Liz Stahl, Extension Educator- Crops, and Anthony Hanson, Extension Educator - IPM, and Bob Koch, Extension soybean entomologist
Each year, farmers provide feedback at Private Pesticide Applicator Recertification workshops regarding their practices and challenges faced when managing crop production pests. Besides providing an opportunity for attendees to see what others are doing in an anonymous way, this information provides guidance in identifying research and educational needs around integrated pest management (IPM). In 2022, this feedback was collected using Echo360 (formerly TurningPoint) clickers. Note, all responses are voluntary and completely anonymous, and information is pooled across respondents at a particular site.
The following are some highlights from the 2022 survey that may provide some insight when making pest management decisions this growing season.
This compares to research conducted by the U of MN where samples from 90 waterhemp populations were collected in the fall and screened for herbicide resistance from 2021-2023 (Singh, N., et al., 2023). In this research, 89% of the populations were found to be moderately to highly resistant to glyphosate, and 100% were found to be moderately to highly resistant to Raptor (Group 2 herbicide). Although this research was conducted on populations suspected to be herbicide-resistant, these results indicate that the actual extent of herbicide-resistance is likely more wide-spread than farmers may realize.
It is important to note that 19% of respondents indicated they thought they had weeds with resistance to glufosinate, although there are no officially known or confirmed cases of resistance to this herbicide in MN to date. Application techniques (e.g. nozzle selection, gallonage, coverage, adjuvants), weed height at the time of application, and environmental conditions at the time of application can all significantly impact the efficacy of glufosinate, and other herbicides as well. These factors may have played a role in reduced efficacy, highlighting the importance of checking the herbicide label for any restrictions or guidance to optimize control.
Most of the farmers reported using non-chemical weed control strategies: Only 14% of respondents reported that they did not use them (Question 2). Rotating herbicide-resistant traits was the most commonly selected (50% of respondents), while altering the planned crop rotation, hand-pulling weeds/rouging and using mechanical weed control were the next most commonly selected tactics, at 37, 37, and 23% of respondents, respectively.
The following tables contain select results from the 2022 U of MN Extension IPM Assessment.
Question 1. Do you think you have weed resistance to any of the following on the land you farm? (select all that apply)* (Respondents = 887)
Question 2. In 2021, I used the following non-chemical weed management practices on the land that I farm (select all that apply)* (Respondents = 823)
Koch, R., Potter, B., Glogoza, P., Hodgson, E., Krupke, C., Tooker, J., DiFonzo, C., Michel, A., Tilmon, K., Prochaska, T., Knodel, J., Wright, R., Hunt, T., Varenhorst, A., McCornack, B., Estes, K., and Spencer, J. (2016). Biology and Economics of Recommendations for Insecticide-Based Management of Soybean Aphid. Plant Health Progress, 17:265-269. https://apsjournals.apsnet.org/doi/epdf/10.1094/PHP-RV-16-0061
Singh, N., Sarangi, D., Miller, R., Peters, T. and Naeve, S. (2023). Multiple herbicide-resistant waterhemp is spreading rapidly across Minnesota. MN Crop News, https://blog-crop-news.extension.umn.edu/2023/06/multiple-herbicide-resistant-waterhemp.html.
The following are some highlights from the 2022 survey that may provide some insight when making pest management decisions this growing season.
Weed management
Most farmers report dealing with herbicide-resistant weeds: Only 15% of respondents reported that they didn’t think they had herbicide-resistant weeds on the land they farmed (Question 1). Resistance to glyphosate was by far the most common (67%), while only 15% thought they had resistance to the ALS-inhibitors (Group 2 herbicides such as Pursuit and FirstRate).This compares to research conducted by the U of MN where samples from 90 waterhemp populations were collected in the fall and screened for herbicide resistance from 2021-2023 (Singh, N., et al., 2023). In this research, 89% of the populations were found to be moderately to highly resistant to glyphosate, and 100% were found to be moderately to highly resistant to Raptor (Group 2 herbicide). Although this research was conducted on populations suspected to be herbicide-resistant, these results indicate that the actual extent of herbicide-resistance is likely more wide-spread than farmers may realize.
It is important to note that 19% of respondents indicated they thought they had weeds with resistance to glufosinate, although there are no officially known or confirmed cases of resistance to this herbicide in MN to date. Application techniques (e.g. nozzle selection, gallonage, coverage, adjuvants), weed height at the time of application, and environmental conditions at the time of application can all significantly impact the efficacy of glufosinate, and other herbicides as well. These factors may have played a role in reduced efficacy, highlighting the importance of checking the herbicide label for any restrictions or guidance to optimize control.
Most of the farmers reported using non-chemical weed control strategies: Only 14% of respondents reported that they did not use them (Question 2). Rotating herbicide-resistant traits was the most commonly selected (50% of respondents), while altering the planned crop rotation, hand-pulling weeds/rouging and using mechanical weed control were the next most commonly selected tactics, at 37, 37, and 23% of respondents, respectively.
The following tables contain select results from the 2022 U of MN Extension IPM Assessment.
Question 1. Do you think you have weed resistance to any of the following on the land you farm? (select all that apply)* (Respondents = 887)
| Herbicide | Percent respondents |
|---|---|
| Glyphosate (e.g. Roundup) | 67 |
| Glufosinate (e.g. Liberty) | 19 |
| PPO-inhibitors (e.g. Flexstar, Cobra) | 17 |
| ALS-inhibitors (e.g. Pursuit, FirstRate) | 16 |
| No, I don't think so | 15 |
| HPPD-inhibitors (e.g. Callisto, Laudis) | 6 |
| Atrazine | 4 |
| Other | 4 |
*Could select as many answers as applied
Source: L.Stahl, A Hanson, R Miller, D. Nicolai, and A Peltier, 2022
Question 2. In 2021, I used the following non-chemical weed management practices on the land that I farm (select all that apply)* (Respondents = 823)
| Non-chemical practice | Percent respondents |
|---|---|
| Rotated herbicide-resistant traits (e.g. Liberty/dicamba/2,4-D) | 50 |
| Altered planned crop rotation | 37 |
| Hand-pulled weeds/rouging | 37 |
| Mechanical weed control (e.g. cultivation, rotary hoe) | 23 |
| Planted cover crops | 14 |
| Did not use non-chemical weed management | 14 |
| Delayed planting/tillage/stale seedbed | 10 |
| Harvested weedy areas separately | 8 |
| Other | 2 |
*Could select as many answers as applied
Source: L.Stahl, A Hanson, R Miller, D. Nicolai, and A Peltier, 2022
Soybean Aphid Management
Forty-five percent of respondents indicated that they used the economic threshold of 250 aphids/plant when deciding when to spray for soybean aphid (Question 3). Thirty-two percent of respondents, however, indicated that they believed the 250 aphids/plant threshold was too high (they spray earlier).These results indicate there is still skepticism about the threshold even though University research has continued to support the ET of 250 aphids/plant for over a decade. It's key to note that the ET gives some lead time before aphids could reach an economically damaging population of about 670 aphids/plant and applications before the ET of 250 aphids/plant are unlikely to result in an observable yield protection or return on investment. Furthermore, such applications can 1) kill off beneficial insects that are helping keep soybean aphid populations in check and 2) select for more insecticide resistance in soybean aphid populations. With the documented resistance of soybean aphid to pyrethroids (e.g. lambda-cyhalothrin, bifenthrin) in MN that has led to control failures, along with the recent loss of chlorpyrifos as a tool for soybean aphid management, preservation of effective insecticides for control of soybean aphid is as important as ever.
Question 3. How do you decide when to spray for soybean aphids?* ** (select all that apply) (Respondents = 689)
| Treatment time | Percent respondents |
|---|---|
| I use the Economic Threshold (ET) and apply after the 250 aphids/plant threshold | 45 |
| I spray when my agronomist/crop consultant/co-op tells me to | 34 |
| I believe the 250 aphids/plant threshold is too high (I spray earlier) | 32 |
| I do not spray insecticide for soybean aphid control | 9 |
| I spray aphids as a tank mix with a herbicide or fungicide, targeted for weeds or disease | 7 |
| I spray once the soybeans reach a particular growth stage or around a particular calendar dat | 3 |
| I spray when custom applicators are in the area | 3 |
| I don't scout, I spray when my neighbors do | 2 |
*Could select as many answers as applied
**For those that planted corn and/or soybean
Source: L.Stahl, A Hanson, R Miller, D. Nicolai, and A Peltier, 2022
Foliar Fungicide Use
Over the past few years, farmers have been asked if they used a foliar fungicide in corn (Question 4) or soybean (Question 5), and if they did, what kind of a yield response did they see. Of the respondents that planted corn in 2021, 76% did not use a fungicide in corn. Of those who did apply a fungicide in corn, 8% reported measuring a yield response greater than or equal to 6 bu/ac, 6% reported measuring a yield response up to 5 bu/a, while 10% reported they did not see a positive yield response.Of the respondents that planted soybean in 2021, 70% did not use a fungicide in soybean. Of those that did apply a fungicide in soybean, 9% reported measuring a yield response greater than or equal to 4 bu/ac, 11% reported measuring a yield response up to 3 bu/a, while 10% reported they did not see a positive yield response.
Corn and soybean foliar disease levels in MN are typically not at a high enough level where a foliar fungicide application will pay off. This is not always the case, however, highlighting the importance of scouting for any issues throughout the season.
Question 4. Did you apply a foliar fungicide in corn in 2021?** (Respondents - 760)
Question 5. Did you apply a foliar fungicide in soybean in 2021?** (Respondents = 754)
Corn and soybean foliar disease levels in MN are typically not at a high enough level where a foliar fungicide application will pay off. This is not always the case, however, highlighting the importance of scouting for any issues throughout the season.
Question 4. Did you apply a foliar fungicide in corn in 2021?** (Respondents - 760)
| Fungicide use | Percent respondents |
|---|---|
| No, I did not apply a foliar funcidie in corn | 76 |
| Yes, but I did not see a positive yield response | 10 |
| Yes, and I measured a yield response ≤6 bu/acre | 8 |
| Yes, and I measured a yield response up to 5 bu/acre | 6 |
**For those that planted corn and/or soybean
Source: L.Stahl, A Hanson, R Miller, D. Nicolai, and A Peltier, 2022
Question 5. Did you apply a foliar fungicide in soybean in 2021?** (Respondents = 754)
| Fungicide use | Percent respondents |
|---|---|
| No, I did not apply a foliar fungicide in soybean | 70 |
| Yes, and I measured a yield response up to 3 bu/acre | 11 |
| Yes, but I did not see a positive yield response | 10 |
| Yes, and I measured a yield response ≤4 bu/acre | 9 |
**For those that planted corn and/or soybean
Source: L.Stahl, A Hanson, R Miller, D. Nicolai, and A Peltier, 2022
Follow IPM guidelines when managing pests
Following IPM guidelines when making pest management decisions can help preserve the long-term effectiveness of pesticides, reduce the potential for any negative environmental impacts from using pesticides, and help a farmer’s bottom line. These tips are adapted from a list of insecticide resistance management strategies:- Scout for issues and properly identify the pest you are dealing with. Proper identification is key in knowing how to best manage a pest, including when a pest would be most susceptible to a control tactic, (including a pesticide), and when it is not.
- Use multiple strategies, including non-chemical strategies, for pest management including genetic (e.g. pest-resistant varieties), biological, mechanical control tactics, and cultural control (e.g., crop rotation).
- Base applications on economic thresholds when available (e.g. soybean aphid) and applicable. Use U of MN Extension resources to help with management decisions:
- Soybean Pest Management (for diseases and insects)
- Corn Pest Management (for diseases and insects)
- Small Grains Pest Management (for diseases and insects)
- Weed management, including Weed identification and Herbicide-resistance management
- Apply pesticides the right way (e.g. appropriate nozzles, gallonage, rate), at the right time (e.g. appropriate pest stage), and according to label directions.
- When using pesticides, diversify modes and sites of action. For example, don't use the same insecticide or fungicide mode of action in a season if more than one application is needed in a year. For herbicides, use multiple sites of action in an application and diversify sites of action across years.
Sources
Koch, R., MacRae, I., and Potter, B. (2022). Insecticide resistance management in soybean. https://extension.umn.edu/soybean-pest-management/insecticide-resistance-management-soybeanKoch, R., Potter, B., Glogoza, P., Hodgson, E., Krupke, C., Tooker, J., DiFonzo, C., Michel, A., Tilmon, K., Prochaska, T., Knodel, J., Wright, R., Hunt, T., Varenhorst, A., McCornack, B., Estes, K., and Spencer, J. (2016). Biology and Economics of Recommendations for Insecticide-Based Management of Soybean Aphid. Plant Health Progress, 17:265-269. https://apsjournals.apsnet.org/doi/epdf/10.1094/PHP-RV-16-0061
Singh, N., Sarangi, D., Miller, R., Peters, T. and Naeve, S. (2023). Multiple herbicide-resistant waterhemp is spreading rapidly across Minnesota. MN Crop News, https://blog-crop-news.extension.umn.edu/2023/06/multiple-herbicide-resistant-waterhemp.html.
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