Ascochyta Black Spot of Peas

Ascochyta pisi

Names:

Ascochyta Blight of Field Peas.

Description:

Purplish black streaking of the lower stems which may lead to a girdling rot at the base of the plant and death. Spots on the leaves may be dark brown, small, irregular and scattered over the leaf or may be a few large, circular, brown spots. Dark brown spots on the pods may join to form large sunken purplish black areas. Infected seeds may appear purplish brown or discoloured. Lightly infected seed may look normal.

Species Affected:

Peas.

Biology:

Favoured by moist conditions
Survives on crop residues.
Spread by infected seed, wind and water splash.
The blight is usually caused by a combination of species including Ascochyta pisi, Mycosphaerella pinodes and Phoma medicaginis var. pinodella.

Life Cycle:

Spread on seed, in the soil or on stubble. Infection is mainly by wind borne spores from pea stubble within a few kilometres.
Infection can occur at any stage of growth of the peas.
Epidemics are common in wet weather when spores are also transported by raindrop splash and wind and have a better chance of infecting the wet leaves.
Disease may come from infected seed and in wet years may cause heavy disease loads, but in dry years may have little effect.
It can survive in soil for many years.
Soil borne inoculum can cause severe root rot and lower stem lesions.

Origin and History:

Distribution:

Significance:

Often the most serious disease of peas in the southern regions of Australia.
Yield loss is greatest in wet seasons.

Management and Control:

Destroy pea trash and volunteers.
Plant Peas more than 500 m from previous crops.
Plant more resistant varieties.
Rotate crops so there is at least 3 years between Pea crops and often 4 or 5 years may be required.
Delay sowing to a cooler period of the year e.g. Late June rather than May to early June. Avoid early sowing with high seed rates as this expose more plants to the disease and produces thick crops with high humidity and lodging which favour the disease build up.
Use healthy seed from a crop that was not infected. Test seed for the disease (see Seed testing laboratories).
Treat all seed with P-Pickle T, but note that this may fail if more than 12% of seeds are infected. Apply inoculum before fungicide seed dressing and plant immediately. Don't mix fungicide with inoculants as this will reduce the number of rhizobia.
Apply all foliar fungicide sprays before rain.
Apply first fungicide spray 3-4 weeks after emergence.
Use higher fungicide rates if the disease is observable.
Use fine nozzles at high pressures (4 bar) delivering at least 80 L/ha spray mix.
Control Strategies
Treat seed with 200 mL P-Pickel T per 100 kg seed.
Apply 1 kg/ha mancozeb750 3-4 weeks after planting when rain is expected.
Apply 1 kg/ha mancozeb750 3-4 weeks later when rain is expected. If disease is evident use 1 L/ha chlorothalonil720.
Monitor crop 7-10 days after each rain and if disease is detected apply 1.5 L/ha chlorothalonil720 every three weeks just before rain until pods developed.
When monitoring look for wilting of the upper foliage or small areas of dying plants then search for lesions.

Related and Similar Species:

References:

1294

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.