Herbicide resistant volunteer corn control in soybean continues to be a challenge for farmers in Minnesota. Volunteer corn (VC) can directly impact soybean production by competing with soybean and reducing yield, VC can create harvest challenges, and lead to issues with foreign material in harvested soybean grain. In addition, VC in soybeans can have implications for effective corn rootworm management, and corn rootworm is one of the biggest threats to corn production which impacts many soybean growers.
Further complicating the management of VC is the adoption of Growth Regulator Tolerant (GR) soybeans. It has been well documented that herbicide tank mixes with growth regulators (e.g. Enlist and Xtend) and graminicides (e.g. Select Max and Assure II) can reduce grass and VC control in soybean. In a 2021 winter survey of 649 Minnesota soybean growers 52% indicated they would plant E3 enlist soybeans, 19% would plant XtendFlex soybeans, and 32% would plant Xtend soybeans. The survey question was about soybean herbicide resistance trait selection for 2022 planting intentions, so growers may have selected more than one technology, but what remains clear is that there has been widescale adoption of these growth regulator technologies.
These challenges in controlling VC in GR tolerant soybeans have been realized by many soybean growers. Conversations with farmers and retail agronomists this past summer has led me to believe we have more questions than answers on how to best control volunteer corn. This project will help determine the best and most cost-effective approaches to managing VC.

1. Determine the best and most cost-effective herbicide program for weed and volunteer corn control in growth regulator tolerant soybeans.
2. Evaluate the potential for herbicide antagonism between the growth regulators and graminicide (i.e. controls grasses and volunteer corn) herbicides.
3. Demonstrate a layered residual herbicide and evaluate any impact it has on volunteer corn control.
4. Communicate these results with Minnesota farmers and Ag professionals working with these farmers.

1. At each site, the project will be incorporated into public field days for farmers and ag professionals. This project will also be highlighted during small group tours that are available to be scheduled upon request of small groups of farmers, retailers, or industry representatives.
2. In-season updates will be provided via extension crop news blog, twitter posts, and on the strategic farming webinar series.
3. At season’s end the results will be summarized and published in a research report, to be posted on the web.
4. Results will be disseminated via traditional extension activities including winter meetings, workshops, webinars, and newsletters/blogs.
5. We will post a short video on the crops YouTube channel.
6. We will cover this project/subject on the Gopher Coffee Shop Podcast
7. Results will be incorporated into a “Best Practices” segment on the Farm Connections television program. The Farm Connections program airs on KSMQ out of Austin, MN and Pioneer TV out of Granite Falls, MN.
8. We will explore opportunities to collaborate with some of the Northern Soybean Marketing efforts on foreign material in soybean grain and export implications.

An eighteen-treatment randomized complete block design experiment will be conducted at Rochester, MN and the Research and Outreach Center in either Waseca or Rosemount, MN. Fields will be prepared, and herbicide tolerant volunteer corn will be incorporated/planted, then soybeans will be planted in 30-inch rows. A preemergence herbicide will be sprayed at the time of planting and will be followed by an appropriately timed postemergence application to control weeds including the volunteer corn. Weed and volunteer corn control will be visually rated at 7, 14, and 21 days after POST application treatment, and a late season visual assessment will be conducted prior to harvesting plots. Plots will be harvested for grain yield calculations. A phone and email survey will be conducted to determine the costs of various herbicide programs.
Proposed Treatments:
PREEMERGENCE
All treatments will start with a preemergence (e.g. Broadaxe XC) at planting.
POSTEMERGENCE
1. Enlist + Glyphosate + Select Max 6 oz + (AMS & NIS)
2. Enlist + Glyphosate + Select Max 6 oz + Dual + (AMS & NIS)
3. Enlist + Glyphosate + Select Max 9 oz + (AMS & NIS)
4. Enlist + Glyphosate + Select Max 9 oz + Dual + (AMS & NIS)
5. Enlist + Select Max 6 oz + (AMS & COC)
6. Enlist + Select Max 6 oz + Dual + (AMS & COC)
7. Enlist + Select Max 9 oz + (AMS & COC)
8. Enlist + Select Max 9 oz + Dual + (AMS & COC)
9. Enlist + Glyphosate + Assure II 4 oz + (AMS & NIS)
10. Enlist + Glyphosate + Assure II 4 oz + Dual + (AMS & NIS)
11. Enlist + Glyphosate + Assure II 5 oz + (AMS & NIS)
12. Enlist + Glyphosate + Assure II 5 oz + Dual + (AMS & NIS)
13. Enlist + Assure II 4 oz + (AMS & COC)
14. Enlist + Assure II 4 oz + Dual + (AMS & COC)
15. Enlist + Assure II 5 oz + (AMS & COC)
16. Enlist + Assure II 5 oz + Dual + (AMS & COC)
17. Enlist + Glyphosate+ (AMS) fb1 Select Max 6 oz + (COC & AMS)
18. Enlist + Glyphosate + (AMS) fb Assure II 4 oz + (COC & AMS)
1= graminicide in a sequential treatment 5-7 days after initial POST treatment

Update:
8-29-2022 Research Progress Report:
Managing Volunteer Corn in Growth Regulator Tolerant Soybeans
Trials were conducted in Waseca, MN at the Southern Research and Outreach Center and at the University of MN Weed Management site in Rochester, MN. Based on consultation with crop protection representatives we made slight adjustments to the graminicide rates in the proposed treatment list. Plots were planted, sprayed, rated, and photos were taken. Plots at both sites are awaiting harvest. A final data summary will be included in the November progress report.

Update:
The field projects have been completed and the results have been summarize. We are in the process of creating outreach materials and will be sharing those in various methods in the coming months. So far, results have been presented at one farmer field day in Freeborn County (30 farmers). More events are planned in the coming weeks.

View uploaded report

Update:
Slide and poster presentations were developed, and results have been shared at several farmer meetings and conferences this winter. These include the MN Crop Pest Management Short course, Prairie Grains, MN Ag Expo in Mankato, the Southern Research and Outreach Center Winter Crops Days, and the North Central Weed Science Society annual meeting. It was also used in training materials for commercial and private pesticide applicator recertification workshops. To date it was used at 8 commercial workshops and at least 19 private/farmer applicator workshops.

View uploaded report

Update:
A summary of methods and results is attached to progress of work 2. For this progress report I will focus the summary of outreach activities:
4 Field day presentations (approximately 200 farmers and ag professionals)
3 Winter weed management presentations for farmers (approximately 100 farmers)
19 Private applicator workshops (Over 600 farmers)
10 Commercial applicator workshops (900-1,000 applicators working for farmers)
1 Poster North Central Weed Science Society Annual Meeting
1 Poster MN Ag Expo

Farmers using 2,4-D tolerant soybeans need to adjust their spray plans to adequately control volunteer corn. 2,4-D is the main factor causing antagonism and reduced volunteer corn control in the tank-mixes we tested. If grass controlling herbicides (graminicides) are tank mixed with 2,4-D, the farmer must use increased rates of graminicides to overcome herbicide antagonism and insufficient volunteer corn control. A second strategy is to use sequential applications with grass controlling herbicides applied 7 days after application of 2,4-D and glyphosate. With sequential applications we were able to maintain adequate volunteer corn control with lower rates of grass controlling herbicides. A second year of this study has been funded by Minnesota Soybean and the studies have been established at Waseca and Rochester. Once the results have been confirmed we will create a full report with guidelines for growers.

The research project will help find the best and most cost-effective herbicide programs for controlling volunteer corn in an GR tolerant soybean herbicide program. The project is also designed to identify herbicide program options for VC management. Options are important, in recent years herbicide supply shortages have made it imperative that growers have multiple options for when their first choice is not available or becomes unavailable. In addition, we have designed the project to help address future VC control issues that are likely to arise. Enlist corn with FOP herbicide (e.g. Assure II) tolerance, is likely to enter the Minnesota marketplace in the near future, and we have included the Select Max herbicide option for controlling FOP tolerant volunteer corn. The outreach plan highlighted in the deliverable’s sections will reach many growers and ag professionals.