Crop advisor casebook: What’s taking a bite out of this producer’s wheat crop?

A Crop Advisor's Solution from the April 24, 2018 issue of Grainews

The seedling leaf tips were notched in this Alberta producer’s wheat crop. 
In addition, the leaves had holes, giving them a shredded appearance.
Brianne Birch. photo: Supplied

While scouting his wheat crop at the end of May last year, Alex noticed some seedling leaf tips were notched. Also, the leaves had holes, giving them a shredded appearance.

Alex farms 3,000 acres of barley, wheat, canola and peas near Manning, Alta. Alex thought the damage he found in his wheat crop was caused by insect feeding, but he didn’t know what pest had infested the field.

“Could it be flea beetle or cutworm damage?” he asked.

By the sound of it, Alex had an insect pest problem in his wheat crop. I headed out to his farm that afternoon to check it out.

At the field, I scanned the crop for a feeding pattern. For example, was the damage located in patches throughout the field or around its perimeter? In this instance, most of the damage was concentrated at the field’s outer edges.

Although adult flea beetle feeding can damage plant seedlings early in the growing season, on wheat the damage is characterized by pitted stripes on the leaf surface running in the direction of the veins. Thus, the leaf-shredding damage in Alex’s crop was not caused by flea beetles.

Cutworms cause chewing damage to leaves, such as holes or notches. To determine if cutworms were eating the wheat seedlings, I returned to the field that night to scout for the insects since they are nocturnal.

I dug into the soil about one to two inches below some damaged plants. I didn’t find any cutworm larvae or evidence of cutworm activity, such as stems severed below the soil surface. Also, the pattern didn’t fit because cutworm damage usually occurs in patches.

It was the following day, during the heat of the afternoon sun, that I caught our pest in the act.

Crop Advisor’s Solution: Get the jump on those pest grasshopper populations

It was hot and sunny the following afternoon when I returned to the field to search for my insect pest. While I was examining some plants at the field’s edges, I found what I was looking for — grasshoppers! Particularly, migratory grasshoppers (Melanoplus sanguinipes) in the nymph stage, which were feeding on wheat seedlings.

Grasshopper damage is often concentrated around a field’s perimeter. Grasshoppers can cause notches on leaves, as well as holes and leaf shredding.

Since many grasshopper species can be present in one field, correct identification of pest grasshoppers is important — some grasshoppers damage crops while others do not. A producer not familiar with pest grasshopper species can consult a crop advisor for proper identification and control methods.

Chemical grasshopper control may not be needed if pest grasshopper populations don’t exceed economic thresholds. Alex chose to spray his wheat crop with insecticide because populations exceeded the economic threshold.

It’s best to spray insecticide during the nymphal stages, as adults are harder to kill than young grasshoppers. The insecticide Alex applied to his wheat crop helped decrease grasshopper populations in the field.

Cultural control methods, such as early crop seeding and crop rotation, are additional tools to help keep economically damaging grasshopper populations down. Online pest monitoring and forecasting models are also valuable tools for predicting and, ultimately, controlling pest grasshopper populations.

Detailed, yearly grasshopper forecasts are available on Manitoba, Saskatchewan and Alberta provincial agriculture websites. An integrated approach to pest management increases producers’ odds of keeping grasshopper populations below economic threshold levels.

Although pest populations in Alex’s wheat crop warranted chemical control, because the problem was diagnosed before the grasshoppers did significant damage, yield was marginally affected.

This growing season, Alex can get the jump on grasshopper populations in his fields by introducing integrated pest management practices as well as checking out the 2018 grasshopper forecast.

Brianne Birch works for Richardson Pioneer Ltd. in Manning, Alta.

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