Early season, The Bean Report

The Bean Report – June 5, 2024

JUNE 5, 2024

Listen to the Bean Report:

Crop & Seeding Update 

Seeding and Field Conditions

  • Field pea seeding is close to finished, with seeding still underway for soybeans and dry beans. There is a wider range of seeding dates this year with more variability in crop staging among fields.
  • MASC Seeding Deadlines:
    • For soybeans, June 8 is the last day for full insurance coverage for soybean area 1, with extended coverage offered from June 9 to 13. June 9 will be the last day for extended coverage for soybean areas 2 and 3.
    • For dry edible beans, June 10 is the last day for full coverage in dry bean area 1, with extended coverage from June 11 to 15. June 6 is the last day for full coverage in dry bean areas 2 and 3, with extended coverage from June 7 –  June 11.
    • For field peas, June 15 is the last day for full coverage, with extended coverage running from June 16 to 20.
  • For most of the province, accumulated rain over the month of May was more than 150% of normal. This map shows the total accumulated precipitation for the month of May.

Crop and Pest Update

  • Soybeans are emerging (VE) to VC (unifoliate) stages.
    • Signs of seedling disease and emergence stress have been noted in a few fields, which is not surprising given the amount of accumulated moisture this spring.
    • Cutworm feeding has also been observed in some fields, mostly as a few bites taken out of cotyledons but below thresholds.
    • If you were unable to roll after seeding, post-emergent rolling is an option if rolling is needed. Target the V1 (first trifoliate) stage on a warm day during the hottest part of the day (~25°C).  Post-emergent rolling in soybeans →
  • Field peas range from VS to V6 (2 scale leaf nodes emerged to 6 true leaf nodes).
  • Dry beans are germinating with some fields beginning to emerge.
  • MPSG’s On-Farm Network field work is on-going, monitoring emergence and evaluating the impact of heavy moisture/snow, cold temperatures and strong winds on trials. Data collection is starting off with plant stand assessments, field scouting and drone imagery collection.

 

Weed Surveillance 

Weed surveys help us understand changes in weed populations both geographically and over time. These surveys represent a huge collaborative effort between Manitoba Agriculture and Agriculture and Agri-Food Canada (AAFC) research scientists.

The sixth weed abundance survey was conducted in Manitoba in 2022. Among 704 fields surveyed, 64 soybeans, 30 pea and 26 dry bean (specifically pinto bean) fields were surveyed. This was the first time that peas and dry beans have been included.

Of all crops surveyed, green foxtail remained the number one most abundant weed in Manitoba. It’s consistently held that spot since the 1970s. It was followed by wild buckwheat, volunteer canola, lambsquarters, and redroot pigweed. Compared to the previous survey, lambsquarters, redroot pigweed, yellow foxtail and kochia have been increasing over time, while wild oats and Canada thistle have decreased.

Volunteer canola was the most abundant weed in soybeans and peas, escaping control in 42% and 68% of fields, respectively, while redroot pigweed was the most common weed in pinto beans, infesting 35% of fields at the end of the season.

Herbicide Resistance

A subset of 155 fields was also surveyed for group (Gr) 1 and 2 herbicide-resistant weeds in 2022. All visible weeds with mature seeds were collected prior to harvest for assessment in the greenhouse.

Overall, 75% of fields surveyed had herbicide-resistant weeds in 2022. This is a continued increase compared to 68% in 2016 and 48% in 2008. The most common herbicide-resistant weed was wild oats, found in 37% of fields. All wild oats tested were resistant to Gr 1 and 82% were also resistant to Gr 2.

Kochia was the most common resistant broadleaf weed, occurring in 19% of fields overall. At this point, all kochia populations are assumed to be resistant to Gr 2 herbicides. Due to the timing of this survey in late August, there’s limited amount of mature kochia seed to be collected. As a result, this survey is unable to test for glyphosate or Gr 4 resistance in kochia.

New Gr 1 and 2 resistance issues of concern identified in this survey for further investigation include presumed Gr 1-resistant barnyardgrass, quackgrass and stinkgrass as well as presumed Gr 2-resistant quackgrass, spiny sowthistle, lambsquarters and Canada fleabane.

While the previous survey documents Gr 1 and 2 resistance, other cases of herbicide resistance are known to occur in Manitoba. We can also look to our neighbours, North Dakota and Saskatchewan, for other cases of herbicide resistance that may be in our future (included in grey).

Glyphosate-resistant kochia has been an ever-increasing problem since it was first reported. As of 2021, 74% of kochia surveyed across the Canadian prairies was confirmed to be resistant to glyphosate. In Manitoba, with our greater frequency of growing RR soybeans, corn and canola in rotation, we can expect that this number will quickly increase further.

Trails of glyphosate-resistant kochia through RR soybeans.

In terms of Gr 4-resistant kochia, that term is an over-generalization. Kochia populations in Manitoba have specifically been confirmed to be resistant to dicamba. For the most part, other Gr 4 herbicides like fluroxypyr can still have efficacy on these dicamba-resistant kochia populations. However, fluroxypyr-resistant kochia has been reported in the other Western provinces and may develop here. In 2018, only 1% of kochia populations in Manitoba had dicamba resistance.

On the horizon for kochia is Gr 14 resistance found in Saskatchewan (2021) and North Dakota (2022), as well as Gr 5 resistance which occurs throughout the United States. Of particular note in our soybean and pulse crops is the potential of losing Gr 14 efficacy – we rely fairly heavily on that mode of action due to limited in-crop herbicide options. Charles Geddes, AAFC–Lethbridge and his lab are investigating populations of Gr 14-resistant kochia further to assess if there’s broad cross-resistance to active ingredients within the Gr 14 PPO inhibitors.

Waterhemp is currently a Tier 1 noxious weed in Manitoba and plants must be destroyed if discovered. Of the populations that have popped up in Manitoba (Figure 1) and were sent for testing, resistance to Gr 2, 9 and 14 herbicides has been documented. These seeds are expected to have come into the province in many cases on Red River floodwaters, meaning we may also be seeing North Dakota’s waterhemp resistance to Gr 4 sometime soon.

If you’re not already, it’s time to start considering alternative, non-herbicidal methods of weed control on your farm and incorporating an integrated weed management strategy. We’re not spraying our way out of these resistance issues.

References
Leeson, J. et al. 2023. Prairie Weed Surveys Annual Report.
Geddes, C. et al. 2023. Manitoba survey of herbicide-resistant weeds in 2022.
Heap, I. 2024. Weedscience.org
Ikley et al. 2024. North Dakota Weed Control Guide

Scouting for Early Season Diseases

Spring has brought several rain showers this year, along with snow in western Manitoba. With excess moisture around plant establishment, seedling diseases and root rots should be part of crop scouting plans.

Check areas of patchy emergence, crop yellowing or wilting. Dig up seedlings to investigate further.

“Seedling disease” and “root rot” generally refer to the root rot complex. Diseases that make up the root rot complex differ slightly among crops. Fusarium spp., Pythium spp. and Rhizoctonia solani can infect all pulses and soybeans, Phytopthora sojae infects only soybeans and Aphanomyces euteiches mainly infects peas.

More information on scouting for root rots  →.

Root Diseases in Field Peas

Root rots in field peas are often caused by Fusarium and Aphanomyces pathogens. When Aphanomyces is present in a field, it often occurs together with Fusarium and root rot severity is much worse when they co-infect. They both flourish in warm soils. Aphanomyces thrives in saturated soils, while Fusarium may infect in dry or saturated soil conditions.

Favorable Conditions for Infection for Aphanomyces

Aphanomyces is a water mould, meaning that the oospores require moisture to release zoospores that swim to infect roots.

  • High spring rainfall provides favorable conditions for Aphanomyces.
  • Generally, infects in June and July when soils are warm and soil moisture is available.
  • Symptoms begin generally 2 to 3 weeks after a good rain.
  • May infect throughout the growing season.

Scouting and Root Rot Symptoms

Root rots most often infect in areas where water accumulates or ponds like low spots, drains and headlands. Above ground, peas infected with root rots will yellow from the base of the plant upwards.

Target these areas to understand root rot severity. Scout five areas of the field in a W or zigzag pattern. Dig up plants to evaluate root growth and assess if nodulation is occurring.

Scout around the low lying and compacted areas of the field. Move into the field away from infection areas (move up the slope, or away from compaction) to assess how far the root rot infection has spread in the field. Assess healthy areas of the field to get a whole picture of the field.

Although Aphanomyces and Fusarium have different symptoms, often they co-infect. It can be challenging to capture and distinguish which root rot is present. As a result, taking a plant or soil sample and sending it to a lab confirmation is recommended as they have very different impacts on rotation.

Sample Collection

Soil or plant samples may be submitted for DNA testing for confirmation. Soil samples can be taken at any time of year, collect samples from high-risk areas of the field like low spots, water runs or drainage areas.

Diagnostic labs may provide presence/absence confirmation or may provide an oospore estimate from soil samples (Table. 1).

Surveillance in Manitoba

Each year pea fields are surveyed for root, foliar and stem diseases. As part of this surveillance, soils are collected from pea fields and tested for Aphanomyces root rot at AAFC-Brandon (Table 2). In fields tested from 2019-2023, 82% were confirmed to have Aphanomyces and 99 % were confirmed to have Fusarium present in the soil, on average.

Insect and Disease Scouting Calendars for each crop type to help you know what to be scouting for:

Assessing Established Plant Stands

A lot of consideration goes into seeding rates to achieve a target plant population to reach maximum yield potential. Taking that next step to determine the established plant stands will help to ensure you reached the target plant population. As well, it provides you with information on seed survivability with your own equipment in this year’s conditions which helps to inform future seeding rate decisions.

Higher plant populations could mean increased yield potential, but also a greater risk of disease pressure. Lower plant populations mean more attention should be paid towards weed control. When soybean populations are so low that you’re considering replanting or topping up soybean stands, review information on soybean replanting decisions →

MPSG has a plant stand assessor tool to calculate plant populations:

This can be accessed in the MPSG Bean App or online through MPSG Online Plant Stand Assessor. Tips to conduct plant stand assessments →

  • Plant counts should be done when all plants have emerged.
  • Use the fixed area method to calculate plant populations if using a hoop or a square or the row length method if using a measuring tape or stick.
  • Enter your hoop diameter, area of square or length of row measured and the number of plants in that area.
  • Assess multiple spots throughout the field and let the tool calculate plants/acre for you.
    • Check poor areas as well as good areas and investigate reasons for poor emergence or gaps in the seed row.
  • The plant stand assessor is specific to soybeans, but the calculator itself can be useful for all other crops.
  • Compare your achieved plant stands with the table above for other pulse crops.

 

Cutworms in Soybeans and Pulse Crops

Lupin seedling with cutworm feeding damage on one cotyledon.

Scout areas of the field that have missing plants or wilted, notched or gouged plant parts. Look for signs of cutworm feeding, which often appears as chomps taken out of the cotyledon or stem or clipped stems. Dig around damaged plants to find cutworms. They move deeper in the soil during the heat of the day and it may be easier to spot them under cool conditions or in the evening when they feed. With cool, moist soils it should be easy to find them near the soil surface.

Peas and faba beans are more resilient to cutworm feeding than soybeans and dry beans. Peas and fabas may easily regrow or branch from below-ground nodes if stems are clipped while growing points of beans are aboveground and easier to damage.

Nominal thresholds:

  • Soybeans and dry beans: 1 or more cutworms (<2 cm in length) per metre of row, or 20% of plants cut
  • Peas and faba beans: 2-3 cutworms (<2 cm long) per square metre

The size of the cutworms found will be an indication of damage to come. Small cutworms have more feeding ahead of them than larger cutworms. Once they have reached lengths of 30-35 mm (1.2-1.4″), most of their feeding has already occurred.

Foliar insecticides are available for cutworm control and patch control is often the most economical decision. Best results occur if applications are made in the evening.

Ground beetles and parasitoid wasps are two beneficial insects that will reduce cutworm numbers. In years with wet soil conditions, fungal pathogens can also reduce cutworm populations.

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