Mid-season, The Bean Report

The Bean Report – July 6, 2022

JULY 6, 2022

Listen to the Bean Report:

Crop Update

  • Soybeans are at V1 to V4 stages and will be starting to flower soon with the change in day length. IDC symptoms have started to show up in some fields, but many fields remain symptom-free.
    • Many fields were rolled post emergence due to conditions not being suitable after seeding. Soybeans that were rolled post emergence are rebounding well.
    • Soybean aphids have been reported in the central region. Monitor for this pest from R1 to R5. In non-outbreak years, soybean aphid populations are often suppressed by natural enemies like ladybeetles and their larvae, hoverfly larvae, green lacewings, parasitic wasps and more.
  • Field peas range from 6 to 12 true leaf nodes, some at R1 (flower bud) with a few open blooms scattered throughout the field to R3 flat pod stage. As pea flowering advances this week in many fields, start looking for Mycosphaerella blight in the lower canopy, check plant tips for pea aphids and dig up roots to assess nodulation.
  • Dry beans range from V1 to V4. Ahead of dry bean flowering, Dr. Michael Wunsch, NDSU, has summarized their research on optimizing fungicide application timing for improved management of white mould in different bean market classes.
  • Faba beans range from 7 true leaf nodes to beginning bloom. As with peas, flowering is the best time to check nodulation and to start looking for pea aphids in faba beans.

Scouting Update

  • Strong winds and hail have been reported in some areas of the province, resulting in leaf tearing and stem breakage. In some areas, plants are regrowing while in others, plant stands have been reduced. To learn more about defoliation effects on soybean yield, read about the Soybean & Pulse Agronomy Research lab results here.
  • Seedling diseases and root rots have impacted plant stands in areas of the field that have remained saturated.
  • Grasshopper nymphs have been feeding at field edges. At vegetative stages, the threshold for control in soybeans is greater than 30% defoliation and for dry beans is 35% defoliation. Research from Ontario has also indicated that soybeans can tolerate up to 50% defoliation at early V-stages. Border or edge sprays at these stages are often enough for control. Find more information here.
  • Blister beetle adults can be found in some fields. Epicauta blister beetle larvae feed on grasshopper eggs in the spring. As adults, they can occur in small patches in the field but often do not feed in the field for very long before moving on. While they cause some defoliation, it is usually not economical to control blister beetles. There are grey and black Epicauta blister beetles and shiny metallic Nutall’s blister beetles.
  • Pea aphids have been found migrating into pea and faba fields. Unlike soybean aphids, pea aphids overwinter here. Scout peas around flowering and podding to monitor for this insect. More information on this pest below.
  • With a challenging spring, some fields are still in need of rolling. At this point in the growing season, roll only if you have stones that will absolutely be a problem at harvest. The ideal time to roll post-emergence is at V1 for soybeans and V2-3 for peas. If rolling beyond these stages, use caution – damage to the crop is likely to occur. Wait for a hot day (>25°C) when the field is dry. Check how flexible plants are and check frequently to assess breakage. Peas pod higher than soybeans, but often lodge. Weigh the pros against the cons for your fields and proceed with caution.
  • Iron Deficiency Chlorosis (IDC) is showing up in soybean fields where new trifoliate leaves are lime green to yellow.
    • After V1, soybean roots need to acidify their root zone to access iron available in the soil. Excess soil moisture, calcium carbonates, soluble salts and/or high nitrate levels can hinder iron uptake into the plant and increase the risk of IDC. If plants recover by V6, yield loss will be minimal.
    • In-season management options for IDC have not been very effective, but you can accurately diagnose the problem and adjust management strategies for future years by selecting an IDC tolerant variety.

Pea Foliar Fungicide Decision Making

  • Mycosphaerella (ascochyta) is the main disease target of foliar fungicides. It infects most pea crops at some severity level each year. The impact on yield is determined by how early the disease sets in and how quickly it progresses into the upper canopy. Early infections during R2 to R3 cause the most damage.
    • Fungicides may also provide control of suppression of white mould, downy mildew, anthracnose and other diseases depending on the product.
  • Scout for symptoms from V10 (tenth true leaf node) to R2 (beginning bloom). Use the Fungicide Decision Worksheet for Managing Mycosphaerella Blight in Field Peas to assess if a fungicide application may be beneficial in your field.
  • Apply foliar fungicides at R2 when on flower is open on most plants across the field. If warm, humid weather persists and the disease progresses up the canopy, consider a second fungicide application 10 to 14 days later using a different mode of action.
    • It is likely that the Mycosphaerella pathogen is resistant to group 11 strobilurin fungicides. If applying a foliar fungicide to manage Mycosphaerella blight, select a product that has more fungicide groups than a group 11 alone.
  • Find more information about the Mycosphaerella/Ascochyta complex in peas here.
  • Find more information about making fungicide decisions in peas here along with helpful photos comparing Mycosphaerella blight and bacterial blight.

Scouting for Pea Aphids

  • Begin monitoring for pea aphids when 50-75% of the pea or faba bean crop is in early flower.
  • Check five plant tips (top 8 inches) or conduct 10 sweeps at four locations within the field. Assess populations in different areas of the field, including field edges. Populations will likely be higher at field edges.
  • The economic threshold for peas is 2-3 aphids/plant tip or 90-120 aphids/10 sweeps. At greater pea prices, the economic threshold for control may be reached earlier. On average, 2 aphids per plant tip (10 aphids/sweep) has been equivalent to 5% yield loss when the crop is at 25% flower. Find the aphid number vs. pea yield loss table here.
  • If the threshold is reached, insecticide applications should be made at the early pod stage (when 50% of plants have produced young pods). Pod formation and elongation stages are the most sensitive to aphid feeding.
  • Natural enemies may reduce pea aphid populations. Scout for lady beetles and their larvae, hoverfly larvae, minute pirate bugs, damsel bugs, parasitic wasps that leave behind aphid mummies and fungal diseases that infect aphids.

Assessing Field Pea Nodulation

The best time to assess nodulation in pea fields is at flowering (R1-2) to capture peak nodulation.  Peas will begin to form root nodules as early as 14 days after emergence. Nodulation failure can occur due to high soil nitrate levels, inoculant application issues or root rot.

Peas have indeterminate nodules that have a cylindrical shape that tends to branch out as they develop. This branching makes pea nodules more difficult to count than determinate root nodules like we have with soybeans.. As a result, a scoring system is used to assess nodulation.

  • Select 5-10 plants from 2-3 different areas that are representative of the field.
  • Use a shovel to gently dig out each root system. Carefully wash the roots in a pail of water to remove soil, as nodules can easily be stripped from the lateral roots during extraction.
  • Assess overall plant growth and vigour, count the number of nodule clusters per plant and note the position of nodule clusters on the plant, according to the worksheet below.
  • Cut a few nodules open to assess the colour. If the nodules are pinkish-red inside, they are actively fixing N. Brown, white or green nodules are considered ineffective.
  • Conduct nodule assessments on additional plants if there is a wide variation across locations and plants.











Post-Emergent Herbicide Options in Soybeans for Volunteer Canola Control

Read more about research conducted in Manitoba on managing volunteer canola in soybeans in the following Science Edition articles:

  1. Action Thresholds for Volunteer Canola in Soybeans
  2. Managing the Volunteer Canola Seedbank after Harvest
  3. Herbicide Options for Volunteer Canola in Xtend Soybeans
  4. Herbicide Options for Volunteer Canola in Enlist Soybeans
  5. Making Soybeans More Competitive with Volunteer Canola

Upcoming Events

  • July 5 to 8: Crop Diagnostic School at Carman. CDS Farmer Day on July 8 is free for famer members of MCA. To register for Farmer Day, please email mbcropschool@gmail.com.
  • July 20: Westman Agricultural Diversification Organization (WADO) Field Day at Melita.
  • July 26: Prairies East Sustainable Agriculture Initiative Inc. (PESAI) Field Day at Arborg.
  • July 26: Combine College at Dauphin.
  • July 27: Parkland Crop Diversification Foundation (PCDF) Field Day at Roblin.
  • July 28: Combine College at Portage la Prairie.
  • August 3: MPSG Dry Bean Tour at AAFC-Morden.
  • August 9: Canada-Manitoba Crop Diversification Centre (CMCDC) Field Day at Carberry.