Update on soybean gall midge09/11/2018 | Crop Production Research, Soybean News
By Scott Nelson, On-Farm Network® Director
The gall midge has become an economic pest of soybeans in Iowa and beyond. It has been found in soybeans in the western third of Iowa, eastern Nebraska and eastern South Dakota. There have been no reports of this pest in central or eastern Iowa, but farmers are encouraged to look for symptoms.
The gall midge is a small fly, about 1/16th of an inch in size. It is characterized by hairy wings, long legs and a long ovipositor. There are many species of midges and the soybean gall midge adult is difficult to identify even by expert entomologists.
Currently, not much is known about the insect, but scientists are actively researching and reporting what they’ve learned so far.
The first recognition of the pest was in eastern Nebraska in 2011. In 2015, it was found in northwest Iowa, eastern South Dakota and eastern Nebraska. Gall midge populations increased in 2016 to the point of significant soybean yield reductions. The pest grew in intensity in 2017 and became widespread in 2018.
Gall midge adults have been found on yellow sticky card traps in soybean fields, but entomologists prefer to use emergence cages to collect adult flies. It is important to note that while the adult gall midge does not feed on soybeans, the orange-colored larvae feed on the soybean stems, causing severe destruction and often whole plant death.
Scientists believe the life cycle of the gall midge is as follows:
- Larvae overwinter in the soil.
- After pupation in the early spring, adult midges emerge and lay their eggs at the base or lower stems of soybean plants.
- The eggs hatch and the larvae feed on the stems. Based upon observations, there appears to be two to three overlapping generations per year.
- For the hessian fly, a cousin of soybean gall midge, the life cycle from egg to adult is about four weeks. In some observations, the first generation of soybean gall midges were found on 3-inch soybeans.
No consistent patterns in planting dates, crop varieties, presence of cover crops, tillage or row spacing have been found that affect the insects’ population growth or decline.
Insecticide seed treatments have not shown to be effective. Some researchers believe that higher rates of insecticide seed treatment could offer some suppression, but these high rates of seed treatment are not currently offered and there is no scientific data to support their effectiveness. Some farmers observed that fields treated with a foliar insecticide had a lower incidence of soybean gall midge, but this has not been verified in controlled studies.
Over the next several months, entomologists and crop protection professionals will be diligently working on potential solutions for 2019 production. Although not proven, here are some points to consider for control of gall midge in future production:
- Monitor for presence of the fly the first four to eight weeks after planting. This can be done with sticky traps or emergence cages. Note that the fly is difficult to identify and will require use of a hand lens and a detailed guide on how to identify the pest. This guide will be produced before spring of 2019.
- As soon as soybean gall midge adults are identified, apply a foliar contact insecticide. Since adults do not feed on soybean plants, longer lasting residual insecticides are not necessary. These applications could occur on field edges, as the midge attacks there first.
- The hope is that a single foliar application of insecticide could provide sufficient suppression of soybean gall midge. However, it may be necessary to do two applications.
- Entomologists do not think that insecticides have any effect on the larvae, as they feed inside the soybean stems. Control options must be focused on adult flies.
Not all foliar insecticide labels will allow for application for control of soybean midge. Researchers and insect experts are working with crop protection companies to develop emergency use labels on insecticides that could have suppressive activity of the pest.
Research will be ongoing in 2019. Some of the testing will include insecticide efficacy in one- and two-pass programs as well as for higher rates of seed treatment. To do this work, we are looking for volunteers to conduct on-farm research with ISA. Contact firstname.lastname@example.org to participate.
Scott Nelson can be reached at email@example.com
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