New Soybean Pest Persists

LEWIS, Iowa (DTN) -- Soybeans farmers in southwestern Iowa are engaged in a frustrating battle with a new pest called soybean gall midge. Last week concerned growers gathered at the Iowa State University (ISU) Armstrong Research Farm near Lewis, Iowa, to learn more about the insect.

Erin Hodgson, ISU Extension entomologist, said concrete answers on how to stop the tiny, yield-robbing pests are still few and far between. The gall midge was first reported in 2011 in Nebraska and has spread in both intensity and distribution. In Nebraska, some call the pest orange gall midge.

The gall midge begins life as a small, fragile fly that goes through a complete metamorphosis (egg, larva, pupa, adult). Females appear to lay eggs into the base stems of soybean plants. The resulting orange colored larvae feed on the vascular tissue within the stem, weakening plants and lowering yields, Hodgson said.

In some cases, plant injury is not overly obvious -- the plants may initially simply turn a lighter shade of green, she noted. Early feeding begins fairly close to the ground and continues to move higher on the main stem of the plant. Eventually severely infested plants die prematurely and easily snap off at the soil surface.

What makes the pest more challenging is the gall midge appears to have two to three overlapping generations per year. "They appear to be weak flyers, only moving as far as they have to, to lay their eggs," Hodgson said. The pest typically infests the edges of the field first.

The pests are puzzling as they have not shown a consistent pattern, she said. They have been found in soybean fields with different row spacing, tillage, fertility and seed genetics.

Right now the gall midge is thought to be distributed in 18 western Iowa in counties along the Missouri River, according to Hodgson. Areas of Nebraska, South Dakota and Minnesota have also reported issues with the pest this year.

Hodgson said most likely the gall midge will spread to other areas such as central Iowa in the coming years.

FARMER FEEDBACK

Ryan Rusk, a farmer and seed dealer from Linn Grove, Iowa, said the gall midge issue in Buena Vista County doesn't appear to be as bad this year as it has been over the previous two years in his area.

"There are some who wonder if they overwinter in the soil," Rusk said. "But we rotate crops and they are still in the beans at the edges of these different fields."

Fred Halverson, who also farms near Linn Grove, Iowa, said he has seen the pest take a toll on his soybean yields. Last year he watched the yield monitor register zero on the first pass of the combine in one 55-acre field. The second swath of the 25 ft. grain platform recorded a yield of 20 to 30 bushel per acre. It wasn't until the third pass -- about 75 ft. into the field, that the monitor began to show what the field ultimately averaged -- about 55 bpa range.

Farmers attending the meeting peppered Hodgson with questions, but she cautioned that scientists are still in the investigative stage with the pest. Was weather to blame? Hodgson doesn't think so, as some growers struggling with the pest had dry growing seasons, while others had wet weather.

Killing adult female gall midge before they lay the eggs into the base stem of the plant would seem a logical solution, but Hodgson said that strategy hasn't proven effective. You might kill some adults, but she noted that there would still be other females flying about and nothing can touch the larvae once in the stem.

Hodgson was asked if planting all corn might be an answer. While she was not advocating that as a practice, this could be a short-term management solution, she said.

In the past, there have been parallels drawn between hail damage and gall midge. However, Hodgson said many fields in western Iowa that have gall midge present this year did not have hail events.

Hodgson added that gall midge appears not to have any natural enemies. So why is the problem showing up now? "Pests take advantage of what is available to them and the state of Iowa has many acres of soybeans available to them," she said.

Growers are being advised to contact Extension educators if they see evidence of gall midge to help gain more information of the scope of the pest.

More information on this pest can be found here:

https://cropwatch.unl.edu/… https://crops.extension.iastate.edu/…

http://blog-crop-news.extension.umn.edu/…

Russ Quinn can be reached at russ.quinn@dtn.com

Follow him on Twitter @RussQuinnDTN

(PS/CZ)

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