Project Details:

Determining soybean pest and pesticide interactions as a means to optimize soybean yield

Parent Project: Evaluation plant pest interactions to optimize soybean yield
Checkoff Organization:Iowa Soybean Association
Categories:Insects and pests, Crop management systems
Organization Project Code:
Project Year:2014
Lead Principal Investigator:Erin Hodgson (Iowa State University)
Co-Principal Investigators:
Aaron Gassmann (Iowa State University)
Gregory Tylka (Iowa State University)
Keywords: Best Management Practices, Soybean Aphid (SA), Soybean Cyst Nematode (SCN), Soybean Disease Management, Soybean Educational Activities

Contributing Organizations

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Information and Results

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Project Summary

The soybean cyst nematode (SCN) is widely considered to be one of the most damaging pathogens in most soybean-producing areas of the United States, including Iowa. Iowa soybean farmers have been battling SCN since it was discovered in 1978. The results of soybean-checkoff-funded surveys of Iowa in the mid-1990s and again in the last decade reveal that approximately 70-75% of Iowa fields are infested with the nematode. Yield losses of only 2-5 bushels per acre occur in growing seasons with adequate to excess moisture, but losses of 50% or more are common in very dry growing seasons.

Traditionally, SCN has been managed by growing a nonhost crop (typically corn) in rotation with SCN-resistant soybean varieties. This practice is effective at keeping population densities manageable, but it is not considered an effective remedy for a heavily-infested field.

Within the past two years, seed treatments have been made available to soybean farmers to provide early-season protection of developing roots from SCN and other plant-parasitic nematodes. University researchers are working to discern the conditions under which these seed treatments increase soybean yield and profitability. With the advent of new seed treatment management products and resistance of soybean varieties, there is a need to evaluate the interactions of these management tactics with soybean aphids and soybean cyst nematodes and to understand the effects of these management tactics on naturally occurring soil-borne organisms, which may play a critical role in keeping pest populations in check.

Project Objectives

1. Determine optimal yield potential using combinations of pest management tactics.
2. Evaluate interactions among host plant resistance, pesticides and pests to optimize yield.
3. Conduct greenhouse experiments to measure treatment effects on pest-killing pathogens and key soybean pests.
4. Promote optimal yield recommendations with multiple pest suppression tactics.

Project Deliverables

Optimal yield recommendations with multiple pest suppression tactics.

Progress of Work

Two field locations were established in 2013, including the Woodruff and Nashua Research Farms. Throughout the summer, extensive field work was carried out at both locations. The small plots at Woodruff were harvested on 3 October 2013 with the help of Chris Marett and Greg Gebhart (Tylka Nematology Lab). The small plots at Nashua were harvested on 10 October 2013 with the help of Stith Wiggs (Tylka Nematology Lab). The two middle rows for each plot were harvested and yield was calculated. The overall yield was higher at Nashua compared to the plots at Woodruff. The lower yields in the Woodruff experiment may be the result of several variables, including a late planting date, drought and higher initial population densities of SCN in the soil. At both locations, the two SBA-resistant soybean varieties (containing Rag1 genetics) yielded less than the two SBA-susceptible varieties. In a few instances, seed treatments provided small and insignificant yield increases.

On the same day of harvest, soil samples were collected from the plots in both experiments in order to determine the fall population densities of SCN. The reproduction factor for SCN (fall population densities divided by spring population densities) was estimated. This data can help explain which combination of soybean variety and seed treatment is most efficient for suppressing SCN reproduction. For all four soybean varieties planted at the Nashua location, the seed treatments ApronMaxx (fungicides) and Avicta Complete (combination of fungicides, insecticide, and nematicide) did not help reduce SCN reproduction compared to naked seed. The same trend held true for the SCN population densities at the Woodruff small plots. Regardless, the two soybean varieties with SCN resistance had less SCN reproduction than the two SCN susceptible varieties for both the Nashua and Woodruff plots. Seed treatments with a nematicide may not be a sufficient strategy for suppressing SCN.

Eric Clifton, Entomology Ph.D. student at Iowa State University, presented a poster on the results of the field study at the National Entomological Society of America (ESA) Meeting in November 2013. Eric also gave a ten-minute oral presentation on the first year of the field study at the ESA North Central Branch Meeting in March 2014. Eric is in the process of planning greenhouse and lab experiments that will complement the field research, including one that will test varieties of SCN-resistant soybeans that may confer resistance to aphids.

Final Project Results

The two field locations were scouted weekly for soybean aphid populations starting in late June and through mid-September when the populations decreased by more than 75% after one week. Cumulative aphid days (CAD) were generally lower this year compared to last year’s data. At the northeast location, aphid-susceptible plots had an average of 1172 ± 196 CAD; for the northwest location, only 188 ± 11 CAD. During the second week of October, both locations were harvested. Soil samples were taken on the days of harvest and will be processed for determining fall populations of soybean cyst nematode (SCN).

Harvest data for the northeast location was put into a mixed-model analysis of variance (ANOVA) and shows significant effects of seed treatment and its interactions with host plant resistance for soybean aphid or SCN. Pooling together all four varieties of soybeans, the plots with the Avicta Complete seed treatment yielded an average of 51.9 bushels/acre compared to the naked (no seed treatment) plots that yielded 44.1 bushels/acre. The same pattern holds true when we only look at the two nematode-susceptible beans. Again, the Avicta Complete treated beans yield significantly higher than the untreated beans. Once we have quantified SCN populations, we can determine whether or not the pest directly impacted yields and if the seed treatment helped to suppress the pest.

Eric Clifton will present data from both the 2013 and 2014 seasons of this project for a ten-minute competitive talk at the Entomological Society of America’s annual meeting that is being held Portland, Oregon on November 2014.

Benefit to Soybean Farmers

Performance Metrics

Project Years