Key message
- Diseases vary by season, but correct identification helps guide successful management and feeds into national disease-monitoring programs.
The most important aspect of managing plant diseases is correct identification of the issue.
A proper diagnosis ensures the right advice can be provided by pathologists and agronomists and avoids unnecessary application of in-crop fungicides by growers.
With GRDC co-investment, through the Grains Agronomy and Pathology Partnership (GAPP), the NSW Department of Primary Industries (DPI) provides a diagnostic service to NSW cereal growers and their advisers.
Collating inquiries and the management advice given provides an annual snapshot of the key biotic and abiotic constraints to cereal production (Table 1), which is further supported by annual random cereal crop surveys.
Table 1: Cereal diagnostics and inquiries processed across NSW in 2019 and 2020. Diseases or issues are ranked in order or frequency in 2020. Note that some samples had more than one disease or issue but only the dominant one is recorded in numbers below. *Non-disease issues
Disease/issue | 2020 | 2019 |
|---|---|---|
Stripe rust (wheat) | 194 | 13 |
Scald | 65 | 4 |
*Physiological/melanism | 65 | 10 |
Powdery mildew | 65 | 1 |
Spot form of net blotch | 63 | 32 |
Fusarium crown rot | 49 | 14 |
*Frost damage | 44 | 4 |
*Other non-disease (such as soil constraint, leaf blotching) | 33 | 24 |
Leaf rust (wheat) | 33 | 2 |
Bacterial blight (other cereals) | 30 | 0 |
Rusts crown and stem (oats) | 28 | 4 |
*Herbicide | 28 | 6 |
Net form net blotch | 23 | 0 |
Bacterial blight (oats) | 22 | 3 |
Barley grass stripe rust | 20 | 1 |
Barley yellow dwarf virus | 19 | 1 |
Septoria tritici blotch | 17 | 13 |
*Nutrition | 16 | 2 |
Take-all | 13 | 1 |
Rhizoctonia | 12 | 7 |
Yellow leaf spot | 10 | 4 |
Loose smut | 9 | 1 |
Fusarium head blight | 9 | 0 |
Seedling root disease complex (Pythium, crown rot, Rhizoctonia, take-all) | 8 | 2 |
Septoria (oats) | 3 | 2 |
Wheat streak mosaic virus | 3 | 1 |
Common root rot | 2 | 3 |
Ryegrass rust | 2 | 0 |
Ergot | 1 | 0 |
Red leather leaf | 1 | 7 |
Sclerotium rolfsii | 1 | 2 |
Spot blotch | 1 | 0 |
Ring spot | 0 | 1 |
Total | 889 | 165 |
Source: Dr Steven Simpfendorfer and Dr Andrew Milgate
Correct diagnosis
Evidence-based methods are used to confirm diagnosis, comprising a combination of visual symptoms, crop management history and distribution in the paddock, as well as the recovery and identification of the causal pathogens using microscopy and other laboratory techniques.
Suspect virus samples are confirmed through laboratory testing using ELISA (an immunological assay used to measure biological samples) at NSW DPI’s Elizabeth Macarthur Agricultural Institute at Menangle.
Wheat, barley and oat rust samples (stripe, leaf and stem) are sent to the Australian Cereal Rust Control Program at the University of Sydney to help track pathotype populations and distribution across Australia.
Seasonal variation
Not surprisingly, individual seasons have a strong influence on the level of inquiries received from growers and advisers. There were five times more inquiries in the wetter 2020 season (889), which was more conducive for the development of a range of cereal leaf and head diseases, compared to the drier conditions in 2019 (165).
The four main cereal diseases in 2020 were wheat stripe rust (with widespread distribution of the newer Yr198 pathotype), scald in barley, powdery mildew in wheat and barley, and spot form of net blotch in barley (Table 1).
In 2019, the four main cereal diseases were spot form of net blotch in barley, Fusarium crown rot, wheat stripe rust and Septoria tritici blotch.
Interestingly, the levels of yellow leaf spot (Pyrenophora tritici-repentis) diagnosed in both seasons were relatively low. However, wheat samples with leaf blotches or mottling suspected to be caused by yellow leaf spot were submitted each year. Growers and advisers continue to find it difficult to accurately diagnose this particular leaf disease, which is often confused with Septoria tritici blotch (Zymoseptoria tritici), Septoria nodorum blotch (Stagonospora nodorum) and physiological responses to abiotic stress such as nitrogen movement in plants.
The 2020 season also highlighted the fact that diseases such as take-all, which have not been seen at damaging levels for many years, can quickly re-emerge under conducive conditions.
Individual seasons have a strong influence on the level of inquiries received from growers and adviser.
The number of rust and powdery mildew samples received from susceptible wheat varieties in 2020 highlights how important genetic resistance is in integrated disease management systems. Susceptible varieties are more reliant on fungicide applications to limit disease levels and yield loss, which can increase the risk of fungicide resistance developing.
Importantly, no disease was found in at least one in five samples submitted for disease diagnosis – 21 per cent in 2020 and 28 per cent in 2019 (highlighted with an asterisk in Table 1). These samples were either diagnosed as being plant physiological responses to stress, frost damage or herbicide injury, or related to crop nutritional issues.
This highlights the ongoing importance of the diagnostic service provided by these projects to NSW growers and advisers to support correct identification and implementation of appropriate management strategies.
More information: Dr Steven Simpfendorfer, 0439 581 672, steven.simpfendorfer@dpi.nsw.gov.au; Dr Andrew Milgate, 02 6938 1990, andrew.milgate@dpi.nsw.gov.au