Crop Advisor’s Casebook: Thin plant stand in this wheat field

A Crop Advisor's Solution from the June 6, 2017 issue of Grainews

Because the wheat crop had a thin stand, there was high weed pressure. 
Plant density was 180 to 190 plants per square metre. Ungerminated seed seemed to be the heart of the problem.
Dan Friesen. photo: Supplied

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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