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Crop advisor casebook: Durum wheat mystery revealed

A Crop Advisor's Solution from the December 1, 2020 issue of Grainews

The durum stand was thin and uneven, with numerous bare rows as well as areas that had lots of sickly-looking plants. Where germinated plants had emerged, many of them were turning yellow and were starting to wilt, particularly the larger three-leaf plants.
Austen Preete. photo: Supplied

David runs a grain operation about 30 kilometres southwest of Moose Jaw, Sask., growing durum wheat, canola and lentils on his 4,500-acre farm. In the third week of June, I got a call from the producer saying his durum crop was doing poorly.

David told me the durum stand was thin and uneven, with numerous bare rows as well as areas that had lots of sickly-looking plants. Because his farm had just received its first significant rainfall of the year, David had been hopeful this weather event could turn things around in the field, but that hadn’t happened.

“I thought all this crop needed was some rain,” David said. “Nothing can grow without moisture, and it’s been drier than a popcorn fart out here.”

I drove out to David’s farm to assess the situation. When I got there, I observed the durum stand was patchy and quite a few areas had no plant growth. Because the field had been seeded two months earlier, it appeared the crop stage was significantly behind, or the seed had difficulty germinating.

Where germinated plants had emerged, many of them were turning yellow and were starting to wilt, particularly the larger three-leaf plants. I observed the plant stand was thinnest on the hilltops, and in the low spots, the crop was yellowing off in rows.

It was obvious environmental stress had taken its toll on the crop. The recent rain should’ve helped, but the plants weren’t coming back at nearly the rate they should’ve been, so I knew there had to be something else going on.

David informed me he had used a seed treatment containing an insecticide on his durum to protect it against early-season pests. When I reviewed the producer’s fertilizer program, I didn’t see any nutrients that had been applied incorrectly, so everything checked out there.

It also didn’t appear to be a herbicide issue, as the crop had been sprayed with a contact herbicide that spring and I didn’t detect any problematic residual herbicides when I looked back at the field history. The pattern of damage in the field didn’t indicate this was a herbicide drift problem either.

I dug around in the soil to see if something like a mechanical issue with the drill could have interfered with seeding, but I found enough seeds placed at the correct depth that I felt comfortable ruling this out. However, I did observe torn and ripped plant material below the soil surface, which was a puzzler at first because I couldn’t see any pests amidst the dirt that might have caused this.

Crop advisor’s solution: Struggling durum crop undermined by wireworms

The torn and ripped plant material below the soil surface was a clue. It looked like feeding damage caused by some kind of pest, but I was puzzled at first since there weren’t any insects in the dirt that I could see. When I dug a bit deeper, however, I found the source of the trouble: wireworms.

Late June was later than usual to be inspecting for wireworm damage, so the insects had moved deeper in the soil profile. That made them a little more difficult to find initially, but once I did, I could see the wireworm population was quite high.

David had treated his durum seed with insecticide to ward off early-season pests, but it had now been two months since the seed was planted. At this point, little protection remained against wireworms since a good percentage of insecticidal seed treatment would have worn off the seed and started to break down.

Unfortunately for David, there wasn’t anything he could do about the wireworms or to improve the state of his durum crop. Some of the larger plants did recover as the weather improved and the field received some moisture.

In the end, the yield was only down 20 to 25 per cent from what it should have been, which was a better outcome than either David or I would have expected given the sorry state of the crop in early summer.

The weather, of course, is outside of everyone’s control, but I indicated to David there were steps he could take to try to ensure his durum crop got off to a better start the next time around.

For one, he could avoid seeding too early in the year, and always try to seed into warmer soil with adequate moisture. He could also try increasing his seeding rate if he anticipated poor growing conditions and potential issues with pests, such as wireworms.

It will be important for David to continue to use treated durum seed since the pests had become established on the farm. I also suggested he try using bait balls to track wireworm populations in his fields in the future.

Austen Preete, CCA, AAg, works for Richardson Pioneer Ltd. in Corinne, Sask.

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