Apr 1, 2019

Controls curtail bird damage in sweet corn

Sweet corn fields nearing harvest hold much promise – for birds as well as growers.

“We asked our sweet corn growers what is their biggest pest issue. Eighty-four percent said birds,” said Marion Zuefle, Cornell University vegetable integrated pest management Extension area educator. Zuefle was a speaker in the sweet corn session of the recent Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids, Michigan.

“Not only are birds coming in and feeding, they’re putting droppings everywhere and that’s a food safety concern,” Zuefle said. “Most of our growers are fresh market. They sell sweet corn at a roadside stand and contamination is a big issue.”

Four methods of bird control were recently evaluated in a three-year study at Cornell. The methods are a chemical deterrent, balloons with scary eyes, an air dancer and de-tasseling.

Avian Control Bird Repellent was the chemical deterrent. The active ingredient, methyl anthranilate, is a grape seed extract. “The birds feed on it and it causes irritation in their mouths and eyes, and they’ll fly away,” Zuefle said.

Methyl anthranilate must be applied two weeks before harvest and before the birds find the sweet corn and start to feed. It must be re-applied every six to eight days or sooner if it rains. It has a four-hour re-entry interval (REI) and a zero preharvest interval (PHI). “A zero PHI is good for fresh market growers,” Zuefle said.

Balloons with scary eyes and attached tails or strings move in the wind and imitate the image of a predatory bird. They’re inexpensive, mounted on stakes and easy to move. “Birds are smart,” Zuefle said. “They get used to what’s going on in a field so control measures need to be moved around.”

An air dancer is an inflatable figure made from a tall, brightly-colored, air tube. It rapidly and repeatedly deflates and re-inflates on a pre-set timing and the random movement scares birds.

An air dancer requires a generator or other source of electricity. “The power source is a big issue,” Zuefle said.

De-tasseling involves cutting off the sweet corn’s tassel and upper leaves after pollination. “It’s to prevent the birds from perching,” Zuefle said. “They like to perch on the tassel but not down on the leaves.”

De-tasseling is labor intensive if done manually and mechanized options are expensive.

The study results were strongly impacted by bird behavior. The red-winged blackbird had by far the highest numbers of any bird observed at the study sites and appeared in flocks numbering in the hundreds of birds.

“When red-winged blackbirds start flocking, it means they’ve stopped breeding and are eating before migration,” Zuefle said.

The overwhelming numbers of blackbirds settled on multiple plots at the same time and the differences between control methods were often not statistically significant.

However, once deterrent tools were placed in a plot, birds tended to avoid the research site and look for other sweet corn fields. The damage in some of the off-site sweet corn fields ranged from 15 to 50 percent and was much higher than the damage in the study’s untreated plots.

“Our growers are very excited about these tools,” Zuefle said. “They plan to use one, two or all of them – even though our conclusions weren’t all that clear.”

Control tactics must be put in place before the birds arrive. “Once they find the food source, it’s hard to get them to move,” Zuefle said.

— Dean Peterson, VGN correspondent