PestFacts WA

Sclerotinia apothecia are being found

• Walkaway

• Gibson (DPIRD’s Esperance Downs Research Station)

DPIRD officers Ciara Beard and Anne Smith have reported finding sclerotinia apothecia in a canola crop at Walkaway. The canola was at the cabbage stage (nine leaf) and the apothecia was found in a part of the paddock that was sown with lupins last year. The apothecia were light brown in colour, not the usual bright white they often come up as in the Geraldton area, indicating they have possibly been present for a week or more. Recent regular rain and cooler temperatures in the area will have suited their germination which signals the start of the sclerotinia cycle.

Sclerotia in a depot at the Esperance Downs Research Station (near Gibson) have also just started to germinate and produce apothecia.

These findings are a warning that the sclerotinia disease cycle is commencing in the northern and south coastal wheatbelt.

Apothecia are small cream-apricot coloured mushroom cups measuring 5-15mm in diameter that appear from the germination of sclerotia (hard black fruiting bodies/resting structures of sclerotinia) under favourable conditions. While they can vary somewhat in colour, they all tend to darken over time and can survive for around three weeks before withering away.

Carefully digging out the apothecia will usually show you its connection back to the sclerote it germinated from.

Apothecia release massive numbers 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). These infected petals fall into the crop canopy and under humid damp conditions can cause stem infection - this is the most common infection pathway. In some years, particularly under very wet conditions in paddocks that have high inoculum levels, basal infections pre-flowering have been observed. Basal stem infections can develop from infected leaves that touch the ground or direct growth over/under the soil from sclerotia to the stem. White masses that are fungal hyphae (on leaves, soil or stem bases) are the key symptom to look for.

Growers are urged to start planning for sclerotinia management in their canola crops.

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. These may require fungicide protection.

Growers need to consider the following factors to determine their risk of sclerotinia:

• 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.

A new tool is available for use during crop flowering to help growers/consultants determine the likely economic returns from applying fungicide at a specific time during flowering. DPIRD’s free SclerotiniaCM app can aid in fungicide decision making once the crop is in the early bloom stage. The app uses a forecasting model and the user can specify individual paddock data/history as well as recent and expected weather conditions so that the output relates to their own cropping circumstances. The SclerotiniaCM app can be downloaded from the App Store or Google Play Store onto your iPad or Android tablet.  For more information refer to DPIRD’s SclerotiniaCM app page.

Several fungicide products that are made up of the active ingredients prothioconazole + tebuconazole, procymidone, iprodione, prothioconazole + bixafen and more recently azoxystrobin + tebuconazole 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. Use the SclerotiniaCM app for guidance.
• A second fungicide application at 50% (full) bloom is only beneficial in seasons with an extended wet period. Use the SclerotiniaCM app for guidance.
• 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.

Growers and consultants are encouraged to report to the PestFax service any apothecia finds or disease observations as the season progresses.

Further information can be found at the department’s Managing sclerotinia stem rot in canola page and GRDC’s Sclerotinia stem rot in canola fact sheet.

For more information on sclerotinia contact plant pathologists Ciara Beard, Geraldton on +61 (0)8 9956 8504 or Andrea Hills, Esperance on +61 (0)8 9083 1144.

Article authors: Ciara Beard (DPIRD Geraldton), Jean Galloway (DPIRD Northam) and Andrea Hill (DPIRD Esperance).