Lucas farms near Starbuck, Man., growing corn, soybeans, wheat, oats and canola. I received a call from Lucas at the end of June last year. He suspected he had some herbicide efficacy problems, as he noticed some redroot pigweed was not dying after he sprayed a field of corn with Roundup.

“It’s been three weeks since I sprayed, and the weeds have only got larger. They should be dead and gone,” he said.

Upon arriving, I saw exactly what he meant. There were definitely some weeds that were not affected by Lucas’ previous herbicide applications.

Herbicide resistance was top of mind for me, considering the herbicides Lucas said he had sprayed should have killed the redroot pigweed we were both looking at. There were other weeds in the field that had clear herbicide damage. They were dying off — both grassy weeds and broadleaf weeds — while the pigweed remained.

I knew we had to eliminate all obvious potential causes right off the bat. Perhaps his sprayer malfunctioned and missed the pigweed? We quickly ruled this out, as there were other patches of redroot pigweed in the field his sprayer had definitely hit — they were not in straight lines like one might expect from a sprayer miss.

Perhaps he didn’t handle the chemical properly? Nope. It turned out the chemical was well mixed and spray booms were charged before spray application began.

What about dust from the nearby road, I wondered? Road dust can often reduce herbicide efficacy. However, it wasn’t that either. Regular rainfall and calcium-based dust control had been applied before Lucas sprayed his field. Something else was at work here.

I asked Lucas about the history of this particular field that perhaps made it unique from the others. Currently, he had corn planted and he’d sprayed Roundup. In 2020, he grew soybeans and sprayed roundup. The year prior, in 2019, he grew oats and sprayed Refine SG, he said.

He had been spraying Group 2 and 9 chemistry over the past three years. Resistance could very well be the culprit, but the herbicides he had been using should have killed the redroot pigweed, which hasn’t been known to develop resistance to those herbicides. Something didn’t make sense.

It was time to do some tissue testing to see what was going on here.

Crop advisor solution: Weed misidentification, herbicide resistance lead to trouble

I took some tissue samples, and when the results came back, my suspicions were confirmed. The pigweed wasn’t pigweed at all. It was waterhemp. When I told Lucas, everything fell into place.

The field is close to large drainage ditches where water can back up onto the field during spring melt or during times of very heavy rainfall events. Waterhemp moves in bodies of water and could have travelled up the waterways and eventually deposited seeds on this field.

Waterhemp is notorious for developing Group 2 and 9 herbicide resistance, and the crop rotation Lucas used created the perfect conditions for this to happen.

Unfortunately, his yield was affected, as the weed seedbank in the field bolstered.

Lucas has committed to changing up his crop and herbicide rotation and to use tools that are effective in controlling waterhemp. Other possible herbicides that could be used, depending on the crop, to reduce waterhemp in the field include pyroxysulfone, dicamba and sulfentrazone.

Thankfully, using these other modes of action, Lucas found he had better weed control and was able to continue growing crops that diversified his rotation.

I encouraged him to properly identify weeds as early as possible in the future and control them in a timely manner using different chemical modes of action. This would be a recipe for success and should prevent further issues with waterhemp.

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John, a Manitoba producer, asked me for a recommendation on an in-crop herbicide that would best suit the needs of his wheat crop.

It was the end of May when I made my way out to John’s 3,000-acre farm near Starbuck, Man. I wanted to scout his field before advising him on crop inputs.

When I approached the field, I thought the wheat crop looked normal. However, the initial scout revealed the crop had a thin plant stand. After carrying out plant stand counts, I confirmed wheat plant density in this field was lower than average, with approximately 180 to 190 plants per square metre. As a result, higher weed pressure was being exerted on the crop.

At this point, I thought it was important to determine the cause of the thin plant stand. Examination of insect pressure and environmental stresses were good places to begin. John thought we should also look at seeding depth and fertilizer placement.

“Maybe I seeded too deep,” he told me, “or applied too much phosphate fertilizer in the seed row.”

That season, weather conditions had been favourable for crop growth. Thus, neither precipitation nor excess heat were factors decreasing plant stand density, and adverse environmental conditions could be stroked off our list.

In addition, we didn’t find any insects, or evidence of pest damage, that could be responsible for the thin plant population.

John and I dug in the soil looking for seed to determine the seeding depth of the crop. We found ungerminated seed at the correct depth, eliminating another possible source of decreased plant density.

Also, soil moisture levels were good, and John’s seed drill has a two-inch spoon opener, ensuring the safe application of 77 pounds per acre of 11-52-0 (monoammonium phosphate) fertilizer, while also preventing salt toxicity. His drill also has mid-row banders for placement of 46-0-0 nitrogen (urea), eliminating the risk of seed burn due to additional salt or ammonia toxicity.

After ruling out these other factors, I knew we had to re-examine the cause of the ungerminated seed we had found earlier that day. I felt the ungerminated seed was at the heart of John’s thin plant stand mystery.

Crop Advisor’s Solution: Review germination reports before seeding

After eliminating insect pressure, environmental stresses, seeding depth and fertilizer placement as sources of the thin plant stand, we scrutinized John’s routine seed and soil tests.

John admitted he didn’t read the results of the one test that could have made a difference to his plant stand — the seed germination test.

According to laboratory test results, the bin-run seed’s germination rate was 78 per cent, which resulted in the wheat field’s low plant stand density. Consequently, the crop was experiencing more weed pressure and more tillering.

With more tillers, in addition to an in-crop herbicide, the fungicide timing at heading was closely monitored for a two-pass application strategy because the crop was at varying stages of flowering.

However, at harvest, yield was reduced, and increased fusarium was present in the grain sample.

In addition to germination rate, having seed analyzed provides useful information, such as seed vigour and presence of disease, which can then be used to determine optimal seeding rates. Seed analysts can also offer ways to improve germination of a seed lot with the information provided by test results.

In this case, the purchase of treated, certified seed would have produced a wheat field with a high germination rate and minimal disease in, or on, the seed. This year, John will start the season

off with treated, certified seed to reduce disease risk, and he will be able to set his seeding rate based on seed size and optimal plant stand density.

Dan Friesen works for Richardson Pioneer Ltd. at Starbuck, Man.

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In mid-May I got a call from David, who grows 2,000 acres of canola, wheat, soybeans and peas on his farm in southeastern Manitoba. It had been three weeks since David had planted his canola crop, but he was seeing very poor emergence in the field.

David had hoped for eight to 10 plants per square foot, but so far only two to four seedlings per square foot had appeared in the seed rows. With so few canola plants emerging, he suspected seed might be the issue.

“I think I received a bad seed lot, and that has caused poor germination,” David said.

He asked me to come out and have a look at his canola field. When I arrived at David’s farm, I was told the weather had been fairly dry in recent months, and that soils in these fields were a mixture of clay-loam and sandy-loam.

I performed a plant stand count right away and confirmed that relatively few seedlings had emerged. These findings were uniform across the entire field, and there were no signs of patchiness indicating some areas were affected worse than others.

Prior to visiting David’s farm, I had called the seed supplier to enquire about the canola seed lot. The supplier reported that no one else had experienced germination issues with this seed batch, ruling this out as a source of the problem. But if bad seed wasn’t to blame, what was?

I wasn’t sure, but I suspected the issue might have something to do with chemicals applied to the field. When I looked at the grower’s application records, I could see that no residual herbicide had been used the previous year, and that a glyphosate product had been applied that spring just prior to planting.

With respect to nutrients, David had applied a primary source of nitrogen as anhydrous at a rate of 100 pounds per acre the previous fall. A 36-50-0-20 fertilizer blend had also been applied at planting, in an effort to boost phosphorus levels in the field. I also learned that the fertilizer had been seed-placed with a narrow opener disc drill.

Crop Advisor’s Solution: Too much phosphorus

Looking at David’s nutrient blend sheet for the field, it was evident that he had exceeded the recommended rates of phosphorus and sulphur in the seed row. This had produced a high level of salt toxicity as well as some ammonium toxicity in the soil — both of which would have caused plant damage to occur and led to fewer canola seedlings surviving to make it above ground.

Unfortunately, there wasn’t much the grower could do to rectify the situation, and he ended up with a reduced yield for his canola crop that year. I urged David to be more careful with how he applied nutrients in the future and that he also consider using other rotational crops that are more tolerant of fertilizer as a better solution to increasing phosphorus levels in the field.

In addition, I recommended a number of changes in his nutrient program for the following planting season. These included putting less phosphorus down with the canola seed and using any leftover product with other crops better suited to handling higher quantities of seed-placed phosphorus. I suggested he try different sources of phosphorus fertilizer that aren’t as potentially toxic to canola plants, and I urged him to not to hesitate to ask for a second opinion when it came to crop nutrient plans.

David took my advice, and the following year he had a much better canola crop. The plant stand this time around was right on target, at eight to 10 plants per square foot.

Dan Friesen is a sales agronomist with Richardson Pioneer Ltd. at Starbuck, Man.

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