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.
One objective of this work is continued long-term evaluation of soybean management strategies by a) Testing foliar fungicide and insecticide efficacy in a systematic way and b) Monitoring changes in pest populations over time.
A second objective is to further define the potential for soybean gall midge (SGM) damage to Minnesota soybean, and other crops by a) Conducting a host preference study to further determine the host range of the SGM and b) Continued survey to continue to determine the distribution of the soybean gall midge and its economic impact in Minnesota.
This proposal continues work previously funded by the MN Soybean Research and Promotion Council from 2016-2019 and the soybean gall midge objectives build on work funded by the North Central Soybean Research Program. This Minnesota SGM research will be coordinated with related research in other states.
This proposed project aligns with the mission statement of the MSR&PC Production Action Team and addresses the following categories:
2. Soybean Pest Management:
• Soybean Farmers need research into managing against yield and quality limiting effects of foliar diseases and root and/or stem rots….
• Soybean farmers need continued research into cultural, chemical and biological control mechanisms for management of insects including, but not limited to soybean aphid, Japanese beetles and soybean gall midge.
• Soybean Farmers need research into soybean aphid resistance to insecticide, treatments and develop alternative treatments, cultural, and other management options as/if those resistant populations are identified.
• Soybean Farmers need management strategies that deal with new or acute infestations of insect pests such as spider mites, bean leaf beetle, brown marmorated stink bug, etc.
Background
Reliance on single management tactics for crop pests and the ‘insurance’ application of pesticides and host plant resistance genes has selected for management-resistant weeds, insects, mites, plant pathogens and nematodes. Additionally, new soybean pest problems continue to emerge, and old pests become unexpected problems under favorable environmental conditions.

Are pesticides declining in efficacy against additional pests but not yet showing field -scale failures detectable by growers? Is frogeye leaf spot increasing in prevalence in Minnesota or are we just being more observant? How much are soybean pests reducing yield? How often do pesticide applications pay and under what environments? Can we develop a system that will help answer these questions? Previous research funded by MN Soybean Research and Promotion Council has begun to supply answers to these questions (e.g., Foliar fungicide decisions for corn and soybeans).

Together, the goal of the following studies on insects and plant disease is to improve understanding of how plant disease and insects affect yields, profitability and management practices of Minnesota soybean growers by examining 1) The efficacy and potential economic benefits of pesticide applications and 2) Short and long-term changes in the insects and pathogens affecting Minnesota soybean production.

Objective I. Evaluate insecticide and fungicide efficacy in an ongoing and systematic way (Team: Bruce Potter, Dr. Dean Malvick, and Dr. Robert Koch with additional University and Industry collaboration).
Justification: We will refine and implement standardized foliar fungicide trials in soybean and evaluate insecticides for control of the soybean aphid, soybean gall midge and, dependent on infestation levels other soybean pests such as two spotted spider mites.

Soybean growers and their advisors are faced with a bewildering array of information from many sources and it can be hard to separate science from marketing. Growers are most concerned with whether a pesticide treatment will pay but this, however, is not easy to answer with individual trials. Yield impacts from pesticide applications can change as pest populations change with environmental conditions and tolerant or resistant populations of pests and disease are selected.

This project will help insure new and existing compounds continue to be tested in multiple MN environments. Adding treatments or additional assessments to short-term ag-chem industry sponsored protocols often improves the value of the study for growers. A recent example would be a soybean gall midge insecticide study providing information on how the timing of plant death relates to yield loss.

Standardized trials over time, will provide growers the data to better understand odds for a return on pesticide investment. Examining long-term pesticide trial data can provide information on yield impacts by disease and insect pests. Finally, long-term results can provide evidence that pest susceptibility has changed.

The short-term funding and appropriate pesticide compounds are not always available for rapid implementation of efficacy studies on sporadic pests (e.g., two-spotted spider mites). Pesticides can be prepositioned through cooperation with industry. This project addresses the potential shortcomings in travel and labor.

Additionally, this work will complement the insecticide resistance and screening proposal work conducted Dr. Robert Koch. It will provide access to aphids exposed to known insecticide applications.

Methods:
1) Core fungicide treatments will be implemented at Research and Outreach Centers located at Lamberton, Waseca and Rosemount. Tentatively, small plot treatments will consist of a two-way strobilurin + triazole fungicide and up to two, three-way fungicides mixture applied to three soybean varieties at R3 in a factorial design with four replications. Individual 10’x30’ plots will be planted in four 30-inch rows at 160,000 seeds/acre and will be taken to yield. Plots will be rated for insects and disease at approximately V3, R3 and R6 stages.

2) MN SR&PC Funding requested for insecticide studies is to supplement funding from other sources, e.g., industry. Soybean aphid insecticides will be evaluated in SW Minnesota, preferably at the SWROC. This location site has a data history from 2003 to present. Insecticides will be applied to soybean aphid populations at economic threshold levels.

Soybean gall midge insecticide applications will be evaluated within the infested border of a farm field in SW Minnesota.

When reasonable accessible, other significant soybean pests could be addressed where they occur.

Objective II. Monitor soybean pests and pathogens both short and long-term. (Team: Bruce Potter, Dr. Dean Malvick)
Justification: A robust system to effectively track changes and occurrence in soybean pest and pathogen populations, over time, does not currently exist in Minnesota. Yield loss and risk estimates, based on perceptions, but without empirical data, may lead to research energy spent on the wrong pest problems and to growers making poor choices when selecting varieties. Data from random surveys of commercial fields may be difficult to interpret because often, host plant resistance genes and pesticide applications are unknown in the sampled fields. This project will collect and manage historical data on soybean disease and insect pests in Minnesota.

Methods
1. Based on consultations with the soybean breeding project and seed industry, soybean varieties (up to 4) known to have genetic susceptibility to Phytophthora root rot (PRR), sudden death syndrome (SDS), brown stem rot (BSR), white mold, or SCN will be. These plots will be co-located with and planted adjacent to the soybean foliar fungicide plots described in Objective I a. Diseases will be assessed visually and with laboratory analysis where needed. Insect populations will be rated and will be controlled if reaching economic threshold levels. Plots will be rated for insects and disease at approximately V3, R2-3 and R6 stages.

These plots are intended only to detect and provide an estimation of pest populations at each location and they may be destructively sampled for that purpose. Because soybean genetics will influence yield irrespective of pests and diseases, the sentinel varieties planted will be limited to one or two replications and yields will not be required.

Note: It has been difficult obtaining commercial soybean genetics with known susceptibility to multiple pathogens and susceptibility ratings are not standard across companies.

2. We recognize that soybean pests and diseases should be expected to appear in locations other than pre-planned sentinel plots. Accordingly, we propose to continue collate and validate reports of specific disease, nematode and insect problems that are submitted to University of Minnesota research and Extension personnel.

Of particular emphasis for collecting reports of distribution and damage during 2021 will be the soybean gall midge, Sudden Death Syndrome (SDS), frogeye leafspot, and Diaporthae/Phomopsis/SCN.

• If funded by this project, any submission of samples to the University of Minnesota Plant Disease Clinic (UMN PDC) and/or field observations by growers, ag industry or UMN campus or field faculty will be predicated on initial confirmation by photo. These additional data should improve the utility of sentinel plot information. Any such cooperative data collected will maintain grower confidentiality. Funding for overnight samples to the UMN PDC and limited mileage for visits to grower fields for follow-up are requested as part of this proposal.

Expected uses of these data include locations for field day discussions of soybean disease problems (virtual if COVID-19 hysteria persists), genetic or pesticide efficacy research, and soybean disease threshold (more appropriately viewed as disease yield - loss potential) research.

Expected deliverables (Objectives I, II)
Written results of experiments distributed through SW MN IPM Stuff and MN Crop News newsletters
Field and/or video tours of research sites
Availability for presentation of results at UMN and MN Soybean events
Objective III. Examine the distribution the host range and of the soybean gall midge in Minnesota. (Team: Bruce Potter and Dr. Bob Koch)

Justification: The soybean gall midge, Resseliella maxima (Gagne) is a new pest of soybeans in the Midwest; the species description published in 2019. What is believed to be the same species was reported from soybean in NE in 2011, and from SD, IA and NE in 2015 but at that time the insect was assumed to be as secondary invader of the soybean plant, following injury or plant disease. During June 2018, this insect was observed causing significant damage to soybean fields in these same states and determined to cause soybean damage by itself. SGM was confirmed as a pest of Minnesota soybeans in 2018 but according to one affected grower, it had been causing damage on his farm for at least three years. From 2018 to present, the soybean gall midge (SGM) has been confirmed in 5 states and 115 counties,16 of those counties in southwestern Minnesota (https://soybeangallmidge.org/soybean-gall-midge-distribution).

It is unknown if SGM is increasing in overall population density or distribution. This insect has been demonstrated capable of causing significant yield loss, up to 100 % on field edges. With a few notable exceptions to this point, infestations observed in Minnesota have been very localized within field edges. Based largely on a survey funded by the NCSRP, we have observed that within infested Minnesota counties, there are often foci where the insect can be found a high percentage of fields within in a local geography.

In addition to soybean, the soybean gall midge has been found on sweet clover and, to a lesser extent, alfalfa. It is possible that other legume crops (edible beans in particular) or native legumes are hosts.

Environmental and agronomic variables that influence SGM are not known. Tillage of soybean ground may affect overwintering larvae, spring pupation or adult emergence. During November 2020, a survey of Minnesota soybean growers was implemented to help understand regional differences in tillage and its possible relationship to SGM populations (z.umn.edu/SGM_survey).

This project will help track changes in distribution of soybean gall midge in Minnesota and begin to determine if additional Minnesota crops are at risk. It will complement the checkoff funding provided by the NCSRP.

Methods
a) Soybean gall midge hosts
Several soybean cultivars, several bean (Phaseolus vulgaris) cultivars (Navy, Pinto, kidney, black turtle), green bean mung bean, broad bean would be grown in containers in the greenhouse. On a weekly basis, these would be moved to SGM infested fields when the adults are active (data from NCSRP). Two weeks later each plant would be evaluated for infestation. If successful, this method would identify host preferences and determine risk to other crops in Minnesota relative to soybean. This work will compliment and be coordinated with proposed host studies at the University of Nebraska.

The SGM might be endemic, originally feeding on wild, native legumes. To examine this possibility, prairie clovers, partridge pea, native vetch spp. and etc., along with sweet clover along with sweet clover and introduced species will be sampled for the presence of SGM larvae during July and August. Wildlife areas and roadsides in SGM infested areas of SW and WC MN will be sampled. Larvae collected from alternate hosts will be submitted for a UNL study on SGM genetic diversity and will be available to be evaluated for parasitism.

b) Continued survey for changes in SGM distribution
During mid-August, counties bordering the western and eastern edges of known SGM distribution will be surveyed. Soybean field edges adjacent to corn where there is a grass or windbreak border will be preferentially selected. Three to five soybean fields/ county will be examined. Dense stands of sweet clover will also be examined. SGM larvae from this survey will be collected for genetic studies.

An electronic system for others to report photographic evidence of SGM and crop damage relates this objective with I b.

A soybean gall midge management publication and scouting and management videos will be updated and can be co-branded with MN SR&PC.

Proposed project timeline
April, May, June Plant host cultivars in greenhouse
June, July, August Move host plants to field during SGM adult flights
Evaluate plants for infestation
July, August Survey soybean and sweet clover in counties outside the known distribution of SGM
Survey native plants and sweet clover in geographies where SGM infestations occurred.
November Analyze results
December – March Present results
Release any videos developed
Expected deliverables:
New county observations will be reported via extension and ag media and data collated at the soybean gall midge.org website.
Research results of this objective will be distributed through UMN Extension newsletters.
New information will be used to update a SGM fact sheet and a SGM biology, soybean damage and scouting video.
Availability to present findings at UMN and MN soybean events