Identification & Management of Field Crop Diseases in Victoria

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Bacterial Blight of Field Pea

This disease, caused by the bacteria Pseudomonas syringae pv. pisi and P. syringae pv. syringae, is a serious disease of field pea. Recent surveys for bacterial blight in Victoria and southern New South Wales have shown the pathogen P. syringae pv. syringae as the main cause of the disease in commercial crops. Bacterial blight is widespread in field peas in southern New South Wales and Victoria, but its severity varies greatly from crop to crop and between seasons. The disease is seed borne and is more prevalent after frost events or radiating from wheel tracks; multiple frosts can cause epidemics resulting in significant yield loss.

What to Look For

  • Bacterial blight first appears as small, dark green, water-soaked spots on leaves and stipules, often near the leaf base. The spots enlarge and merge but are often limited by the veins.
  • The leaf spots turn yellowish and later brown and papery.
  • Spots on pods are sunken and olive brown.
  • Spots can develop on the stem near ground level. These begin as water-soaked areas that later turn olive-green to dark brown. Stem lesions may coalesce, causing the stem to shrivel and die.
  • Stem lesions may spread upwards to the stipules and leaflets. In this case, a fan-like lesion is formed on the stipule. Spots can merge causing the stem to shrivel and die.
  • Pre-emergence and post emergence damping-off may occur and even advanced plants may be killed. Heavily infected seed may be discoloured, but light infection has no visible effect on seed.

The symptoms of bacterial blight caused by Pseudomonas syringae pv. pisi or Pseudomonas syringae pv. syringae are indistinguishable from each other.

Whole field pea plant affected by bacterial blight

Leaf lesions caused by bacterial blight.

Water soaked lesion spreading into the leaf from the base caused by bacterial blight

Water soaked lesion spreading into the leaf from the base caused by bacterial blight.

Disease Cycle

Bacterial blight commonly becomes established within a field by sowing infected seed or from infected pea trash that is nearby. During wet weather, bacteria spread from infected to healthy plants by rain splash and in wind-borne water droplets.

Infection may occur at any stage of plant growth. The pathogens can remain on the surface of plants without causing symptoms. However, following rain, heavy dew, frost or other forms of damage to plant tissues, symptoms can develop. Damage to field pea provides entry of bacteria into the plant tissue. Early infections may lead to epidemics, but later infection can also cause yield losses. Disease outbreaks tend to be worse in years with frequent frost events and frequent rainfall that enable the disease to become established and spread. A combination of excessive rainfall and strong winds provides the most favourable conditions for spread of the disease within crops.

Pseudomonas syringae pv. pisi is largely restricted to field peas while P. syringae pv. syringae has a wide host range including clover, common beans, faba beans, lentils, chickpeas and vetch which act as alternate hosts.

Disease cycle of bacterial blight in field peas

Disease cycle of bacterial blight in field peas. Illustration by Kylie Fowler.


Bacterial blight can be avoided by using an integrated approach to management that encompasses planting disease-free seed, crop rotation, variety selection and avoiding early sowing.

Use of Disease Free Seed

This is the main control measure recommended. The use of clean seed will minimise the possibility of disease, provided the land has not been cropped to peas for several years. Do not use seed from crops identified with bacterial blight during field inspections. A field inspection should occur at mid to late pod fill and/or after every frost event. Bacteria remain viable on seed for at least 2 years.

Cereal stubble

Field pea crops sown into a mulch of cereal stubble are more likely to develop bacterial blight. In winter, the covering of cereal stubble acts to insulate the soil surface and keep temperatures cool, which predisposes field pea plants to frost injury. If sowing field pea into cereal stubble, keep the stubble standing.


To obtain a bacterial blight-free crop, pea should not be sown on land sown to pea in the previous year or adjacent to pea stubble. Where possible, pea should not be grown on the same land more than once in three years. If disease occurs the rotation should be extended to once in four years.

Stubble can be a significant source of inoculum. Destroy by burying, baling or burning infected stubble. The survival time of inoculum is significantly reduced by burying pea trash 10 cm below the soil surface.

Time of Sowing

Early sown crops are more vulnerable to bacterial blight infection than late sown crops; never sow earlier than recommended for your district. In areas prone to bacterial blight avoid early sowing.

Crop Damage

Bacterial blight is often associated with physical crop damage such as hail, frost, strong winds, sand blasting or machinery damage. Physical damage enables bacteria to enter plant tissue. Minimise the use of post emergence herbicide sprays, if possible, as the severity of bacterial blight can increase if plant tissue is damaged. Avoid paddocks where sulfonylurea residues may be present and the more frost-prone paddocks.


The frequency of bacterial blight can be reduced by avoiding varieties susceptible to Pseudomonas syringae pv. syringae and sowing those that have better resistance.

Farm Hygiene

When bacterial blight is detected, steps should be taken to prevent the spread of disease. This includes restricting access to the affected area. Where possible, harvest infected crops last to avoid contaminating healthy crops and machinery used in an infected crop should be cleaned thoroughly and washed with disinfectant after use. Likewise, machine operators and farm workers should only move from crop to crop after taking precautions against the spread of bacteria. This is best achieved by wearing rubber boots and waterproof trousers that are washed with disinfectant immediately after leaving an infected field. Crops should never be inspected when they are wet as this increases the chance of spreading disease.

Chemical Control

Fungicides and seed treatments are designed to be active against fungal diseases and are ineffective in the control of bacterial diseases. There are copper based compounds, registered for use in field peas against bacterial blight, but evidence for their effectiveness in Australian field pea crops is limited and inconclusive.

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