July 5, 2023

• Crop Update
  • Grasshoppers in Soybeans and Pulses →
  • Fungicide Decisions in Peas →
  • Scouting for Pea Aphids →
  • Early Pea Leaf Weevil Survey Results →
  • Growth Staging Guides →
  • Scouting Calendars →
• Hail Damage in Soybeans
• Assess Soybean Nodulation →
• Evaluating Dry Bean Nodulation
• Soybean Fungicide Decisions
• Dry Bean Fungicide Decisions →
• Regional Variety Trials Update

Crop Update

• Soybeans range from V5 to R2 (open flowers on one of the uppermost 4 nodes).
  • Ensure inoculation strategies were successful ahead of pod development and filling stages by checking up on soybean nodulation. Assess soybean nodulation →
  • Hail has hit several soybean fields. At R1 stages, yield loss depends on the amount of defoliation and stem nodes removed. More information below.
• Field peas range from R1 (flower buds) to R3 (flat pod).
  • Symptoms of Mycosphaerella (Ascochyta) blight are more common to find in the lower pea canopy. Fungicide applications are on-going. Fungicide Decisions in Peas →
  • Bacterial blight is also present in some fields, following storm damage.
  • Pea aphids are present at low levels in some pea fields. Scouting for Pea Aphids →
  • When digging up pea roots in western Manitoba to check nodulation, you may find pea leaf weevil larvae and pupae in the soil. This pest feeds on root nodules below-ground. High numbers have been noted in northwestern Manitoba and in areas north of #1 Hwy in western Manitoba.
• Dry beans range from V4 to R1.
  • In fields with a history of dry beans, active root nodules are present in some fields. Dig up your dry bean roots to check for nodulation.
  • Potato leaf hoppers are a pest of dry beans. Triangular brown areas at the tips of leaves or dwarfed, crinkled leaves are a sign of hopper burn. Examine the undersides of leaves to look for potato leaf hoppers and determine the number per trifoliate on average. At V4, the economic threshold is 1 leaf hopper/trifoliate and at R1 is it 2 leaf hoppers/trifoliate.
  • Fungicide Options
• Faba beans range from R1 to R4 (flat pod).
  • Blister beetles are present in some fields, but defoliation has been minimal.
  • Pea aphid thresholds for faba beans are 24-50 aphids per main branch. This gives a seven-day lead time before populations reach economic injury levels (96-142 aphids/main branch).
• Assessing grasshopper damage in soybeans and pulses →
  • Defoliation thresholds:
    • Soybeans: 30% defoliation pre-bloom; 15% defoliation from R1 (flowering) to R5 (beginning seed).
    • Dry beans: 35% defoliation pre-bloom; 15% defoliation after R1 (flowering).
    • Peas are not a preferred food source for grasshoppers. Infestations of 10/m² (1/ft²) do not cause economic losses in peas.

Hail Damage in Soybeans

Thunderstorms and hail have been common in Manitoba this year. How much yield loss can you expect once your soybeans have been hit by hail?

From 2015 to 2018, research was conducted to evaluate the effects of simulated hail damage on soybean yield and days to maturity at Portage and Minto, MB. Soybeans at the full pod (R4) and early seed fill (R5) growth stages were the most sensitive to leaf loss and stem breakage.

To estimate yield loss following hail:

1. Assess plant stand loss, if any. Plants can regrow from axillary buds on remaining stem nodes.
2. Estimate percent stem breakage. At R1, plants often have 5 nodes (4 trifoliate nodes and one unifoliate node). Stem breakage = nodes removed / total nodes the crop had before hail.
3. Estimate percent defoliation of remaining plant tissue. Is it closer to one-third, two-thirds or  100% of leaf material lost?
4. Using the chart below, add the loss percentages of defoliation and stem breakage together to estimate yield loss.

Days to maturity may also be impacted by hail damage. At R1, 100% defoliation caused a 4-day delay in maturity, while other defoliation severity levels did not impact maturity. At R1-R2, 60-80% node removal resulted in a 4 to 6-day delay in maturity, while 20-40% node removal matured 2 to 3 days later than plants with no damage.

• Soybean Yield Response to Defoliation and Node Removal – Research Reports from the Soybeans and Pulse Agronomy Lab →

Assessing Soybean Nodulation

Soybeans are flowering right now, and this is a great time to dig up roots and check on your nodulation. Nitrogen requirements peak during pod fill, so assessing nodulation now at flowering will give you enough lead time to come in with a rescue treatment if one is needed.

• Dig up 5-10 plants from 2 or 3 different areas of the field at R1-2 (flowering).
• If soils are clumping, soak roots in a pail of water to loosen up the soil since nodules can easily be stripped from the roots.
• Count the number of nodules per plant. Research has shown that soybeans need 10 nodules per plant, regardless of size, to reach 90% of maximum yield.
• Cut open a few nodules to check that they are pink-ish red inside, meaning they are actively fixing nitrogen.
• Note the location of the nodules – successful seed-applied inoculant will result in nodules clustered around the main taproot near the crown of the plant, while in-furrow applications may result on nodules further from the crown. Naturalized Bradyrhizobia populations may form nodules further down lateral roots.

If insufficient nodulation is found and the crop appears pale green to yellow, a rescue application may be necessary at R2 (full flower) to R3 (early pod). Broadcast granular N or direct liquid N below the crop canopy to avoid leaf burn. Apply at a rate of 50 lbs N/ac.

• More Information on Assessing Soybean Nodulation →

Evaluating Dry Bean Nodulation

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). As N fertilizer rate applied increased, nodulation decreased.

This year, a new, $6.6 million dollar research project has started through the Genome Prairie program. As part of this project, researchers at the University of Manitoba and Queen’s University are aiming to develop an effective inoculant for dry beans. Currently, soils are being collected by MPSG’s agronomists from fields in Manitoba that have a history of dry bean crops. To contribute fields to this research, contact Laura, MPSG Production Specialist – West (204-751-0538; laura@manitobapulse.ca) or Gerry, MPSG Production Specialist – East (204-751-0737; gerry@manitobapulse.ca).

Soybean Diseases and Fungicide Decisions

• Foliar diseases infecting soybeans in Manitoba typically occur at low severity levels and are not expected to impact yield most years. These include bacterial blight, downy mildew and Septoria brown spot.
• Stem diseases generally have a greater impact on yield.
  • White mould: infections begin at nodes along the main stem. Wilted plants may be spotted from afar, within a humid canopy may find white mycelial growth and black sclerotia bodies later in the season. This disease is the main target of fungicide applications. Cool, wet conditions throughout July and August favour white mould. For every 10% increase in the percent of plants infected with white mould, 2-5 bu/ac of yield are lost in soybeans. Early infections are the most damaging.
  • Northern stem canker: small, reddish-brown lesions at the base of a branch or petiole in the lower third of the canopy after flowering. Lesions expand to form sunken cankers with reddish margins. May be confused with Phytophthora root and stem rot.
  • Phytophthora root and stem rot: late infection appears as a chocolate brown lesion on the stem that extends upwards from the soil line. If roots are rotten, suspect PRR. If roots appear healthy, northern stem canker may be suspected.
  • Pod and stem blight: distinct lines of raised, black dots on infected stems and pods.
  • Anthracnose: reddish-brown, irregularly-shaped blotches on leaves and stems. Black fungal bodies develop in these blotches later in the season.
• From 2014 to 2020, 66 on-farm trials have compared a single application of fungicide at flowering to none in soybeans through the On-Farm Network. The main disease target to manage has been white mould. In these trials, fungicide improved soybean yield 15% of the time when compared to no application. Though rarely occurring at severe levels, when conditions are optimal for white mould to develop, soybean yield will be protected with a fungicide application. Watch the results summary video of these trials: Soybean Diseases and Fungicide Applications (13 minutes) →

Dry Bean Fungicide Decisions

• Foliar fungicides to control white mould (Sclerotinia) are preventative, meaning they are applied before disease symptoms are visible. 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.
• In 2022, white mould was found in 56% of dry bean crops surveyed. Overall, infected leaf area by white mould was 6.5%. From 2018 to 2021, the percent of fields infected with white mould was below 30%. More moisture in 2022 contributed to an increase in this disease.
• Whether fungicide applications will be warranted this season is dependent on yield potential of the crop, the amount of precipitation received in July around flowering and if recent, previous broadleaf crops in the field or vicinity have had high white mould (Sclerotinia) levels, which will contribute more spore-producing sclerotia bodies to the area.
• The Fungicide Decision Worksheet for Managing White Mould in Dry Beans (also available in MPSG’s Bean App) can help determine the risk of disease development, based on environmental and agronomic factors, and aid in the decision of whether or not to apply a fungicide.
• According to recent NDSU research, the best predictors of optimum fungicide application timing were percent canopy closure and the percent of plants with one or more initial pods (pin-bean pods when first pods are 0.5-1″ long).
  • Pinto beans: When the canopy was at or near closure (average ≥ 95% of the ground covered) when the first pin-shaped pods were developing, white mold management and pinto bean yield were optimized when fungicides were applied when approx. 15% of plants had initial pin-shaped pods. When the canopy was open (average < 95% of the ground covered) when the first pin-shaped pods were developing, white mold management and dry bean yield were optimized when fungicide applications were delayed until 50% of the plants had initial pin-shaped pods. The growth stage which optimized fungicide performance was the same irrespective of whether one fungicide application or two sequential applications were made.
  • Black beans and navy beans: When the canopy was open (average < 95% closure) when the first pin-shaped pods were developing, the response to fungicides was very similar irrespective of whether applications were made at the first appearance of pin-shaped pods or delayed until 30-50% of plants had initial pods. However, yield gains in individual studies were highly variable when fungicide applications were made after 20% of plants had initial pods, indicating that making applications when more than 20% of plants had initial pods is only optimal when conditions do not favor infection by the Sclerotinia/white mould pathogen.

Regional Variety Trials Update

Soybean, pea, dry bean and faba bean varieties are tested each year at multiple locations across Manitoba. The purpose of this testing is to provide independent, unbiased data to help farmers choose the best varieties suited to their farms. Results from previous years can be found here →

Soybeans 2023

• 64 herbicide-tolerant soybean varieties are being tested at long-season sites (St. Adolphe, Carman, Portage and Morris)
• 56 herbicide-tolerant soybean varieties are being tested at western sites (Hamiota, Souris, Cypress River, Melita and Dauphin)
• 44 herbicide-tolerant soybean varieties are being tested at short-season eastern sites (Stonewall, Arborg and Beausejour)
• 15 herbicide-tolerant soybean varieties were entered into the first-year entry trials (tested at Carman, Hamiota, Melita, Morris, Souris and St. Adolphe)
• 33 conventional soybean varieties are being tested at long-season sites (St. Adolphe, Carman, Portage and Morris) and 26 conventional varieties are being tested at short-season eastern sites (Stonewall, Arborg, Beausejour) and 9 conventional varieties at Melita and Swan River
• Of the varieties submitted to these regional trials, 92 have been sent for independent Phytophthora root rot tolerance testing (71% of varieties submitted)
• Soybean varieties are also grown on an IDC-prone site near Winnipeg to assess their tolerance to IDC

Pulses 2023

• 45 dry bean varieties are being tested on wide rows at Morden, Carman, Winkler and Portage. Market classes include pinto, black, navy, light red kidney, dark red kidney, white kidney, cranberry and great northern beans
• 21 pinto, black and navy bean varieties are being tested on narrow rows at Morden, Portage, Melita and Souris and 9 pinto and black varieties at Swan River
• 18 pea varieties are being tested through MCVET at Morden, Stonewall, Roblin, Melita, Swan River, Cypress River, Carberry, Arborg, Souris and Hamiota
• 12 faba bean varieties are being tested at Dauphin, Morden and Swan River
• 8 lupin varieties are being tested at Melita and Carberry