JULY 31, 2024

• Crop Update
  • Growth staging guides →
  • Scouting calendars →
  • Staging Peas for Desiccation Timing →
• Symptoms We’re Seeing in the Field
• Phytophthora Root and Stem Rot in Soybeans
• Northern Stem Canker in Soybeans
• Soybean Cyst Nematode
• Watch for Waterhemp
• Lygus Bugs in Faba Beans

Crop Update 

Soybeans range from R3 (beginning pod) to R4 (full pod).

• Soybeans have been responding well to the heat with biomass increasing significantly in most fields. With this quick growth increase we are seeing signs of some rapid growth syndrome. This shows up as bubbling and crinkling of the new leaves since the leaf interior is growing quicker than the veins and leaf edges can keep up.
• Moisture limitations are apparent in some fields, where soybeans have flipped their leaves over to reflect sunlight to conserve moisture.
• Soybean aphids have been confirmed in a few fields at low levels. Natural enemies have been able to manage aphid levels so far. View product options for control here if thresholds reach above 250 aphids per plant and increasing.

Field peas range from R4 (full pod) to R5 (beginning maturity), with some earlier seeded fields being close to R6 (mid maturity).

• Pea aphids are being found within pea fields, however the most susceptible staging to pea aphids is at pod formation and elongation. Most fields are past R4, and at this staging pea aphid feeding is not expected to impact pea yield.
• Once peas have reached the full pod stages where seeds have filled the pod, fungicide applications are no longer recommended as we’re within the 30-day pre-harvest interval of several products, and because disease is no longer expected to affect yield.
• Starting to think about pea harvest and desiccation? See Staging Peas for Desiccation Timing →

Dry beans range from R2 to R5, at the pin bean stage to pods that are 3 to 4 inches long with seeds developing.

• Fungicide applications for white mould are on-going. For second fungicide application decisions, visit Fungicide Decisions in Dry Beans →
  • Fungicide Options in Dry Beans →
• Potato leafhoppers have been observed causing some damage on a few plants in the headlands on some fields. Small, triangular brown areas at the tips of leaves is a sign of ‘hopper burn’. Economic thresholds are 2 leafhoppers/trifoliate at R1 and numbers observed in the field have been well below this threshold.
• The bacterial blight complex has set in at most fields, with brown lesions with yellow halos on leaves. Common bacterial blight, bacterial brown spot and halo blight all operate within this complex. Learn more at the Dry Bean Tour on August 7 in Morden!

Faba beans are at R5 (full pod) with pods developing on the upper nodes and full seeds at the lower nodes.

• Foliar symptoms of several diseases look very similar in faba beans. This year, the first faba bean disease survey has kicked off to better identify diseases of faba beans. Infected leaves and roots are being collected for diagnostic testing to improve our understanding of diseases in faba beans.
• Pea leaf weevil larvae and pupae are easy to spot when digging up faba bean roots this time of year. More information on pea leaf weevils →
• 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). Faba beans are most sensitive to aphid feeding while flowering. Natural enemies of aphids include lady beetles (adults and larvae), hoverfly larvae, lacewing larvae, parasitism and more. Faba bean yields are improved by pollinators in the field, so if control is warranted, use practices that minimize effects to pollinator species. When considering product options, be aware that pyrethroid resistance has been suspected in Saskatchewan.
• 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) →

Listen to the Bean Report:

Symptoms We’re Seeing in the Field

There are a lot of great crops out there but also challenges in different areas of some fields. Below are photos of various diseases and environmental symptoms we have been seeing in the field. Read the photo captions for more information!

Phytophthora Root and Stem Rot in Soybeans

Phytophthora root and stem rot (PRR) is a root and stem disease specific to soybeans that can infect at any growth stage. Part of PRR’s life cycle depends on soil moisture for the disease to swim to infect plant roots. With more soil moisture this growing season, we expect to find more PRR symptoms in the field this season.

• Symptoms appear as brown lesions that extend upwards from the soil line, and roots are discolored and unhealthy. Plants will be wilted and leaves remain attached to the plant. Infection occurs in patches or as randomly-infected plants, often in headlands.
  • One look-alike to PRR is Northern Stem Canker where plants will appear wilted and there will be a brown lesion along the stem. But with stem canker, roots will appear healthy and the lesion won’t extend upwards from the soil line. Stem canker often also infects following stem damage from hail or storms.
• Genetic resistance is available to help manage PRR, and there are two types:
  • Major gene or pathotype-specific resistance: an Rps (Resistance Phytophthora sojae) gene is completely resistant to specific pathotypes of PRR in the field’s soil. Multiple pathotypes of PRR can occur in a field, so knowing which are present in the soil is crucial to use this variety resistance.
    • Last year, roughly 70 soybean fields were soil sampled for pathotype identification through the soybean disease survey. Of those fields, 83% had Phytophthora sojae present in the soil. Most commonly, pathotypes present were able to defeat Rps 1c and 1k, while Rps 3a and 6 offered the most protection versus the pathotypes present in the soil.
    • There is now a commercial soil test available to identify the pathotypes of PRR in a field’s soil from AYOS technologies.
  • Field tolerance or partial resistance: several genes resist infection within the plant and the plant is better able to tolerate the PRR infection without dying. This resistance is only expressed after the first true leaves are open, so it needs to be used in combination with an effective seed treatment.

More information on Phytophthora root and stem rot in soybeans →

Northern Stem Canker in Soybeans

Northern Stem Canker (NSC), caused by Diaporthe, can look very similar to Phytophthora root rot at this time of year. NSC was first officially documented in Manitoba in 2017, and we see it pop up in a few fields every year. It’s most common to find in fields with more soybean history or with tight soybean rotations. As a result, we often find NSC and PRR occurring in the same field. Typically, we don’t see major crop losses to NSC.

NSC symptoms usually start on the lower third of the stem after flowering. Initially, small reddish-brown lesions occur at the base of a branch or petiole and then they spread to form cankers on the stem that can spread several nodes and cause the plant to wilt like PRR. Taking a closer look at the roots gives us an indication to suspect PRR vs. NSC. Roots will be healthier with NSC infections while with PRR they will be rotted an pull easily from the ground.

NSC survives in soybean crop residues, so extending the crop rotation break can be one management option. Additionally, using tillage to increase the rate of residue breakdown can also speed up the decomposition of this disease. Some foliar fungicides will likely have activity against NSC, but it’s not often listed on the label. Varieties vary in their susceptibility to NSC, but finding information on which varieties are more susceptible than others is a challenge.

Soybean Cyst Nematode

There are no distinct above-ground symptoms unique to SCN. Since SCN impacts water and nutrient uptake, stunting, chlorosis and necrosis are common symptoms, however, once above-ground symptoms are apparent, up to 30% yield loss may have already occurred. As a result, dig up roots in August to look for cysts and to catch this destructive soil-borne soybean pest early.

Scouting for SCN:

1. Gently dig up soybean roots from late July to August and examine them for cysts. Cysts are smaller than root nodules and appear as white, lemon-shaped cysts on the roots.
   • In clay soils, roots may need to be soaked to loosen and remove soil.
   • Magnifying lenses may come in handy to take a closer look at roots in the field.
2. Target high-risk areas of the field, which includes anywhere that soil containing SCN could have been introduced. This includes field approaches and headlands, low spots and water runs, shelter belts, high pH areas and any generally low-yielding areas of the field.
3. If you suspect SCN, soil samples can be collected and submitted to Agvise to get an idea of abundance (eggs/100 cc of soil) which can guide management decisions. If samples submitted to Agvise come back positive for SCN, contact MPSG for further testing.

Management strategies include growing SCN-resistant varieties, reducing tillage and controlling host weed species (of which there are more than 110 species). Other crop hosts include dry beans, peas, clovers, and vetches, among others. Once introduced to a field, SCN cannot be eradicated, only managed.

Since SCN is just starting to get established in Manitoba, prevention is still a valuable management tool. SCN is soil-borne, so anything moving soil has the potential to move SCN. Ensure new equipment is free of soil before entering your fields. Clean soil sampling equipment and field tools between farms. It is likely that SCN is lurking undetected in several fields due to previous flooding along the Red River.

Watch out for Waterhemp!

Be on the look-out for smooth-stemmed pigweeds

Waterhemp that has been found in Manitoba has been resistant to combinations of groups 2, 5, 9 (glyphosate) and 14. With soybeans and dry beans, it is easy to spot pigweeds poking up above the crop canopy at this time of year.

Check up on those pigweeds you’re seeing in the field. If their stems are rough and hairy, it’s likely red root pigweed. If stems are smooth, it’s time for more testing. You can collect plant samples and have them tested at the PSI lab in Winnipeg or contact Manitoba Agriculture for next steps.

Waterhemp:

• Emerges throughout the growing season, typically after most other summer annual weeds have been sprayed.
• Seeds may move with water, so scout along drains, creeks and in previously flooded areas.

  

• Flourishes in row crops due to more sunshine in the inter-row spaces.
• Produces 250,000 seeds per plant, and individual plants may produce more than one million seeds.
• Is a Tier 1 Noxious Weed, meaning all of the plants must be destroyed.

Lygus Bugs in Faba Beans

Fabas are late maturing, resulting in movement of lygus bugs into fabas once alfalfa is cut or canola is swathed. Hot, dry weather promotes lygus bug development and damage can be worse under these conditions.

Yield losses are not generally a concern, but quality can quickly be impacted. Lygus pierce pods to suck plant sap. Visible damage is found on the seeds due to enzymes in their saliva. Fabas need to have less than 4% perforated damage to be graded No. 3 Canada or better.

Fabas are susceptible to lygus damage until the pods and seeds become firm and most feeding occurs at the top of the plant. Monitor fields during pod development. A nominal threshold to prevent 15% damage is five lygus bugs per 10 sweeps. At research plots in Alberta in 2015 and 2016, a single lygus bug per ten sweeps resulted in 10–12% damage.

While control may be warranted, pollinator insects are important for seed set in fabas and should be taken into consideration when making spray decisions. Having pollinators in your fabas has been shown to increase yield by 17%, on average, so use practices or products that minimize the impact to pollinators.