Powdery mildew, caused by the pathogen Erysiphe pisi, can be a serious disease of peas in South Australia and Victoria. Severe infections can significantly reduce yield in susceptible varieties. Powdery mildew is most prevalent late in the season when warm days and cool nights result in dew formation.
Note: Downy mildew is caused by Peronospora viciae and is not the same fungus that causes powdery mildew.
Infected plants are covered with a white powdery film. Severely infected foliage turns blue-white in colour; tissue below these infected areas may turn purple, (Figures 7.12 and 7.13). Symptoms first appear on the upper surfaces of the oldest leaves. Leaves, stems and pods may all 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.
Figure 7.12 Typical white powdery growth on an infected plant
Figure 7.13 Powdery mildew infects all of the plant including pods
The fungus over-winters on infected pea trash and produces spores which are blown by wind into new crops, (Figure 7.14). Under favourable conditions the disease may completely colonise a plant in 5 - 6 days and once a few plants become infected it rapidly spreads to adjacent areas.
Warm (15 – 25°C), humid (over 70 percent) conditions for 4 – 5 days late in the growing season during flowering and pod filling are favourable for disease development. Rainfall is not favourable for the disease, as it will actually wash spores off plants. Dewy nights are sufficient for disease development.
The disease may also be seed-borne, but this source of infection appears less important.
Figure 7.14 Disease cycle of powdery mildew of field peas. Illustration by Kylie Fowler
Growing a resistant variety is the most effective means of controlling powdery mildew. Maki and yarrum are the resistant varieties currently available. For further information on disease ratings refer to the Victorian Pulse Disease Guide.
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.
Seed treatments can be beneficial and are recommended for districts where powdery mildew frequently occurs. For more information on seed treatments, see the Pulse Australia Bulletin Pulse Seed Treatments and Foliar Fungicides.
Monitor crops from flowering onwards for signs of powdery mildew. If the disease is present the application of a foliar spray may be warranted. Fungicides need to be applied prior to disease development to be most effective. Fungicides for powdery mildew have limited systemic activity and will not protect the new growth following spraying. 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. Refer to the Pulse Australia Bulletin Pulse Seed Treatments and Foliar Fungicides for more information on foliar fungicides.
Note: Fungicides used to control downy mildew have no activity against powdery mildew.
DOWNY MILDEW OF FIELD PEAS
SEPTORIA BLIGHT OF FIELD PEAS