Mid-season, The Bean Report

The Bean Report – June 21, 2023

JUNE 21, 2023

Crop Update

  • Soybeans range from V2 to V6, with some fields beginning to flower already. With the change in daylength this week, soybeans will be heading towards reproductive growth. If not seeing them already, expect to see flowers in the coming weeks.
    • Herbicide applications are ongoing to manage a second flush of weeds. Options for Volunteer Canola Control →
    • Hail has occurred in some areas, causing leaf tearing and some defoliation.
    • Symptoms of Iron Deficiency Chlorosis (IDC) have been present in fields with more moisture, interacting with calcium carbonates, soluble salts, and nitrates in the soil to limit iron uptake. If soybeans grow out of the symptoms by V5-V6, yield loss is expected to be minimal. IDC in Soybeans →
    • Grasshoppers have been found causing defoliation on field edges. Pre-flowering, the threshold for defoliation is 30% in soybeans and dry beans. From flowering to pod fill, the threshold is lower at 15% defoliation. As of June 11, grasshopper egg hatch was predicted by the Prairie Pest Monitoring Network as mostly complete. Control of grasshoppers is most effective once hatch is complete and nymphs are still concentrated in hatch areas (field edges). Edge sprays are often sufficient and the lowest label rates are needed when they are small. Grasshoppers in Soybeans and Pulses →
  • Field peas range from V9 (9 true leaf nodes) to R1 (flower buds) , with a few open flowers in some earlier-seeded fields.
    • In areas that have received more moisture, peas are yellowing around low spots and drains due to root rots.
    • Early symptoms of Mycosphaerella blight can be found in the lower canopy of some fields. Bacterial blight has also been found infecting pea leaves and stems. Symptoms of these two disease can be quite similar, which can be confusing when making fungicide decisions. Find photos to tell them apart here →
    • The spring 2023 pea leaf weevil survey has wrapped up. Early PLW Survey Results → Pea leaf weevil populations were found to be greater than last year in western Manitoba and the pest has been confirmed further east into central Manitoba. Root nodules with signs of larvae feeding damage may be found when digging up plants.
  • Dry beans range from V1 to V4.
    • Herbicide applications are ongoing. Dry Bean Herbicide Options (2023) →
    • Hail storms moving through the southwest has caused defoliation and stem breakage in some black bean fields. In the case of stem breakage, plants are regrowing from axillary buds.
  • Faba beans range from V9 to V11.
    • Blister beetles may be found in some faba fields. While some defoliation is caused by blister beetles, it is not usually economical to control them. The grey or black Epicauta blister beetles eat grasshopper eggs.

Scouting Peas at Flowering: Fungicide Decisions, Aphids and Nodules

Foliar Fungicide Decision Making in Peas →

  • Mycosphaerella (ascochyta) blight is the main disease target of foliar fungicides in peas.
    Mycosphaerella blight disease symptoms (small dark freckles) on lower pea leaves.

    This disease 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.

  • 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, avoid applying a group 11 product alone.
  • Due to recent hailstorms, bacterial blight is showing up in pea fields as well. This disease is commonly confused with Mycosphaerella blight and bacterial blight will not be controlled by a fungicide. Find photos and descriptions on how to tell Mycosphaerella Blight vs. Bacterial Blight →

Pea Aphids →

  • Scout for pea aphids when 50-75% of the field is in early flower in late June to early July.

    Check the closed uppermost stipule leaves for pea aphids.
  • 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.
  • 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.
  • Scouting for Pea Aphids Video (2 minutes) →
  • Insecticide Options for Pea Aphids (2023) →

Nodulation in Peas →

  • Assess pea nodulation at flowering (R1-2).
  • Since pea nodules are indeterminate and branch as they grow, a scoring card is used to assess nodulation.
  • Select 5-10 plants from 2-3 different areas of the field.
  • Visually assess above-ground growth and vigour.
  • Using a shovel, carefully dig up plant roots. If soils are heavier, roots may need to be soaked before rating.
  • Count the number of nodule clusters and note their location (at the crown, near the seed, or on the lateral roots). Break open a few nodules to determine if they are pink inside, indicating active N fixation.

Iron Deficiency Chlorosis in Soybeans

Up to V1, soybean cotyledons supply stored iron to the plant. Once that source is depleted, plants need to acidify their root zone to access iron in a plant-available form. Excess moisture, calcium carbonates, soluble salts and nitrates can all impact this.

If chlorosis is present early on and plants recover by the V5 to V6 stages, yield loss will be minimal. If symptoms persist beyond these stages, expect more significant yield loss. Research conducted in Manitoba has shown that for each 0.1 unit increase in IDC score, soybean yield is estimated to be reduced by 2.2 bu/ac, on average (range: 1.5 – 2.8 bu/ac).

Research: Iron Deficiency Chlorosis – Kristen MacMillan, MPSG’s Agronomist-in-Residence, Soybean and Pulse Agronomy Lab, University of Manitoba (2017-2022).

On-Farm Network Seeding Rate Trials

In 2023, the On-Farm Network has 13 soybean seeding rate trials established and two pea seeding rate trials. Early-season plant counts at these trials have been on-going.

Soybean Seeding Rates

Soybean seeding rate trials have been ongoing in the On-Farm Network since 2012. It’s the most popular trial type, with more than 100 trials conducted so far. With these trials, we compare the farmers typical seeding rate vs. 30,000 seeds/ac higher and lower to evaluate the effect on yield. One of the key questions we’re looking to answer with these trials if if we can reduce our soybean seeding rates without impacting agronomics and yield to lower input costs?

In 2023, trials are comparing anywhere from 120,000 seeds/ac to 220,000 seeds/ac, depending on the trial. Early-season plant counts have shown an average of 80% establishment from the seeding rate, which is the same as the long-term average for early-season percent establishment in these trials. Typically, as seeding rate increases, fewer of the seeds put in the ground establish as a living plant (lower percent establishment) – that trend has held consistent again this year at the majority of trials.

Pea Seeding Rates

Two pea seeding rate trials have been established this year in the On-Farm Network near Notre Dame and Dauphin. Early-season plant stand counts show these trials are comparing a living plant stand of 4.2-5.1 plants/sqft and 5.4-7.1 plants/sqft, respectively. The recommended target plant stand in peas is 7-8 plants per square foot. Like with soybean seeding rate trials, lower pea seeding rates have typically resulted in a greater percentage of the pea seed establishing. Since these trials started in 2021, there has not been a significant yield response to different pea seeding rates to-date.