Crop advisor casebook: Why are these pea pods scratched and shredded open?

A Crop Advisor's Solution from the March 24, 2020 issue of Grainews

Tyneal Welter. photo: Supplied

Brian is a grain farmer who also runs a successful crop input and agronomy business near Humboldt, Sask. He regularly calls or drops by my office with questions or ideas, so I wasn’t surprised when Brian came in to see me late last July.

After shaking my hand, Brian got right down to business, pulling a handful of pea pods out of his pocket to show me. All of the pods were scratched up and some were shredded open.

“What do you think?” he asked. “I haven’t seen this type of damage before in my yellow field peas, but I think some kind of insect or animal must have caused it. Raccoons, maybe?”

Brian suspected raccoons because it was only the pea pods at the top of the plants that had suffered any damage. “They stand up on their back legs to eat,” he said, “and that could explain the scratch marks.”

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I thought racoons were a possibility, but I told Brian I’d need to check out the yellow pea crop on his farm to be sure.

Once at the field, I observed the pea crop was at the R4 stage — most of the pods on the plants were done filling, but they hadn’t started to ripen yet. Brian pointed out there were numerous patches of damaged plants spread randomly around the field, the largest were on the headlands and smaller ones were spread throughout the crop.

Brian and I walked out into the headland where the crop injury appeared to be the most severe and I could see while some plants were severely affected, there were others that appeared untouched. In addition, only the top parts of the pea plants were damaged, and it was only the pods that were affected.

All of the pods were scratched up and some were shredded open. Some pods had damaged or missing seeds, but we didn’t see the missing seeds on the ground near the base of the damaged plants. Only the top of the affected plants were damaged, and only the pods were affected. photo: Supplied

The plants with the most damage had numerous scratched and torn pods and there were even some pods that had damaged or missing seeds. Curiously, we didn’t see any of the missing seeds on the ground near the base of the damaged plants. The pods with the least damage showed only small specks of necrosis.

It looked to me like some kind of critter had to be responsible, since a weather event or mechanical damage couldn’t explain these symptoms.

Brian and I searched the ground for raccoon paw prints but couldn’t find a single one. There were no signs of any other animal tracks either.

“Maybe it’s something else?” Brian asked. “Could it be some type of insect feeding on the pods, like grasshoppers?”

I pointed out to Brian we hadn’t seen any grasshopper cocoons, pupae or adults in the areas with the damaged pea plants, or noticed any other harmful insects for that matter. The answer had to lie somewhere else.

Crop Advisor’s Solution: Blackbirds to blame for pea damage

It was now getting late, so Brian and I agreed to call it a day and come back to the field the following morning. We were in for a bit of a surprise the next day when we saw a flock of blackbirds that appeared to be feeding in one area of the field.

Brian thought at first the birds could be consuming caterpillars or some other kind of insect feeding on the pea pods, but it turned out the birds themselves were causing the damage we thought could be the work of raccoons.

The birds perched themselves on the top of the pea plants, using their beaks and claws to tear the pods open to feed on the small, fleshy seeds. They weren’t feeding on the bottom parts of the plants — our theories were perhaps they preferred to stay on top of the canopy or that the seeds in the lower pods were too firm for their liking.

We had our answer as to what caused the damage in Brian’s yellow pea field, but at this point in the season there wasn’t much that could be done about it. We knew the pods would be fully ripened soon, making them less susceptible to the damage caused by the blackbirds.

Fortunately for the grower, the damage was limited to small areas within the field, but within those areas, the yield loss was significant — Brian informed me later that while harvesting the crop, the yield monitor on his combine registered a reading at or near zero in those patches with the blackbird damage. This was likely due to the loss of seeds the birds had fed on, but also increased shatter due to the seemingly mild damage to the pod.

Going forward, Brian will be on the alert for blackbirds and he now knows what kind of damage they can inflict on pea crops and at what crop stage to scout at. He’s also going to start using a scarecrow or a scare cannon in his yellow pea fields, which could provide some measure of protection against blackbirds in future years.

Tyneal Welter, CCA, PAg, works for Richardson Pioneer Ltd. in Humboldt, Sask.

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