Mid-season, The Bean Report

The Bean Report – July 17, 2024

JULY 17, 2024

Listen to the Bean Report:

Crop Update

  • Soybeans range from R1 (beginning bloom) to R2 (full flower). Several late-seeded fields are still at vegetative growth stages and are expected to form flower buds once they reach V3.
    • Weed control applications have been challenging this year between saturated soil conditions and high winds. Narrow-row soybeans have been better able to compete with existing weed pressure.
    • Assess nodulation in soybeans at flowering. Soybean nitrogen requirements peak during pod fill, so assess nodulation now to provide enough lead time if a rescue treatment is needed. Soybeans need at least 10 nodules per plant to support maximum yield.  Assess Soybean Nodulation →
    • Several fields are re-growing from previous hail damage. Evaluating Hail Damage and Recovery in Soybeans →
    • Soybean aphids have blown in on southern winds. Populations remain low in most fields and natural enemies like ladybeetles and green lacewing larvae are able to manage populations. Managing Soybean Aphids →
    • Fungicide applications have begun in fields that have higher white mould risk. Fungicide Options in Soybeans →
  • Field peas range from R2.5 (full bloom) to R3 (flat pod) with seeds filling.
    • Considering second fungicide applications → scout to see if disease symptoms have progressed up the plant into the mid or upper canopy and to check humidity in the crop canopy. If these conditions are occurring and rain is in the forecast, a second application may be warranted. Use the fungicide decision worksheet to assess risk → In On-Farm Network trials, a second application of fungicide improved pea yield 44% of the time, improving yield by 5.1 bu/ac on average. When humid conditions persist, there is often a return on investment to a second application of fungicide. Fungicide Options in Field Peas →
    • Pea aphids have been increasing in numbers in several pea fields, with insecticide applications occurring in some areas. Economic thresholds for pea aphids are 2-3 aphids/plant tip or 9-12 aphids/sweep on average. If thresholds are reached, applications at early pod (when 50% of plants have produced young pods) have been shown to provide the best yield protection. Foliar Insecticide Options for Pea Aphids →
  • Dry beans range from V3 to R2 (pin bean, early podding) stages.
  • Faba beans range from R3 (50% bloom) to R4 (flat pod).
    • Lygus bugs cause seed pitting in faba beans from feeding damage. Sweep net fabas during podding stages for lygus bugs. A nominal threshold has been proposed of 5-10 lygus bugs/10 sweeps at early R4 (flat pod) to keep damage below 15%. Lygus bugs in faba beans video (1 min 30 sec) →
    • Pea aphid thresholds in faba beans are higher than in peas. The action threshold of 34-50 aphids/main branch gives a 7-day lead time before injury levels are reached (96-142/main branch). Include natural enemies such as lady beetles, hoverfly larvae and others when considering management decisions. Faba bean yields are improved by pollinators in the field, so use practices that minimize effects to pollinator species.
    • Fungicide applications are on-going. Chocolate spot is the main disease target in faba beans. Chocolate spot in faba beans →
Soybeans at R2 (full flower).
Soybeans following hail damage (R1-2).
Peas with flat pods (R3).
Faba beans blooming (R3).
Faba bean root nodules.

Fungicide Decision Making in Dry Beans

White mould (Sclerotinia) is the main disease target of fungicide applications in dry beans. This application is preventative, meaning fungicides are applied before disease symptoms are visible and only protect the tissues that they are applied on. Fungicides can also offer control or suppression of anthracnose, powdery mildew and rust, depending on the product. However, these diseases are less frequent and less severe in Manitoba-grown dry beans. Dry Bean Fungicide Options →

The R2 beginning pod stage (first pin nodes are 0.5 to 1″ long ) and 100% of plants have an open blossom  is the best time to apply a fungicide for effective white mould control.

White mould prevalence has been variable the past four years (Table 1) and has been affected by each year’s environmental conditions and whether they were supportive of disease development.

Factors that Contribute to White Mould Disease Development at Flowering:

  • Risk of disease development if warm, humid conditions persist around flowering
    • Optimal temperatures: 15-25 °C
    • Humidity: 1 – 2 inches of rain within 1 – 2 weeks of flowering
  • Risk greater with thick dense canopies
    • (high plant populations in narrow rows with more N with lush, thick canopies)
  • Risk greater on fields in rotation with other susceptible crops (canola, soybeans, sunflowers, etc) and if the last broadleaf crop had heavy white mould infection

Table 1. White mould prevalence and severity in the dry bean disease survey from 2020 to 2023.

Disease

 Rating 2020 2021 2022 2023
White Mould

Prevalence (%)

 31 2.5 56

5
Severity (% infected leaf area) 3.1 0.3 6.5

2

To walk through the factors impacting disease development and to help determine the risk of white mould in your fields check out the  Fungicide Decision Worksheet for Managing White Mould in Dry Beans (also available in the Bean App).

If warm, humid conditions persist throughout flowering and pod development, consider a second fungicide application 7 to 14 days later.

From 2016 to 2023, 18 On-Farm Network trials have compared a single application of fungicide vs. none in dry beans and one trial has compared two applications vs. one. July rainfall was at or above normal at 4 out of 18 single vs. none trials, otherwise trial fields were drier than normal. In these trials, a fungicide improved yield 11% of the time when compared to no application, and yields were improved by 165 – 175 lbs/acre.

Dry bean fungicide trials are on going this year, stay tuned for results. Or check out previous year’s results.

Disease Highlight: White Mould (Sclerotinia)

White mould (Sclerotinia sclerotiorum) has a wide host range, infecting most broadleaf crops including canola, sunflowers, soybeans and dry beans. In wet years conducive for disease development, white mould can have major impacts on yield.

Soybeans are typically more resistant to white mould infection than dry beans, mostly due to their upright plant architecture allowing more airflow in the crop canopy. Depending on variety, dry bean plant architecture is typically more compact with several branches, trapping more humidity and limiting airflow.

Early infections are the most damaging to yield. In soybeans, for every 10% increase in white mold incidence in a field, 2-5 bu/ac may be lost.

Symptoms of white mould include bleached stems and wilted plants. White, fluffy mycelial growth may be present with ample humidity in the crop canopy. When you break open stems, you’ll find hard black sclerotia bodies – these are the resting bodies that survive in crop residues and the soil, perpetuating the disease cycle.

Wilted plants in a soybean canopy caused by white mould.
Bleached soybean stem from white mould infection.
Bleached soybean stem from white mould infection with white growths.
Breaking open bleached soybean stems to find hard, black sclerotia resting bodies.
White mould infecting soybean pods.
White mould infecting navy beans with wilted leaves, soggy plant growth and bleached plant parts.
Bleached navy bean branch with infected pods.

Fungicides for white mould are preventative, meaning they must be applied before symptoms are visible and fungicide decisions need to be made by evaluating risk in the field.

Consider weather conditions and the density of the plant canopy – how much humidity is trapped in that plant canopy, allowing disease to flourish? In dry beans, high plant populations and higher nitrogen rates applied have had the greatest impact on white mould development. For soybeans, higher plant populations on narrower rows have resulted in more dense canopies.

Also consider previous canola, sunflower or broadleaf crops in that field – did you notice white mould infections? Typically sclerotia survive in the soil for up to five years. We’ve had drier crop conditions the last few years, so the amount of disease present in the soil may be lower in some fields, reducing risk.

Evaluating Dry Bean Nodulation

Pinto bean root nodules from a field near Souris on June 27, 2023.

Do you check nodulation in your dry bean crops? You might be surprised by what you find!

Dry beans are fertilized with nitrogen like a non-legume crop since they’re poor nitrogen fixers. However, poor nitrogen fixers are still fixing some nitrogen. In fields with a history of dry beans, we have observed plenty of active nodules on roots. Research has not been done to relate nodule number to yield in dry beans, but rating nodulation can provide insight on whether or not you should consider biological N fixation when making nitrogen management decisions.

  • Dig up roots during flowering to early podding stages.
  • Count the number of nodules present, using the following rating scale:
    • 0 = no nodules
    • 1  (poor) = < 5 nodules/plant
    • 2 (moderate) = 6 – 10
    • 3 (good) = 11- 20
    • 4 (excellent) = >20
  • Break open the nodules to check colour. Pink nodules are active, while green, brown or white nodules are not fixing nitrogen.

In MPSG’s On-Farm Network dry bean nitrogen trials, fields have not been inoculated, yet often have good to excellent nodulation (rating 3 to 4 out of 4). As N fertilizer rate applied increased, nodulation in the field decreased.

More information on digging up those dry bean roots! →

Crop Diagnostic School Recap: Root Rots

MPSG agronomists participated at Crop Diagnostic School this year, sharing more information on key root rots.

MPSG agronomists participated in the disease session of Crop Diagnostic School this year, highlighting two nefarious root rots: Phytophthora root and stem rot in soybeans and Aphanomyces root rot in peas.

‘Phytophthora’ is an unwieldy name to grasp. Its name is Greek, with ‘Phyto’ meaning ‘plant’ and ‘phthora’ meaning ‘destruction, decay, ruin or perish’. Put these together and we get the Plant Destroyer, Phytophthora root and stem rot. ‘Aphanomyces’ doesn’t have a similar fun break-down, but we can say we’re not A-fan-o’-mycetes. It’s cheesy, but memorable.

Both of these diseases have a few things in common, since they’re both oomycetes, or ‘water moulds’. Water being a key piece here, as both of these diseases require soil moisture for a portion of their life cycle so they can swim to infect plant roots. Since we’ve had drier years, they’ve been less common to observe in the field, but with a return of more moisture this season, we anticipate these being a larger concern. Both of these diseases are also long-lived in the soil as resting oospores, surviving 5 to 10 or more years.

These two root diseases are not alone in our soil, and will typically co-infect with Fusarium root rots. In annual disease surveys, we typically find some level of Fusarium root rot in every single soybean and pea field we survey. Keep those Fusarium root rots in mind as you consider root rot management of Phytophthora and Aphanomyces.

For Crop Diagnostic School, we put together a handy take-home covering the important points of Phytophthora and Aphanomyces root rots. You can check them out here for the full story:

Crop Management Field Tour – July 23, 2024

This farmer-focused tour, running from 8:30 a.m. to 1:oo p.m., will feature sessions on:

  • The impact of residue management on weed populations and soil moisture
  • Management of soil compaction
  • Soybean establishment, seeding depth and rolling
  • Nitrogen management for canola: split N and EEFs
  • Canola establishment with planter vs. drill

Register Today!