Ascochyta Disease in Field Peas
Ascochyta blight of field pea is a disease complex caused by three closely related fungi; Ascochyta (Mycosphaerella) pinodes, A. pinodella and A. pisi. The disease complex is usually most severe in growing seasons with high rainfall. Yield losses in field peas of up to 80% have been reported due to A. pinodes. Ascochyta - infected seeds usually have low germination and poor emergence.

Appearance: Seedlings form infected seeds may show a blackening of the stem tissue from the soil line upward for 5 to 15 cm. Seedlings usually survive but in a weakened condition. Symptoms on leaves, stems, flowers and pods vary, depending on the fungus involved. On leaves and stipules early infections of A. pinodes are seen as purplish flecks with irregular margins. On older leaves or under favorable weather conditions the spots may enlarge and cause the leaf to dry up. On stems, A. pinodes produces purplish black lesions which eventually may girdle the stem causing extensive blighting. Petal infection causes the blossoms to fall off. Infected pods usually show a purplish-brown discoloration. Seeds within diseased pods may exhibit discoloration or shrinkage.

Ascochyta pinodella lesions are similar in appearance to those of A. pinodes but develop near or just above the soil line, causing so-called foot-rot.

Spots caused by A. pisi on leaves, stems and pods are tan or brown in the centre with a darkened margin. Large stem and pod lesions tend to be sunken. The centres of lesions may be speckled with black fruiting bodies.

Disease Cycle: All three fungi can be seed-borne. Infected seed is the most important means of transmission for Ascochyta pisi, which is a weak saprophyte and does not survive long in soil. Ascochyta pinodes and A. pinodella are vigorous saprophytes colonizing pea residues both on and below the soil surface. Spores of A. pinodes and A. pinodella are spread by wind and rain splash. Spread of A. pisi is almost entirely by rain splash.

Disease Control:
a) Use disease-free or lightly infected seed. Seed infected by Ascochyta species usually has lower germination and poorer plant emergence than healthy seed. This is especially the cause under environmental conditions such as low temperature and high moisture content. If heavily infected seed must be planted, chemical seed treatment may be beneficial.
b) Crop rotation - Grow peas no more than once in four years in a given field and avoid planting next to the previous year's pea fields.
c) Resistance - Some field pea cultivars are slightly more tolerant to the disease complex than others. More research is required in this area.
d) The fungicide Bravo is registered as a Foliar spray against Ascochyta pinodes. More than one application may be necessary, beginning at early bloom.

Back to Testing for Disease

Home | News | About | Seed Testing | Private Customers | Contact

Discovery Seed Labs Ltd.
450 Melville Street
Saskatoon, Saskatchewan
S7J 4M2

Phone:(306)249-4484
Fax:(306)249-4434