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Field-level agronomy

By Staff | Jul 22, 2016

ANGIE REICK-HINZ, an ISU Extension field agronomist, shows a group of men and women producers and landowners how to stage the growth of a soybean plant during a July 12 Agronomy in the Field for Women program at the Smeltzer Iowa Learning Farm near Otho.

OTHO – With a goal to increase women’s knowledge about agronomic production and conservation practices, Iowa State University Extension has been hosting a series of meetings titled Agronomy in the Field for Women.

The meetings began early in the spring and have covered planting conditions, replant decisions and ongoing issues such as crop growth and development, weed and pest identification and management.

It will continue through the tillage season.

Angie Rieck-Hinz has been hosting the gatherings throughout this year’s growing season.

They’ve been held at various locations, including the Northern Iowa Research Farm located near Kanawha and the Smeltzer Iowa Learning Farm located near Otho.

ERIN HODGSON, an ISU Extension entomologist, shows a group of women what signs to look for when scouting for corn rootworm damage at an “Agronomy in the Field for Women” program held recently at the Smeltzer Iowa Learning Farm near Otho.

The women met near Otho on July 12 with Rieck-Hinz and Erin Hodgson, an ISU Extension entomologist. Topics discussed with the group of landowners and producers – made up of six women and two men – included insects that should be looked for in corn and soybean fields at this point in the growing season.

Hodgson said right now would be a time to be looking for any energy by corn rootworm adults above the ground.

Although at this stage of the game, it is too late for any rescue treatment, Hodgson said looking for damage that could have possibly occurred by corn rootworms will let a producer better prepare for next year’s growing season.

“Seeing corn rootworm adults above the ground is my key to look underground,” she said.

The corn rootworm adult is very small, Hodgson added, so they may be hard to detect. One way to help look for them is to soak the plant, including its entire root system and dirt, in a bucket and they should float to the top.

Then, take a look at the roots and determine potential yield loss that can occur due to the root damage.

Hodgson strongly recommends that method, as the plant will most likely appear to be healthy above the ground, leaving producers and landowners clueless as to what has happened below ground.

“You might not see above ground that there is damage until something happens like a wind event,” she said.

No matter what insecticides, traits or rotations a producer may be using to help combat corn rootworm, Hodgson said that a producer should still walk out into corn fields and spot check for damage.

Hodgson and Rieck-Hinz stressed to the group to not fall for rescue treatment scams for corn rootworm.

“There is nothing that can be applied for corn rootworm above the ground, there is only below-ground treatment,” said Hodgson. “Don’t believe in rescue treatments, they are very unreliable.”

The rescue treatment, Hodgson explained, needs to be able to penetrate into the soil and get to the roots.

That, she said, is a lot to ask out of a product.

If a producer is seeing corn rootworm damage, Hodgson said it is imperative they do something next growing season such as using a corn rootworm trait in their seed options, a soil-applied insecticide and using a corn and soybean rotation.

“You just can’t keep doing the same thing over and over, you have to mix it up to control this pest,” she said.

Although it is highly recommended to dig up corn plants and check those roots, if a producer is unable to do so, there is a method using sticky traps that can help them determine if there is corn rootworm adults present in their fields.

As far as soybeans, Hodgson said now is also the time to be out scouting fields for soybean aphids.

“Around blooming is a time to assess for soybean aphid activity and continue to do so through July and August,” she said.

Soybean aphids do not like hot and dry weather, which has been the case in many parts of the state.

If soybean aphids are present in the field, Hodgson said the economic threshold is 250 bugs per plant. It is at that time a producer should consider spraying their field.

There are a few ways to scout for aphids.

The standard way is to gather 30 plants and count the aphids on each plant. Producers should look at the newest growing points of the plant, which would be the newest tri-foliates, and checking the underside of those leaves.

Aphids, Hodgson said, will typically stay on the underside of the leaves until there is over-crowding, then they will be present on the stems and other parts of the plant.

Another method used for scouting for soybean aphids is called speed scouting.

Hodgson said a soybean aphid will drink from the plant and excrete sugar which will make a sticky substance on soybean’s leaves.

If a producer is scouting for the aphids and their pants get sticky, that could be a sign of serious damage that has already been done to the field.

Spider mites like hot and dry weather, Hodgson said, and it is also time to be scouting for them.

She recommended tapping the leaf onto a piece of paper and watch for what will look like dust to move around on the paper.

These insects will cause stifling or discoloration of the plant in hot and dry weather and that could be an indication it is time to spray.

“It’s a judgment call when it comes to spider mites,” said Hodgson. “Just don’t confuse stifling and discoloration with a disease. It could be spider mites.”

If a producer sees these insects in their field, Rieck-Hinz advised to not spray unless the counts are meeting the economic threshold.

“If it is not at the economic threshold, you are only ramping up the chance to bringing resistance and we only have so many products out there,” she said.

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