[UPDATED: Sept. 23, 2020] Widespread frost in western Manitoba last week damaged longer-season crops, but the extent wasn’t known at press time, and in many cases won’t be until harvest is completed.
Some farmers on social media said they feared their soybeans were severely injured. But it might not be as bad as some think unless the soybeans were still in the R5 stage, Dennis Lange, Manitoba Agriculture and Resource Development’s (MARD) pulse crop specialist, said in an interview Sept. 10.
The same can’t be said for corn, which was generally much further away from full maturity, Manitoba Crop Alliance extension agronomist Morgan Cott said in an interview Sept. 9. However, she’s more optimistic about sunflowers.
Meanwhile, MARD officials reported during the department’s Crop Talk webinar as of Sept. 8 that Manitoba farmers were harvesting above-average cereal and pea yields, but “disappointing” average to below-average canola yields.
Soybeans were looking better than last year and Lange still expects the 2020 provincial average yield to exceed 2019’s, below-average 28 bushels an acre.
Why it matters: Despite a slow start this spring followed by myriad weather and insect stresses, Manitoba’s crop was generally looking good, and still is, despite last week’s frost. But it’s also not all in the bin yet.
How badly a crop is damaged by an earlier-than-usual fall frost depends on the crop’s maturity, how cold it was, and for how long.
Freezing temperatures ranging from -1 to -5 C were recorded across western Manitoba overnight starting Sept. 7 into the morning of Sept. 8 (see map below).
Pretty much everywhere west of a line running from Miami in the south to Ethelbert in the north saw frost that lasted from four to 10 hours.
Temperatures generally got colder from east to west.
Pockets of the Red River Valley received frost the morning of Sept. 9.
Jennifer Seward said in an interview her family farm’s silage corn, near Graysville, shows signs of frost damage.
Lange said a farmer near Altona also saw signs of frost in his dry beans.
“For the most part I think the (soy)beans should be OK,” Lange said during the Crop Talk webinar, adding that most soybeans in the west were in the R6 (reproductive) stage. “It will hasten maturity and because there is enough green leaf material there you shouldn’t see too much of an issue with loss of yield. You might see a few green kernels.”
In an interview later Lange said soybeans frozen in the R5 stage could see yield losses of 50 to 70 per cent.
The R5 stage starts when a seed is one-eighth of an inch long in a pod at one of the four uppermost nodes and ends when those seeds are fully formed (R6).
Lange said he doesn’t know how many soybean fields were R5 when frozen. Normally this time of year 80 per cent would be R6 to R7, he said.
In the R6 stage soybean fields are still green but seeds fill the pod. At this stage frost can cut yields 20 to 30 per cent and result in some seeds staying green.
“If it’s light frost you might just see the top pods go so it would be at the lower end (of yield loss),” Lange said.
In R7 soybean fields the majority of pods are yellow and at least one pod on the main stem is brown. The crop is physiologically mature. A hard frost then might cut yields by five per cent.
At R8 the field is tan brown and 95 per cent of pods are brown. Seeds will rattle in the pods and all leaves will have dropped. Frost at this stage doesn’t affect yield or quality.
Seeds in green pods at the top of frozen soybean fields will likely be lost or go out the back of the combine at harvest, Lange said.
Some green-seeded soybeans will turn colour before harvest, but farmers shouldn’t delay harvesting fields waiting for seed colour change, he said.
Some binned green seeds will also turn colour in storage, Lange said.
Most soybeans are sold as Canada No. 2, which allows up to three per cent green seed, he said.
*Oak River seed grower Eric McLean, is worried about his 1,500 acres of soybeans. They are grown for seed and have varying maturities.
“We probably got 600 to 800 acres that are affected drastically (by frost) and the balance is affected to various degrees,” McLean said in an interview Sept. 10.
“In our neck of the woods we had 10 hours of below-freezing temperatures and we do believe some of our canopy was penetrated right to the bottom. Dennis (Lange) is correct we’re going to have extensive leaf drop and accelerated maturity now. The big question now is how much filling will happen and how much green seed will be locked in and what is going to be salvageable.”
McLean said he expects his earlier-maturing soybeans to fare the best because they were the most mature. *He sowed his earliest-maturing soybeans first and latest maturing last to stagger harvest.
“We have some soybeans that were as green as your lawn,” McLean said. “I don’t know if they are going to make it or not.
“We’ve just never seen it where a whole field will be affected and that’s what we’re facing now.”
While McLean finished planting soybeans May 25, he knows some farmers had to seed later because they had last year’s crop to remove first.
Cool weather delayed all crop development this spring as well. So did six inches of rain at the end of June and into early July.
Ample moisture also kept soybeans growing longer this year, adding to farmers’ hope for an above-average yield, McLean said.
Most Manitoba grain corn crops needed another three or so weeks before they would be safe from frost, Cott estimated last week.
Unfortunately, it was cold enough in much of western Manitoba to damage both grain and silage corn crops, she said.
“We are still at a stage where we could see big losses if we get a severe frost and we could see serious quality being lost also, just like we did last year, because the grain won’t fill… and we have light test weights and the possibility of mould because grain is not drying,” Cott said.
Grain corn is not mature until the yellow colour in the seed reaches the cob, which is referred to as the black line or black layer.
This time of year most sunflowers are fairly frost tolerant, but prolonged temperatures of -4 C or colder can cause damage, Cott said.
“I’d keep an eye on it, but generally it shouldn’t be a huge concern,” she said.
Often grain corn that freezes before maturing is cut for silage to feed cattle.
Before ensiling frozen corn, farmers should be sure it’s still not too wet, MARD livestock specialist Tim Clarke said during Crop Talk.
“I wouldn’t get into too much of a hurry to chop right now unless that corn crop has been drought stressed for quite awhile and then it might be under 67 per cent moisture standing,” he said.
The ideal moisture level to ensile corn is 67 per cent. Ensiling corn can be done when the milk line has progressed one-eighth to seven-eighths down the kernel. The ideal milk line is 50 per cent with moisture under 70 per cent, he said.
While frost will kill and dry up corn leaves, most of the moisture comes from the cornstalks and cobs, Clarke said.
The Manitoba Agricultural Service Corporation (MASC) got a few farmer calls about crop insurance following the frost, David Van Deynze, vice-president innovation and product support, said in an interview Sept. 9.
Unless the damage is so bad the farmer wants to rip the crop up, MASC’s advice is: “Combine it and give us a call when you’re done.”
(Farmers are obliged to contact MASC before destroying any insured crop.)
“There will be some yield hit there for sure, but it’s likely more of a quality concern, which impacts their insurance as well,” Van Deynze said. “They are covered for quality too.”
Earlier this year MASC estimated Manitoba farmers seeded 1.1 million acres of insured soybeans, 313,194 acres of insured grain corn, 129,886 acres of insured silage corn, 67,614 acres of insured oil sunflowers and 25,325 acres of insured non-oil sunflowers.
*(UPDATE: The location of Oak Lake was changed to Oak River, and Eric McLean’s soybean seeding plan was updated.)