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Field Pea – Diseases

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Healthy Pea Field

Disease Prevention

Pea crops are subject to a number of diseases that can reduce yield and quality, and infection can come from a variety of sources. These diseases can be minimized through preventative management. Disease prevention recommendations include:

  1. Use of effective crop rotations. Plant peas only once every four years in the same field. Avoid planting adjacent to last year’s pea field or other susceptible broadleaf crops as many diseases are wind-borne and very mobile, and continuous production can increase some seedling diseases and Sclerotinia.
  2. Use the best seed available. A seed test will indicate the presence of seed-borne diseases.
  3. Use of a registered fungicide seed treatment may be warranted, especially if seeding early into cool, wet soils.
  4. Use varieties with disease resistance, such as powdery mildew resistance.
  5. Early seeding.
  6. Monitoring of fields for diseases. 

Scouting your field for diseases

Scouting is one of the most powerful practices to effectively manage crops. It allows early detection of disease symptoms, provides opportunity for mitigation of spread and minimizes the impact on yield.

  • Develop a systematic approach beginning soon after crop emergence.
  • ALWAYS bring along a shovel to dig up plants, pulling plants will not work when assessing root and nodule health.
  • Scout weekly beginning after the crop emerges until maturity, first looking at plant stand, then root/seedling diseases, and as the crop develops for foliar diseases.
  • Take photos, mark problem areas in the field, collect whole plants (leaves, stems and roots) for identification of the disease (put in plastic Ziploc, label with date and location and keep cool until sent to lab).
  • Check in a ‘W’ shaped pattern in the field stopping at 5-10 locations,
  • Take note of yellowing patches, and problem areas in the field, these are often the source of disease spread and if recurring problems are noted these areas may benefit from a separate management strategy.

Scouting, Government of Alberta

Plant Disease Scouting 101, Government of Saskatchewan Fact Sheet.  

Fungicide Application

Keeping crops healthy and disease free is a priority for producers and one practice that can help achieve these goals is applying fungicide. Producers need to consider both disease risk and economics when deciding whether to apply a fungicide.

Disease risk is influenced by the field history (crop rotation, levels of disease in previous susceptible crops; the environmental conditions such as temperature and precipitation levels that may favour disease development; and the level of variety resistance to the disease). A fungicide should only be applied if the risk of disease is high and an economic return is expected. 

Once a decision has been made to apply fungicide, the two most important considerations are timing and coverage. Plant growth and disease progress can be very rapid so it’s essential to be ready to apply the fungicide when it’s needed. Missing the ideal window is very costly and a fungicide applied at the wrong time can lose much of its effectiveness

Good coverage is also critical for a fungicide to be effective. To achieve this, target the plant part that needs protection, be it the leaves, stems, or leafstalks, and do so with adequate droplet density. This is because most fungicides do not move from one part of the plant to another very well. That is why it is important to understand the disease, including which plant parts must be covered by spray and where – top, middle, or bottom – they are in the canopy. Then assess how easy it will be for a spray to reach the target zone.

Determine if more than one application should be done by scouting.  If applying more than one application, make sure to rotate fungicide groups and do not use a single mode of action more than once. Consult the product’s label.  (Forsythe, Trudy K. “Timing and Coverage are Important Factors in Fungicide Application”)

Management of Fungicide Resistance

Just as with different herbicide groups, fungicide groups also have the potential to develop resistance in the disease population. Any fungal pathogen population may contain some strains naturally insensitive to various fungicides. A gradual or total loss of disease control may occur if these fungicides are used repeatedly in the same fields. Other resistance mechanisms that are not linked to site of action, but are specific for individual chemicals, such as enhanced metabolism, may also exist.

To delay fungicide resistance/insensitivity

  • Use a fungicide rotation – rotate the use of fungicides with others from different groups that control the same pathogens.
  • Tank mix fungicides that have a high risk of developing insensitivity with other fungicides from a different group.
  • Do not apply more than the maximum number of applications listed on the label. Avoid consecutive sprays of the same fungicide, or other fungicides in the same group, in a season. Fungicides belonging to the strobilurin group should not be applied more than twice a season in the same field. Note: Western Canada has reported the development of resistance of several fungal pathogens to the strobilurin group of fungicides.
  • Fungicide application should be based on an integrated pest management (IPM) program that includes scouting and accurate recording related to pesticide use and crop rotation. An IPM program also considers cultural, biological, and other chemical control.
  • Monitor treated fungal populations for signs of fungicide insensitivity. If disease continues to progress after treatment, do not reapply the same product with a higher rate.
  • If you observe fungicide insensitivity, discontinue use of the product and switch to another fungicide with a different mode of action.

Top 3 Diseases Impacting Field Peas

  1. Root Rot Diseases (Seed Rot, Seedling Blight, Root Rot, Rhizoctonia Root Rot, Fusarium Root Rot, Aphanomyces Root Rot), for a full description go to Seed or Soil Borne Diseases.
  2. Ascochyta/Mycosphaerella Blight – for a full description go to Foliar Diseases.
  3. Sclerotinia Stem Rot – for a full description go to Foliar Diseases.

Watch the VideoAscochyta in Peas