Sclerotinia apothecia are being found
DPIRD officers Ciara Beard and Anne Smith have reported finding a sclerotinia apothecia this week at Geraldton. It was found under advanced wheat plants. This is the first report for this season and follows substantial weekly rainfall at the site since the season break in early June.
This finding is a warning that the sclerotinia disease cycle is commencing in the northern wheatbelt.
Plant pathologist Ravjit Khangura (DPIRD) has also reported finding sclerotinia apothecia in her backyard, near bottle gourd affected by sclerotinia, in the Perth metropolitan area.
Apothecia are little cream coloured mushrooms measuring 5-15mm in diameter that appear after carpogenic germination of sclerotes (hard black fruiting bodies/resting structures of sclerotinia) under favourable conditions. Apothecia release massive amounts of ascospores that cause sclerotinia stem rot predominantly via infecting petals in all broadleaf crops including canola, lupins, chickpeas, lentils, field peas, faba beans, lucerne and weeds (wild radish and cape weed).
Growers are urged to start planning for sclerotinia management in their canola crops.
Despite dry start to the season, weather conditions seem to be favourable for sclerotinia spore release in some parts of the grainbelt and therefore elevating the risk for disease outbreaks in flowering canola.
DPIRD research over the past few years has shown that as a rule of thumb regular rainfall and high humidity (>75%) in the three weeks before and after commencement of flowering are most conducive for the damaging levels of disease to occur in crops. Although canola crops are at variable growth stages in the state, the most vulnerable canola crops are the ones that have just started to flower or are flowering as infected petals dropping onto plants initiate infections. These may require fungicide protection.
Growers need to consider the following risk factors:
- rotation history of the paddock
- history of sclerotinia in the current canola and surrounding paddocks
- rainfall events before and after flowering
- growth stage of canola.
In Western Australia, two pathways of sclerotinia infection have been reported. The most common infection pathway is via infected petals, however, basal infections pre-flowering have been frequently observed in some years particularly under very wet conditions in paddocks that have high inoculum levels. Basal stem infections can develop from dying leaves that touch the ground or direct growth to the stem over/under the soil from sclerotia. White masses that are fungal hyphae (on leaves, soil or stem bases) are the key symptom to look for.
Growers and consultants are advised to assess their risk of sclerotinia and be prepared to apply fungicide if the risk is moderate to high. Growers also need to keep an eye out for basal sclerotinia infections in high risk paddocks. Download the free app SclerotiniaCM app to aid in fungicide decision making.
Several fungicide products that are made up of the active ingredients prothioconazole + tebuconazole, procymidone, iprodione and more recently prothioconazole + bixafen are registered for the control of sclerotinia in canola. Fungicides need to be applied as recommended per product label.
Based on the extensive research conducted by DPIRD over the last few years the following in-season sclerotinia management options are recommended;
- Apply a single foliar application at 30-50% bloom, provided conditions are favourable for infection before and during flowering. See Table 1 below for recognising bloom stages in canola.
- A second fungicide application at 50% (full) bloom is only beneficial in seasons with an extended wet period.
- If growers notice ground infections they can apply a foliar fungicide immediately or wait until 20% bloom to prevent further new infections.
- Fungicide application is still warranted in crops with wide row spacing (up to 44cm) if the seasonal conditions (high rainfall and humidity) become favourable during flowering.
|Percent bloom||Number of flowers open on the main stem|
|20% (petal drop commences)||11-14|
Growers and consultants are encouraged to report to the PestFax service any apothecia finds or disease observations as the season progresses.
For more information on sclerotinia contact plant pathologists Ciara Beard, Geraldton on +61 (0)8 9956 8504, Ravjit Khangura, South Perth on +61 (0)8 9368 3374 or Andrea Hills, Esperance on +61 (0)8 9083 1144.