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Low levels of disease persist during the drier summer season in parts of the northern region

Summer crop paddocks across northern New South Wales, southern Queensland and central Queensland, were surveyed to monitor fungal and bacterial diseases present in the 2018-2019 summer cropping season. In comparison to the 2017-2018 season, it was drier (Figure 1), making it unfavourable for most grain crop diseases to develop. Observations for maize, mungbeansorghum, soybean and sunflower are given below. 

Figure 1. Temperature and precipitation during the growing period of summer grain crops in the northern region for 2017-2018 (Source: Australian Bureau of Meteorology)

Figure 1. Temperature and precipitation during the growing period of summer grain crops in the northern region for 2017-2018 (Source: Australian Bureau of Meteorology)

Figure 2. Temperature and precipitation during the growing period of summer grain crops in the northern region for 2018-2019 (Source: Australian Bureau of Meteorology)

Figure. 2. Temperature and precipitation during the growing period of summer grain crops in the northern region for 2018-2019 (Source: Australian Bureau of Meteorology)

Most maize paddocks surveyed were free from disease except for:

  • One paddock in Jondaryan with low incidence of common boil smut (Ustilago maydis)
  • One paddock in northern NSW heavily infected with grey leaf spot (Cercospora zea-maydis)

Figure 3. Boil smut of maize (Photo D.L. Adorada)

Figure 3. Boil smut of maize (Photo D.L. Adorada)

Figure 4. Grey leaf spot on maize (Photo D.L. Adorada)

Figure 4. Grey leaf spot on maize (Photo D.L. Adorada)

Due to dry conditions and rains too late in most locations, fewer mungbean crops were planted than usual. 

The diseases that were most commonly observed were:

  • Tan spot, caused by Curtobacterium flaccumfaciens pv. flaccumfaciens was found in low to moderate incidences (1-30%) in southern Queensland, due to favourable dry and hot weather
  • Gummy pod was present in a few paddocks in southern Queensland (25% incidence) and northern NSW (15% incidence)
  • Fusarium wilt at low incidence (<5%)

Figure 5. Tan spot on mungbeans, Formartin southern Queensland (Photo D.L. Adorada)

Figure 5. Tan spot on mungbeans, Formartin southern Queensland (Photo D.L. Adorada)

Figure 6. Gummy pod in mungbeans, Formartin southern Queensland (Photo D.L. Adorada)

Figure 6. Gummy pod in mungbeans, Formartin southern Queensland (Photo D.L. Adorada)

Precipitation played an important role in disease incidence in sorghum. Northern NSW and central Queensland had enough soil moisture at post-flowering which saved the sorghum crop from diseases induced by moisture stress, charcoal rot (Macrophomina phaesolina) and Fusarium stalk rot (Fusarium spp.). 

In contrast, in southern Queensland, where there was low or no precipitation during the post-flowering months of mid-January to mid-March, high levels of stalk rots, particularly charcoal rot was observed. 

Charcoal rot was prevalent in Dalby, Chinchilla, Bowenville and MacAlister, whereas incidence of Fusarium stalk rot was high in Dalby and MacAlister, albeit at low levels in most of the paddocks surveyed.

A paddock in Clermont central Queensland was heavily infected by black mould, caused by several species of dark pigmented fungi such as Alternaria, Aspergillus, Curvularia and Penicillium. Infected seeds will have reduced quality, size, viability and storage life. Prolonged periods of warm, wet weather favours development of this disease (English et al, 2005).

Figure 7a. Sorghum lodging and charcoal rot, Dalby southern Queensland (Photo D.L. Adorada)

Figure 7a. Sorghum lodging and charcoal rot, Dalby southern Queensland (Photo D.L. Adorada)

Figure 7b. Sorghum lodging and charcoal rot, Dalby southern Queensland (Photo D.L. Adorada)

Figure 7b. Sorghum lodging and charcoal rot, Dalby southern Queensland (Photo D.L. Adorada)

Figure 8. Fusarium stalk rot of Sorghum, MacAlister south eastern Queensland (Photo D.L. Adorada)

Figure 8. Fusarium stalk rot of Sorghum, MacAlister south eastern Queensland (Photo D.L. Adorada)

Figure 9. Black mould in Sorghum, Clermont central Queensland (Photo D.L. Adorada)

Figure 9. Black mould in Sorghum, Clermont central Queensland (Photo D.L. Adorada)

Soybean crops were planted only in a few irrigated paddocks. 

No disease issues were present on the crop paddocks surveyed in Bongeen, southern Queensland.

Figure 10. Healthy soybean in irrigated paddocks, Bongeen (Photo D.L. Adorada)

Figure 10. Healthy soybean in irrigated paddocks, Bongeen (Photo D.L. Adorada)

Very few sunflower crops were planted due to limited rains, thus too late for commercial plantings in most locations. 

No disease issues were found or reported from the sunflower paddocks that were surveyed in central Queensland (2 paddocks), southern Queensland (5 paddocks) and northern NSW (1 paddock).

Figure 11. Sunflower crop, Allora (Photo D.L. Adorada)

Figure 11. Sunflower crop, Allora (Photo D.L. Adorada)

Figure 12. Sunflower crop, Kingsthorpe (Photo D.L. Adorada)

Figure 12. Sunflower crop, Kingsthorpe (Photo D.L. Adorada)

What can be done

In preparation for the next summer cropping season, the best disease management option is to practice preventive measures, to minimise incidence of the disease. Disease management options are described in the following resources:

GrowNotes

Re-visiting management options for charcoal rot in sorghum

Click here for disease diagnostic support

Acknowledgement

Precila Gonzales, USQ Centre for Health

Vicki Green, GRDC

Agronomists and growers from NNSW, SQ and CQ

References

English M, Cahill M, Grains Research and Development Corporation (Australia), Queensland. Department of Primary Industries and Fisheries, 2005, Sorghum disorders: the ute guide, Queensland : Dept. of Primary Industries and Fisheries

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