Sunday, April 22, 2018
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Reining in rootworms

Battling beetles needs more weapons than built-in seed resistance.

Dubbed the billion-dollar bug because of damage caused by this pesky pest, rootworms are no laughing matter to corn producers.

Each year, the larvae of the tiny beetle typically costs farmers an estimated $1 billion, according to U.S. Department of Agriculture officials.

About $800 million is reported in yield loss and $200 million in treatment expenses.

Monsanto, developers of a corn rootworm-resistant seed hybrid that is genetically modified and other seed developers, have recently come under fire because of reports that the insects are developing tolerance to the toxin in the seed.

Chandler Mazour, manager of the Monsanto Water Utilization and Learning Center south of Gothenburg, said the beetle-like bug has always been a significant problem in the area as well as in other places where corn is grown.

Monsanto sales and technical employees are educating farmers about what to do, he said.

“It gets down to working with farmers with the different options that are available,” Mazour said.

But first, the nature of the western corn rootworm must be understood.

After rootworms mate in late summer, he said the adults lay eggs in the soil. The eggs live underground and hatch in late May and June, when rootworm larvae begin nibbling the roots of young corn plants.

What larvae eat affects the plant’s inability to draw up water and nutrients, Mazour said, which stunts development. Damaged plants have difficulty remaining upright—especially in strong wind.

To stop the insect from eating corn roots, Mazour said Monsanto has introduced three rootworm-resistant seed hybrids in 2006—VT3, VT Triple Pro and Smartstax.

Bt (genetically modified) proteins, produced by the hybrids, fit specific receptors in a rootworm’s stomach and kill the insect, he explained.

Mazour said seed selection for farmers comes down to which hybrid works better in a particular field.

In areas where rootworms are difficult to control, Mazour said farmers are also encouraged to rotate crops to break the rootworm-eating cycle.

If growers use Bt technology, he said they are also required to plant a non-genetically modified corn which is known as plant refuge in the agriculture industry. This practice helps slow down the development of resistant insects.

Farmers plant a certain portion of their field (Bt corn hybrids require 20% refuge)with seed that doesn’t have in-plant protection.

Planting a refuge allows some target pest insects to feed, mate and reproduce without being exposed to the Bt trait, Mazour said.

When this happens, the worms won’t be resistant to the hybrid. Without a refuge, Mazour said rootworms exposed to Bt corn each growing season eventually become resistant to the hybrid.

Mazour said mating between Bt-susceptible insects from the refuge and potential resistant insects may ensure that susceptibility to the Bt toxin passes on to the next generation.

“We insist on this because it’s the best things for protection of technology and the producer’s ability to make money,” he said.

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