View from the Field – East

By: Terry Buss, MPSG Production Agronomist – East

Pulse and Soybean Crop Update for Eastern Manitoba for Aug. 19, 2026

Field Peas:

• Crop stage ranges from from late R6 (mid maturity) through R7 (full maturity and drying down) to harvest ready with harvest ongoing. Pre-harvest herbicide applications continue and it was noted that the crop moved to maturity rapidly over the last two weeks.
• If the weather is favourable, crop dry down and harvest are expected to be rapid. At this time, too few fields have been harvested to determine average yields.
• While mould/sclerotinia has been noted on some of the more leggy crop and particularly in crop that lodged which created canopy conditions more conducive to disease development.

Soybeans:

• In the majority of fields, crop stages range from mid to late R5 (seeds are 1/8 inch long in the pods at one of the four uppermost nodes of the mainstem) to early R6 (pods contain green seed that fill the pods to capacity at one of the four uppermost nodes of the mainstem).
• Septoria brown spot remains the most commonly observed disease across fields with limited presence in the lower and sometimes mid canopy and not an economic concern. White mould is becoming more apparent in particularly leggy fields and especially those that are demonstrating some lodging. Wilted plants peaking out over the canopy is the most common symptom but severity of the disease observed thus far is well below the 10 per cent of plant population threshold. Overall presence and severity of while mould has been lower than last year.
• Soybean aphid populations have been increasing in fields but the arrival of the aphid population in Southern Manitoba has been on the late side, limiting the time the pest has to increase populations to economic levels and cause yield loss.
• A limited number of field across Eastern Manitoba have had insecticide applications to control aphids. There has been no pattern to affected fields. Producers are encouraged to monitor all their fields carefully as populations of soybean aphids can ramp up quickly.
• As the crop closes in on growth stage R6, soybean aphids have less and less time to cause yield loss. Many producers are now taking into account the pace of crop development as part of their evaluation of fields. Most crops are expected to reach R6 and not require any control measures for soybean aphid this year. Careful scouting will determine if this prediction holds.

Field Observations up to Aug. 19, 2026

Timely Rainfall Comes to Parts of Eastern Manitoba

• A relatively wide ranging rainfall event covering a large portion of Eastern Manitoba began on Friday, Aug. 14 with highest accumulations occurring Saturday, Aug. 15. Eastern and Interlake areas saw the highest rainfall amounts in general.
• Rainfall accumulations varied widely from just a mm’s to over 70 mm’s with many areas receiving at least 15 to 20 mm’s.
• Clusters of pods at the top of soybean plants in August hold the opportunity for average/good yields to move to good/ great yields. Timely rainfall in August tells the tale. For those areas receiving, 25 mm or more, the possibility of a late boost to yield now exists.

Diseases Severity Remains Moderate Thus Far…

• Most common disease being observed on soybean in 2026 is Septoria Brown Spot at the bottom of plant canopies which is in line with what we see every year. This disease has never been observed at concerning levels in Manitoba production.
• As well, natural leaf yellowing and senescence is starting to be observed in earlier maturing crop along with advanced symptoms of Septoria Leaf Spot.
• Wilting plants sticking out above plant canopies are most often infected with white mould on the lower to mid stem and are being more readily observed. So far these plants are being found in leggy plant stands, lodged plants stands and parts of fields with very high plant populations, like double seeded areas.
• White mould infection rates of one per cent or less have been observed thus far which is well below the 10 per cent threshold which is considered the point to start being concerned. Varietal differences in white mould tolerance appear to be evident again this year. White mould levels in stand thus far are below what was seen in some areas of eastern Manitoba in 2025.

Soybean Aphids – Under Scrutiny Until R6

• With the crop in R5, the window is starting to close on our concerns around soybean aphid. However, growers are encouraged to continue to monitor fields closely.
• Soybean aphid numbers per plant aren’t the only consideration in making a decision around an insecticide intervention. Now the time the plant has left until reaching the R6 growth stage, comes into play.
• Remember that the R5 growth stage can last from about 11 to 20 days with the average duration about 15 days.
• Also consider the concept of aphid days – The amount of yield loss caused by one aphid feeding on a plant for one day. As an example, 500 aphids feeding on a plant for 20 days can lower yield by about 6.88 per cent. Use this as a guideline when you consider both aphid numbers being observed per plant and the days of plant growth left until we cross the line into the R6 growth stage.
• Also observe the natural predators at work. I have observed ample lady bug larvae and hoverflies in fields where soybean aphids are present. They’re our allies in this battle and should be given the opportunity to do their work.
• Overall, my prediction is that most fields will achieve the R6 growth stage before soybean aphids cause economic yield loss. However there have been isolated outbreaks of high soybean aphids number on some longer season, later maturing fields that will require control over the coming days.
• When scouting for soybean aphids, remember to pull plants out and look at them from bottom to top paying close attention to the undersides of leaves, plant stems and pods. It doesn’t matter where on the plant the aphids occur – they can feed on any above ground plant part. An accurate estimate of aphid numbers and sampling over multiple days to determine whether populations are rising or falling is key.

Cumulative Plant Stresses Taking their Toll on Some Fields

• There have been some fields experiencing multiple stresses over the last two weeks that are likely to result in economic yield loss.
• Two symptoms being seen together are soybean aphid infestations above economic threshold paired with potassium deficiency.
• Both of these problems are heavily influenced by a lack of soil moisture, i.e. drought conditions. Soybean plants under moisture stress are more attractive to soybean aphids. The aphids migrate across fields faster and reproduce more quickly in these situations.
• Potassium moves into the plant by mass flow of soil water. Even soils with adequate potassium soil test levels may produce potassium deficient plants if the plant cannot take up adequate soil moisture. This “drought-induced” potassium deficiency is most often seen from late July to late August on drier years.
• When investigating potential potassium deficiency in soybeans, make sure to take soil tests as well as plant tissue tests to accurately determine if a soil deficiency actually exists or if the situation is “drought-induced”. Tissue testing alone isn’t sufficient to make an accurate diagnosis.