode (RLN)
RLN is characterised by dark brown lesions on the root of the plant, however can only be verified by laboratory testing. The disease can spread through transfer from farm machinery and also via surface water. It is important to introduce practices into farming which limit the spread – such as regular cleaning of farm equipment and good management of ground water (effective drainage).
This menacing wheat disease affects the whole of the infected plant, and is easily detectable, with distinctive black, rotted roots and whiteheads. Fungicide can be used as a seed treatment, along with grass-selective herbicides before cropping. Furthermore, the crop rotation and break crop methods described above can assist with preventing future outbreaks in affected fields.
For more information on other diseases which can affect your wheat crop, you can visit the NSW Department of Primary Industries website, and download their fact sheet titled ‘Root and Crown Diseases of Wheat and Barley‘.