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Crop advisor casebook: A thin lentil crop due to seeding problems?

A Crop Advisor's Solution from the February 12, 2019 issue of Grainews

Austen checked the plants for root rot in all areas of the field. All plant roots were healthy, which allowed me to rule out root rot. Because the plants were asymptomatic, Austen also struck rhizoctonia off the list.
Austen Preete. photo: Supplied

Colin farms 6,000 acres of canola, lentils, durum and canaryseed south of Regina, Sask. He called me at the beginning of June about his poor lentil stand. He said the stand looked less vigorous than it should. He thought the problem might be related to seeding.

“I must’ve messed up during seeding. Maybe I put them too deep, or perhaps I cut back too much on my seeding rate,” he said. It was a good time to pay Colin a visit.

At the field, the lentil stand was thinner in some areas of the field than others. Along the rows, there were blank spaces where there should have been lentil plants. The areas of missing plants occurred randomly throughout the field.

Plant growth and development in those areas of thin stands were affected, with some plants being stunted and up to three or four nodes behind the others in the same row. These damaged plants appeared to have emerged later than the others. All lentil plants should have been out of the ground with a handful of nodes by that time of year.

In the unaffected areas, the rest of the lentil crop looked relatively healthy.

To put Colin’s mind at rest about a seeding error, we checked his seeding depth and rate as well as his equipment. Both his seeding depth and rate looked good and his equipment was working fine. The patchiness of the affected areas didn’t suggest there was an issue at seeding.

Last year was the 100-year drought for this area. Germination issues were a common occurrence, but usually other crops were affected and not lentils. Since Colin seeded early into adequate moisture, we suspected this wasn’t the issue. After crop emergence, conditions were dry, but it was early enough in the season that the lentils weren’t suffering from moisture stress yet.

Colin seeded the lentils at just over one bushel per acre which was enough seed to reach his target plants per square foot.

The majority of the lentils looked healthy and weren’t showing any signs of nutrient deficiencies or imbalance. Colin’s fertility records and rates revealed adequate nutrient levels and correct application rates. He had seed-placed 40 pounds per acre of 11-52-0 (monoammonium phosphate) fertilizer as well as granular inoculant.

Due to the dry conditions, it was unlikely disease was a factor as the environment wasn’t conducive to infection or disease growth. Additionally, there were no visible lesions on any plants. The plants were also free from chlorosis or any yellow discolouration.

Since it had been an issue in the past, I checked the plants for root rot in all areas of the field. All plant roots were healthy, which allowed me to rule out root rot. Because the plants were asymptomatic, I also struck rhizoctonia off the list.

One pest that can cause thin plant stands like this is cutworm. I had already checked this field for cutworms earlier in the year and found none. If it was cutworms, it was strange the symptoms were more noticeable now, rather than earlier in the spring when cutworms are more prevalent. Perhaps I missed them the first time I scouted?

I dug in the soil for what seemed like hours — no cutworms!

Crop Advisor’s Solution: Wireworms, not cutworms, were the culprits in Colin’s lentil field

After eliminating many other factors, I thought I may have missed cutworms when scouting the field earlier that spring. I didn’t find any cutworms; however, while digging up stunted lentil plants, I noticed some had insect damage directly above the seed.

Some shoots had been completely chewed off and were irreversibly damaged. The damaged plants that emerged were chewed below the soil surface, and emergence was delayed slightly compared to undamaged plants. After closer examination, I found the seeds had been chewed on — small pieces were missing from the seeds and in some cases the seeds had been completely hollowed out, leaving only the seed coat.

With a spade, I dug deeper into the soil and, much to my surprise, there was the elusive pest we were looking for — wireworms!

At that point in the growing season, the damage had already been done and there was nothing Colin could do about the wireworm infestation in his current lentil crop. That being said, Colin will choose a seed treatment containing insecticide to help control wireworm populations in the future.

For growers concerned about wireworm infestations, bait balls are useful tools that can be used to monitor pest population levels for upcoming seasons. Bait balls will indicate the areas of greatest concern for insect damage, and growers can avoid blanket applications across entire fields, which harm beneficial insects as well as wireworms.

The slight yield loss at harvest was directly attributed to the missing plants and the damaged plants that emerged late and never produced viable seeds.

Although wireworms are usually only considered problematic in cereal crops, they can also be destructive in pulses. Using insecticide seed treatments as well as monitoring and recording wireworm population levels will help keep these pests in check.

Austen Preete works for Richardson Pioneer Ltd. in Wilcox, Sask.

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