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Manitoba’s soybeans progressing well

Dennis Lange says by early September most fields will be mature enough to avoid yield loss from frost, although quality could be reduced

Manitoba’s soybean crop is looking good, Dennis Lange, Manitoba Agriculture’s industry development specialist for pulses, said Aug. 17, during the CropTalk Westman webinar.

“From what I am seeing right now we will probably be somewhere around that 35- to 38-bushels-per-acre average,” Lange said. “They are looking pretty good. We’ve had good rains. The rains we’ve had lately, right after critical time for pod filling, there is potential for some very good yields this year.”

Last year Manitoba soybeans averaged 38 bushels an acre just slightly below the 2013 record of 39.

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The five-year average yield is 35 bushels an acre.

Most areas of Manitoba have been warmer than normal, which helps soybeans, he said.

However, several diseases have been found in soybean fields. One is white mould, which is the same fungal disease sclerotinia that attacks canola. But it’s late enough in the season big yield losses are unlikely, Lange said.

White mould symptoms include white mycelium in the lower part of soybean plants.

“If you have 10 per cent infection in the field it can cost up to three to five bushels (an acre),” he said. “But when you think about it 10 per cent is a lot. In an acre if you have 140,000 plants that would be about 14,000 plants that would be infected.

“Right now in the (Red River) valley we haven’t seen a lot of white mould yet. We have seen the odd field. Typically where we are going to see it is in areas of really dense canopies.”

Given all the rain and high humidity and thick crops some white mould infection is expected, Lange said.

“We have a saying in the dry bean business — ‘no mould, no gold,’” he said. “If you don’t have a little bit of a dense canopy you don’t have big yields either. Keep that in mind when you are out scouting as well.”

Farmers with white mould this year might want to consider a slightly reduced soybean plant population next year. Fungicides applied at the R1 to R2 stage will also help protect soybeans from infection.

Some soybean fields are infected with septoria brown spot in the lower to mid-canopy, Lange said.

“It’s not something that causes any economic damage, but when you are out there it gives you an idea of what level of disease you do have,” Lange said. “It may be something to watch for in the future.”

Phytophthora root rot is also present in places. Look for a black discolouration at the base of soybean stems. Leaves on infected plants will wilt and hang on to the plant, Lange said.

Bacterial blight can infect soybeans. It’s usually in the mid- to upper canopy of soybean crops. This disease, which can’t be controlled with fungicides, usually follows crop damage caused by heavy wind or rain.

Bacterial blight can be spread by travelling in infected fields when wet. Infected crops usually improve with the emergence of new growth.

As of Aug. 17 most Manitoba soybean fields were in the R4 to R6 stage, Lange said.

Crops at R6 stage have about 18 days to reach R7, Lange said. It takes another nine days from R7 to R8.

“Harvest is fast approaching,” he added. “Once we roll in September I think most of the (soy)beans will be safe from frost this year.”

Frost at the R5 stage can cut soybean yields 50 to 70 per cent, Lange said. At R6 frost can reduce yields 20 to 30 per cent.

Although there are many good soybean varieties available to Manitoba farmers, it’s important farmers select ones that fit the growing conditions, Lange said.

“Most farmers are selecting varieties suited to their areas but one of these years there will be an early frost and (crop) damage,” he warned.

Soybean growth stages

  • R1 — When the first flower is anywhere on the main stem.
  • R2 — Flowers on the top two nodes.
  • R3 — First pods starting to show on the first top four nodes.
  • R4 — Pods are three-quarters of an inch long in the uppermost nodes of the plant counting down from the top.
  • R5 — Flat pods on the top four nodes.
    Between R5 and R6 is when the plant reaches its maximum height and maximum number of nodes. The seeds at R5 are about an eighth of an inch long and fairly flat with a little bit of a bump in it. Hail damage at this stage can dramatically reduce yield.
  • R6 — Full seed counting in the top four nodes. When the pod is split in half seed fills the entire pod cavity.
  • R7 — One normal pod has matured and turned brown and the leaves are starting to drop. Yield loss due to frost at this stage is minimal, but quality can be reduced.
  • R8 — Full maturity is 95 per cent brown pod and the pods rattle when shaken and there are no leaves left. Crops at this stage are 10 to 14 days away from harvest.

Seed Manitoba maturity ratings are based on days from seeding to 95 per cent brown pod.

About the author


Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.



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