Powdery Mildew of Field Peas

Note Number: AG0147
Published: May 2004
Updated: August 2012 

Powdery mildew can be a serious disease of field peas grown in Victoria. It occurs sporadically when warm humid conditions favour its growth late in the season. It can be controlled through crop rotation, variety selection and strategic use of foliar fungicides.

What to look for

Fig 1. Powdery mildew on field pea leaf and stipule

Infected plants are covered with a white powdery film, and severely infected foliage is blue-white in colour; tissue below these infected areas may turn purple. All aerial parts of the plant may become infected resulting in withering of the whole plant.

Severe pod infection can cause a grey-brown discolouration of the seeds. These seeds have an objectionable flavour that lowers the quality of the grain (See figures 1 to 3).

Disease Cycle

Fig 2. Powdery mildew on field pea pod

The disease powdery mildew, caused by the pathogen Erysiphe pisi, oversummers on infected pea trash and produces spores which are blown by wind into new crops. The disease may also be seed-borne, but this source of infection is usually less important.

Under favourable conditions, the disease may completely colonise a plant in 5-6 days. Once a few plants become infected, the disease rapidly spreads to adjacent areas. Warm (15-25°C), humid (over 70% RH) conditions for 4-5 days late in the growing season, during flowering and pod filling, favour disease development. However, heavy rainfall is not favourable for the disease as it will actually wash spores off plants. Night time dews are sufficient for the disease to develop.

Economic Importance

Fig 3. Powdery mildew resistant plant beside a badly infected plant.

Severe infections can reduce yield by 10–20%. Powdery mildew is most prevalent late in the season.

Crops sown late are more likely to be affected by powdery mildew than early sown crops. Severe pod infection can lead to poor seed quality.

Management

Varietal selection

Growing a resistant variety is the most effective means of controlling powdery mildew. Maki and Yarrum are the resistant varieties currently available (See Table 1).

Crop rotation

• Leave a four year break between growing field pea crops in the same paddock.
• Control volunteer field peas, which can harbour disease.
• Avoid sowing field pea crops adjacent to last season’s stubble.
• Incorporate or burn infected pea stubble soon after harvest where practicable.

Foliar fungicides

• Monitor crops from flowering onwards.
• Check across the whole paddock, as disease severity may be variable.
• Early detection and early spraying are critical.
• The fungicides are protectants, and will only protect the uninfected foliage they are sprayed onto.
• Fungicides for powdery mildew have limited systemic activity, and will not protect the growth occurring after application.
• Good plant coverage with the fungicides is essential.
• Depending on disease pressure, foliage is protected for about 14 days.
• Before using any chemicals check that they are currently registered for use.

Further references

Pulse Australia
Pulse Disorders: The Ute Guide
Pulse Seed Treatments and Foliar Fungicides

Contact/Services available from DPI

DPI Field Crops Pathology, Grains Innovation Park, 110 Natimuk Rd, Horsham 3400. Tel (03) 5362 2111, or the DPI Customer Service Centre 136 186

Acknowledgement

This Information Note was originally written by Trevor Bretag, May 2001 and was updated by Helen Richardson, June 2008. The current version was reviewed by Helen Richardson and Frank Henry, BioSciences Research - Farm Services Victoria, May 2010 and August 2012. Financial support by the GRDC is gratefully acknowledged.