The goal of this proposal is to improve the understanding of short- and long-term changes in the insects and pathogens affecting Minnesota soybean production, their impact on soybean yields, and the profitability of management practices for Minnesota soybean farmers. This project continues previously funded work and contains two objectives addressing different aspects of this goal.

Objective I. Evaluate insecticide and fungicide efficacy in an ongoing and systematic way
Long-term pesticide evaluations provide a tool to monitor changes in yield response and disease/pest populations over time.
a ) Evaluate foliar fungicide effects on soybean disease and yield on at three southern MN locations. Many fungicide efficacy studies conducted by academic and industry researcher are designed to find positive results under conditions favorable for development of a specific disease (susceptible genetics, inoculated, irrigation, etc.). On the other hand, growers often need to make fungicide decisions with limited knowledge of variety susceptibility and/or presence and severity of soybean diseases. These studies will be conducted under typical growing conditions and simulate potential responses in the environments of commercial fields.
b) Support continued evaluation of insecticide compounds on soybean pests such as the soybean aphid. Pyrethroid resistant aphids and the revocation of crop tolerances for chlorpyrifos has limited the available insecticide tools for soybean. We will continue to evaluate the remaining insecticide options for soybean aphid control and at the same time monitor field-evolved insecticide resistance.
Objective II. Define the distribution and host range of the soybean gall midge within Minnesota.
The soybean gall midge (SGM) is a new pest of soybean in Minnesota. High population densities can cause 100 % yield loss on field perimeters with lower losses extending well into field interiors. This objective will continue previous work to evaluate the risk of this insect to MN soybean production.

a) Track changes in distribution of soybean gall midge across Minnesota environments
We will continue to survey SGM to determine if it is expanding its range or increasing the severity of injury in MN. Since 2018, SGM infested fields have been found in an increasing number of counties. Most infestations have been very low population densities with little crop damage. It not known if this insect is native, is introduced and expanding its geographic range in MN, or if overall population densities and injury to Minnesota soybean will remain low. We will survey counties where SGM has not been confirmed. We will also continue to survey several counties with a history of SGM infestations to track changes in crop injury. These surveys will help determine the distribution of SGM understand the risk it poses to MN soybean production.
b) Examine alternative hosts and determine if additional Minnesota crops are at risk
We will conduct a host preference study of annual legume crops and examine commercial dry bean fields and native prairie plants for SGM infestation. The SGM has been found on sweet clover and alfalfa in addition to soybean, but its host range is unknown. To identify other crops that may be potential hosts, we will place greenhouse-grown, potted annual legumes (soybean, dry bean, broad bean, cowpea, etc.) in commercial soybean fields when egg-laying adults are active. After two weeks, plants will be dissected for presence of SGM larvae. Dry bean fields in geographies where SGM have been confirmed will examined for the presence of SGM larvae. SGM might be a native insect. Therefore, native legume species will be examined for the presence of SGM larvae in western MN wildlife areas.

• Through coordination with MN soybean, a written description of the projects will be available through MN Soybean communication channels during spring 2022. Spurred by MN Soybean and University of MN Extension communications, we anticipate these projects and potential benefits to growers can also be discussed via traditional ag radio broadcasts (e.g., Linder farm network, Brownfield, and local)
• Reporting single year results can be problematic for studies where variable environments or pest populations can produce different results in subsequent years. The data generated from the project should not suffer these constraints. Any fungicide and insecticide data generated by this project will have a significant set of historical data (previously funded by MSR&PC to provide perspective. The soybean gall midge (SGM) distribution and alternate host data can be viewed as a refinement of current knowledge.
• Where treatment differences are visible, we will hold field and/or video tours of gall midge and fungicide research sites during late summer 2022.
• Preserved specimens of soybean gall midge larvae and their injury will be available at ROC field days, UMN field school, and at Extension or MN soybean booths at Farmfest, and possibly other ag events.
• During late fall 2022/winter 2022-23, written results of fungicide and insecticide experiments will be distributed through SW MN IPM Stuff, MN Crop News. An effort will be made to include information from these studies in ag media presentations. A display presentation will be prepared for MN Ag Expo.
• Research results will be available for presentation at crop Pest Management Short Course, Research Updates, ROC winter Crop Days, and additional UMN and MN Soybean events.
• As they occur, new county observations on SGM will be reported via MN Extension, MN soybean, and ag media. Distribution data will continue to be collated and archived at the soybeangallmidge.org website. Low SGM populations during 2021 limited opportunities to update education materials. Depending on 2022 SGM populations, new images will be used to update MN Extension SGM fact sheets and videos

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Project title: Soybean pest management research – SW MN 2022

Objective I. Evaluate insecticide and fungicide efficacy in an ongoing and systematic way.
I a) Foliar Fungicide: This project continued long-term studies in southern Minnesota to determine the value and efficacy of standardized foliar fungicides on soybean moisture and yield. Study sites were located at three University of Minnesota Research and Outreach Centers (ROCs). These sites were not selected on the expectation of soybean disease (white mold, frogeye leaf spot, etc.). At each site, two foliar fungicides were compared with an untreated control on three unrelated soybean varieties.

Not unexpectedly, moisture and yield differed by study location and moisture differed by variety. We did not detect significant yield differences among the three fungicide treatments at any site or overall. All study sites saw low levels of foliar disease. With the inclusion of this 2022 data, foliar fungicide application provided a significant yield benefit for fungicide in only 53% of 19 site years (2016- 2022). Dry 2021 and 2022 site years dramatically reduced the overall probability of fungicide response.

b) Soybean aphid foliar insecticide: In a SW Minnesota study, thirteen foliar insecticide treatments were applied on August 10 to early R5 stage soybeans. Aphid populations were rated at 0, 5, 7, 15, and 21 days after application.

Dry weather after insecticide application affected the development of both soybeans and aphids. Insecticide applications did not impact yields due to few cumulative aphid days (< 7,000) in untreated plots. Although most insecticides performed well, bifenthrin and lambda-cyhalothrin insecticides applied alone accumulated more aphid days than other treatments. These results, combined with reports from 2022 farm fields, indicate a portion of the soybean aphid population in this area remains resistant to pyrethroid insecticides. Insecticide resistance should be accounted for in grower’s soybean aphid management plans.

Objective II. Define the distribution and host range of the soybean gall midge (SGM) within Minnesota.
a) Soybean survey: Eighty-six fields were surveyed in 2022. No new SGM infested MN counties were identified during surveys of counties adjacent to those previously found to be infested. 2022 SGM larval populations were not detected or were apparently lower during in several surveyed counties previously found to be infested.

b i) Dry edible bean survey: Dry edible bean fields in four West Central Minnesota counties with known SGM infestations were surveyed. Two SGM-infested navy bean fields were found in Lac Qui Parle County on 8/12/22. Soybeans near these navy bean fields were also infested and at a higher rate. These fields represent the first report of SGM infestations of bean (Phaseolus vulgaris) in production fields. Yield losses from SGM in Phaseolus crops have not been documented, but dry bean growers should be aware of potential field edge injury from SGM larvae in areas where SGM occurs on soybeans.

b ii) Prairie legume survey: It is unknown whether SGM is an introduced insect or a native that is adapting to soybean as a host. Potential native prairie legume hosts (lead plant, prairie clover, tick trefoil, etc.) were examined in roadsides and wildlife areas in these same WC MN counties as well as Rock, Lincoln, and Cottonwood counties in SW MN. SGM larvae were not observed on prairie legumes during 2022.

b iii) Sentinel plants: Mobile sentinel plants were used to examine whether SGM could attack annual legume crops other than soybean. Eighteen annual legumes were greenhouse-grown in four-inch pots and used as sentinels. The potted plants were placed in a soybean field for one week when the overwintering and 1st generation adults were active (June 14 and July 18 respectively). The plants were moved back to the greenhouse and after a week their stems dissected for SGM larvae.

SGM larvae from overwintering adults were found in three soybean varieties. SGM larvae from 1st generation adults were found in the stems of the three soybean varieties, four of the seven bean (Phaseolus vulgaris) cultivars, and lima bean (Phaseolus lunatus). Bean and lima bean represent two new SGM hosts! The bean and lima bean sentinel plants had a lower percentage of infested plants than soybeans and except for lima bean fewer larvae/plant. Lower infestation rates compared to soybean were also noted in Lac Qui Parle commercial navy bean fields.