2015
Management and outreach for soybean insect and mite pests in South Dakota
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Contributor/Checkoff:
South Dakota Soybean Research and Promotion Council
Category:
Sustainable Production
Keywords:
Biotic stressCrop protectionField management Pest
Parent Project:
Management of soybean insect and mite pests in South Dakota
Lead Principal Investigator:
Kelley Tilmon, South Dakota State University
Co-Principal Investigators:
Project Code:
Contributing Organization (Checkoff):
South Dakota Soybean Research and Promotion Council
(n/a)
Institution Funded:
South Dakota State University
(n/a)
Brief Project Summary:

Yield loss from insects and the costs to manage them are important in the bottom line of soybean production. This project encompasses a range of management-related objectives including experiments to assess the efficacy of seed treatments, foliar insecticides and miticides, and aphid-resistant varieties; on-farm surveys and monitoring for pest outbreaks; exploration for new aphid resistance genes; and the publication of outreach material to inform producers about soybean insects and management. The goal of this work is to increase the profitability and sustainability of insect pest management for South Dakota soybean producers by providing research-based information on pest control strategies.

Key Benefactors:
farmers, agronomists, extension specialists, ag retailers

Information And Results
Final Project Results

1) Examine the efficacy of neonicotinoid seed treatments and foliar sprays for soybean pest management
This was a Tilmon/Szczepaniec joint experiment planted at the SDSU research farms in Volga
and South Shore. The study examined the effect of neonicotinoid seed treatment
(thiamethoxam) and neonicotinoid foliar application (imidacloprid) on arthropods (aphids and
spider mites). This was the final year in a multi-year study on the economic return on
insecticidal seed treatments in soybean, and also provided data on the impact of neonicotinoids
on spider mite abundance. Other studies suggest that neonicotinoids may actually increase
spider mite populations.

Key Findings (Economic Analysis)
•In a cost/benefit analysis of thiamethoxam seed treatment (the active ingredient in
Cruiser) compared to IPM (scouting, with a foliar application at threshold), the
probability of net return and the average net returns when they existed were:
o Seed treatment: 66.2% chance of a return, @ $6.02/acre
o IPM: 94.5% chance of a return, @ $21.02/acre

•In many instances in this multi-year, multi-state study, seed-treated plots would have
required scouting and a foliar application to protect yield (if they were in commercial
fields), further increasing cost with no added benefit compared to IPM alone.

•Conclusion: Thiamethoxam seed treatment is less likely to provide an economic return,
and the possible returns are much lower, than with scouting/foliar management.

Key Findings (Spider Mites)
•Neonicotinoids in general (looking at seed treatment and foliar treatments together),
significantly increased spider mite abundance.

•This effect was more pronounced with the foliar neonicotinoid. But when considered separately (i.e., not combining effects from seed and foliar treatments), differences were not significant. •?This effect was more pronounced with the foliar neonicotinoid. But when considered separately (i.e., not combining effects from seed and foliar treatments), differences were not significant.

Conclusions: Neonicotinoid seed treatments alone may not increase spider mite
populations significantly, however the higher doses found in foliar application are likely
to trigger spider mite increases.
•However, under hot and dry conditions that favor spider mites, there is the potential for
an interaction with seed treatments that could increase the likelihood of spider mite
outbreak. Further research is needed to examine this idea.
•Results are being prepared for submission to a scientific journal.

2) Resistant variety efficacy trial for advanced breeding lines
The purpose of this study was to evaluate experimental triple-gene stacks (Rag1 + Rag2 + Rag3)
of aphid resistance genes for soybean aphid suppression. However, we were not able to obtain
sufficient quantity of breeder’s seed for a trial, and this objective was deferred to a future date
when sufficient seed is available. However, we disseminated preliminary information from
earlier seasons of this project (looking at two-gene pyramids) in extension presentations in the
winter of 2014/2015.

3) Screen aphid field genotypes for tolerance to aphid-resistant varieties
The purpose of this study was to conduct the first season in a multi-year study to screen South
Dakota aphid populations for the presence of resistance-breaking biotypes. These biotypes
could potentially shorten the useful lifespan of aphid-resistant varieties. This objective was
originally planned as a greenhouse bioassay with most of the work to be performed in the fall.
However, due to an extended illness the PI (Tilmon) was unable to complete the work as
proposed. Instead, this objective was reduced to a preliminary field screening study, with more
detailed bioassay work to be performed in FY16 with additional leveraged funding from USB.

Preliminary Findings
•2014 field screening showed a low but relevant number of aphid colonists able to
survive on plants with the Rag1 resistance gene.
•This suggests that the potential exists for Rag1 resistance-breaking populations to
develop in South Dakota, though the timeline and severity of the appearance of such
populations can’t be determined yet.

4) Updated soybean aphid factsheet
The purpose of this objective was to update the SDSU soybean aphid extension factsheet with
the most current information on soybean aphid biology and management.

•This objective was completed as planned, with the factsheet content submitted to
iGrow for layout and printing.

•This factsheet will be available as a free download from iGrow or in hard copy, with the
support of the South Dakota Soybean Research and Promotion Council acknowledged.

Tilmon/Hesler Objective
1) Identify new aphid-resistant sources in MG I & II soybeans
The purpose of this objective was to screen germplasm for new sources of resistance to
soybean aphid. Because of the potential for resistance-breaking aphid biotypes to arise, it is
important to find new resistance genes for future breeding efforts to develop new aphidresistant cultivars. Screening efforts were focused on maturity groups I and II.

Key Findings
•During the reporting period, 390 lines were screened for aphid resistance.
•Overall, 11 lines showed resistance to biotype 1 (“normal”) soybean aphids.
•These lines have been advanced for additional testing to determine how they hold up
against different aphid biotypes.
•In addition, five aphid-resistant lines of wild soybean lines that were identified in the
previous year have been advanced for further testing.
•This project supported a Master’s student who graduated this year.
•This project also supported an undergraduate Honors research project with the student
going on to enroll in a Master’s program at SDSU.

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.