By: Wendy McDonald, MPSG Production Agronomist – West
Pulse and Soybean Crop Update for Western Manitoba field conditions up to Aug. 28, 2026
Thursday, Aug. 20
I really enjoy scouting fields when farmers and agronomists come along with me. We all learned so much when we were at this soybean field near Russell.
Guess what the storms blew in? Soybean aphids. Long distance migration is mind boggling but aphids arrive in Manitoba from the United States by hitching a ride on the jet stream. I received many calls from the Parkland and western Manitoba regions about soybean aphid numbers, scouting, crop stage, and possible control options.
Most soybeans were still in R5 stage (above), and could still be affected by aphid sucking and feeding on plant sap in the phloem of all above ground plant parts until plants reach R6. R6 is called full seed and is when the green soybeans inside the pod are as big as they are going to get, at least one pod on the top four nodes of the main stem.
Estimating Yield Loss
A unit of measure that can be used to estimate yield loss from aphid feeding is called cumulative aphid-days. One aphid-day equals one aphid feeding for one day. Ten aphid-days could be 10 aphids feeding for one day or one aphid feeding for 10 days. According to research, soybean yield is reduced by 6.88 per cent for every 10,000 aphid-days accumulated. Therefore, 500 soybean aphids per plant on average feeding for 20 days would incur approximately seven per cent yield loss.
Amount of yield damage from aphids depends on the number of aphid days we’ll experience until plants reach R6. Aphids prefer the juicier newest soybean growth and that’s why we usually find them in later seeded soybeans.
When aphids have been feeding on plants for awhile, you will see a lot of cast skins and excreted “honey dew” on all above ground plant parts. It can be hard to tell what are actual aphids and what are cast skins when looking quickly.
I did read that if aphids look bloated or fuzzy, they could be infected with a fungus that can kill most of them.
The honey dew is shiny, sticky, and sugary and later sooty mould growth can thrive in the honey dew areas. Heavy duty aphid populations can cause flowers and small pods to not form properly. It’s the combination of plant nutrients removed by the aphids and mould covered leaves that can cause yield reduction.
If we find beneficial insects in the field they can control aphid populations quite nicely. That’s an excellent sign to re-evaluate aphid populations before making a spraying decision. Each lady beetle larvae can eat over 100 aphids a day!
We were amazed to watch this ver hungry flower fly larvae in action, searching out and sucking up soybean aphids. Larvae are legless and can be green or brown. The contents of their body are visible through their skin!
We saw these flower fly adults and that gave us another hint as to what type of larvae was in the video. Flower flies are also called hover or syrphid flies. Adult flower flies don’t eat aphids.
We also saw only one or two soybean loopers. They also blow in on the jet stream. They only eat leaves and not usually pods, so they don’t typically cause economic damage.
We also came across a brown stink bug that can feed on stems, pods, and seeds.
We found one plant with white mould symptoms.
This pea field near Menzie still had green areas and was not quite ready for desiccation.
Then it was time to survey fields for the Manitoba Agriculture faba bean disease survey. These faba beans near Menzie were taller than my shoulder!
A few lush and tall areas had some lodging, but look at all those pods.
Even though this field was sprayed twice with fungicide, like almost all faba bean fields, the leaves have brown lesions. The lesions could be caused by stemphylium blight or chocolate spot (botrytis) or alternaria.
It gets even more difficult to tell what exactly is on the leaves as the lesions expand.
Several branches have shrivelled back and no pods have formed at the lower parts of this plant.
This entire plant has prematurely blackened and has wilted the stem and leaves.
Stem infection part way up the plant, raised orange dots.
This could be chocolate spot, rust coloured lesions on the faba bean seed.
The best part is visiting with farmers in their field, and they got all dressed up for crop checking.
These faba beans near Elphinstone look fantastic and the sunset is pretty amazing too.
For the faba bean disease survey, we send 10 leaves from five sites in each field to Agriculture and Agri-Food Lethbridge for examination and diagnosis.
Immature faba beans are filling the seed pod cavity. They’re still attached to the pod wall. The white on the pod wall is normal as the pod is thick and fleshy.
Faba beans produce a tremendous amount of flowers but not every flower results in a pod. This is pretty good seed set here.
We did find some plants with blackened, shrivelled, sporulated pods with no seeds inside of them.
For the disease survey we pull up five plants at five different sites in the field. This field and beautiful sunset is near Newdale.
We send the roots to Agriculture and Agri-Food Morden where they take slivers of root tissue and plate it out to further examine for root rot disease identification. These lower stems also seem to have some symptoms.
Just me and the mosquitos wandering through the faba beans.
Friday, Aug. 21
Dry beans that have been undercut south of Carman.
I wonder what type of beans are inside this greenish pod?
It’s still tricky to tell when the seed is immature.
Look at that…must be kidney beans.
This field of soybeans near Portage la Prairie had random patches of soybeans with wilting leaves. Only certain branches had senescing, and there were lesions on the stem that started and ended part way up the plant. But it still had decent roots and nodules.
This could be phyllosticta leaf spot. It can spread to stems and pods too. These lesions are not just interveinal.
These pods had colour striping and were starting to shrivel. The stem was dying, and leaves were curling.
Linear row of black specks on the stem, this could be phomopsis stem blight.
Monday, Aug. 24
A lot of pea harvest progress was made over the weekend in the Parkland, with reports of yields between 30 to 70 bushels per acre. These peas near Grandview are ready to go.
Vertical tillage being done on pea stubble.
This bear was wondering where all the peas have gone.
Tuesday, Aug. 25
The afternoon had scattered showers but I was able to survey this faba bean field near Riding Mountain. These speckled leaves top to bottom, could be early symptoms of chocolate spot.
Wednesday, Aug. 26
I was so happy to be able to spend a great day with Manitoba Agriculture provincial pathologist Shuanglong Huang. He also goes by Simon. We toured fields and took samples near Gilbert Plains and Grandview and I asked him a lot of questions!
Simon was interested in finding sclerotia bodies for a tolerance study. He was looking for fields that were soybeans seeded on canola stubble to see if there was higher incidence of white mould. We didn’t see much for white mould today, maybe symptoms will show up in a few more weeks.
This soybean field near Gilbert Plains was loaded with aphid eating lady beetles. When we were in this field, we were startled when we heard gun shots, but then remembered we weren’t that far away from the Gilbert Plains shooting range!
I had gotten some questions about the how dissimilar the different stages of the lady beetles can look. Here above we see lady beetle larvae and lady beetle pupae.
These “mini alligator looking guys” are lady beetle larvae and each one eats over 100 aphids per day.
Here we see a few aphids and some brown stink bugs.
This looks like cercospora leaf blight as it’s occurring in the upper most canopy—this may lead to purpling stems.
This looks like fusarium root rot.
This plant doesn’t have lesions that start at the soil line, they’re higher up the plant and leaves are wilting.
The distinct rows of black specks on this stem lesion suggest it could be phomopsis.
Here is a closer look at the pycnidia in distinct rows and prematurely killed petioles and stems.
This could be frog eye leaf spot.
Middle leaf is cercospora and lower leaf is septoria brown spot.
We snipped stems up the middle to check for any internal browning but this stem was white.
South of Grandview a farmer passed us on his way to seed some winter wheat.
Near Grandview, this plant had wilting leaves and stem discolouration from the soil level upward, but very healthy roots, so not Phytophthora root rot.
Watch and listen as Simon explains the symptoms.
Blocky, not circular lesions on this leaf.
Not so sure because cercospora is typically only on the upper leaf surface and this is on the underside of the leaf only… but this leaf spent most of its time flipped up.
It’s important to check prematurely yellowing patches of the field.
They could be phytopthora root rot or sign of patches of soybean cyst nematodes. In this case it’s low laying area that would have held a lot of water and I suspect is very high in salts, as it’s a reclaimed pothole area.
The upper leaves could be potassium deficiency and the lower leaves could be same but leaves edges have already gotten crispy.
We found some stem lesions in these faba beans too.
This faba bean pod has split and is showing signs of disease, maybe ascochyta blight.
Thursday, Aug. 27
Faba beans near Erickson, there were some great looking pods.
This plant was infected part way up and all branches and the upper stem were affected.
Alfalfa and faba bean intercrop, no applied nitrogen needed and sure helps with weed control.
Soybeans near Fork River that looked lush and green.
Plants with beautiful leaves that had lots of healthy pods.
There were huge nodules on these roots.
This nodule was green inside when squeezed, so even though it looks really good from the outside, it wasn’t functioning.
This area with yellowing leaves is…
…maturing normally and the pods have turned yellow.
The seed inside still had a touch of greenish tinge to it.
Friday, Aug. 28
The peas at our regional variety trials near Souris have already been harvested.
The faba beans at the MPSG regional variety trials near Souris are turning darker as they naturally mature.
It’s interesting to see the maturity differences of the dry beans varieties which were seeded in narrow rows at the MPSG regional variety trials near Souris.