Angie Peltier, UMN Extension crops educator; Fei Yang, UMN Extension corn entomologist; Bruce Potter, UMN Extension IPM specialist; and Robert Koch, UMN Extension soybean entomologist
The following information was provided during the July 10, 2024 Strategic Farming: Field Notes session. Use your preferred podcasting platform or listen online to a podcast of this Field Notes session hosted by UMN Extension crops educator Claire LaCanne.
Mild winter
The following information was provided during the July 10, 2024 Strategic Farming: Field Notes session. Use your preferred podcasting platform or listen online to a podcast of this Field Notes session hosted by UMN Extension crops educator Claire LaCanne.
How a mild winter and a rainy spring impacts pests
 |
| Western corn rootworm |
The 2023-24 winter was a mild one in areas where agronomic crops are produced when compared to the average Minnesota winter. To help them survive cold winter temperatures, those insect pests that spend their winters in Minnesota tend to concentrate the fats and alcohols in their blood to produce a natural ‘antifreeze.’ However, the recent warmer than normal winter likely helped these pests’ (think alfalfa weevil, bean leaf beetle and European corn borer, etc.) survival.
Wet weather
Large weather systems that move from the south to the north in our continent bring more warm, humid air to Minnesota from further south. Along with precipitation, these weather systems bring north those pests that need warmer conditions to survive the winter. Pheromone traps used to monitor black cutworm and true armyworm moth migrations north had different results in 2024, with different consequences. Specifically, while significant captures of black cutworm occurred over a wide area, cutting injury to corn by black cutworm larvae was largely insignificant. It is theorized that as black cutworm moths prefer to lay their eggs in weedy field depressions, ponded water in these areas of fields may have impacted their survival. Except for traps in Roseau County, trap counts for true armyworm moths were very low. There have been reports throughout some areas of the state of armyworm injury in spring wheat fields - likely the result of too few traps being monitored over too large of an area to pick up local arrivals of significant populations.
Heavy rain can also affect the ability of very small insects to colonize crops. For example, rain storms occurring when soybean aphids were making their way from buckthorn to soybean may have decreased the survival of the aphids on the young soybean plants. Aphids have less protection from wind and rain on small plants. However in areas of southeast Minnesota, although overall soybean aphid population densities remain low, the percentage of plants infested in fields is quite high, nearing 100% in some fields. Soybean aphids have a very high reproductive capacity, capable of exponential growth under favorable conditions, making routine scouting a worthwhile endeavor in 2024. In addition, wet, humid weather can also favor the growth and development of fungi that can attack these pests and contribute to suppression of the pest populations. This is likely one reason why grasshopper populations have significantly declined after several dry growing seasons that were favoring population buildup.
There are two species of corn rootworm in Minnesota, western and northern corn rootworms. Western corn rootworm is infamous for being the costliest crop pest to manage due to costs associated with both yield losses and management. With repeated use of any management tactic, western corn rootworms have proved adept at overcoming management tactics. This is true for many of the insecticide chemistries that were used in broadcast applications, Bt biotech traits and even rotating to soybean (as observed in eastern corn-belt states). Greenhouse studies in Yang’s lab indicated a competitive advantage for western corn rootworm over northern corn rootworm. There is a worry that with a changing, warming climate and expansion of corn northward, western corn rootworm will march north and compete with northern corn rootworm as average temperatures rise.
Northern corn rootworm eggs are more cold tolerant than those of western corn rootworm. Select northern corn rootworm populations in Minnesota have just recently been confirmed to be resistant to both the Cry3Bb1 and the Cry 34/35Ab1 Bt traits. There are also Minnesota populations of northern corn rootworm that have evolved to overcome the corn-soybean rotation. Rootworm management still relies upon rotating to non-host crops and either rotating in-furrow insecticides or plant-incorporated protectants (Bt traits, RNAi). Work is continuing in the Yang lab to survey corn rootworm populations throughout the state for resistance.
New management techniques for rootworms may be on the horizon. Both Bayer Crop Science and Corteva have new Bt traits in their R&D pipeline and Dr. Yang’s lab is investigating an off-the-wall idea: absorbing carbon dioxide to manage rootworms. Corn rootworm larvae are attracted to respiring corn roots releasing carbon dioxide. The team is investigating applying in-furrow silicon rocks that absorb CO2. These rocks are being investigated for both plant health purposes and for rootworm management.
UMN Extension publishes models for seed corn maggot to show when risk at planting is high, particularly in fields with manure or green manure. There is unfortunately nothing that can be done for the crop after stand losses due to seed corn maggot, except to plan ahead to check the models before replanting this year or planting next year.
Heavy rain can also affect the ability of very small insects to colonize crops. For example, rain storms occurring when soybean aphids were making their way from buckthorn to soybean may have decreased the survival of the aphids on the young soybean plants. Aphids have less protection from wind and rain on small plants. However in areas of southeast Minnesota, although overall soybean aphid population densities remain low, the percentage of plants infested in fields is quite high, nearing 100% in some fields. Soybean aphids have a very high reproductive capacity, capable of exponential growth under favorable conditions, making routine scouting a worthwhile endeavor in 2024. In addition, wet, humid weather can also favor the growth and development of fungi that can attack these pests and contribute to suppression of the pest populations. This is likely one reason why grasshopper populations have significantly declined after several dry growing seasons that were favoring population buildup.
Corn rootworms – impacted by the wet spring?
Some insect pests that overwinter in the soil could be affected by saturated soils and flooded or ponded water. This is particularly true in fields flooded with warm, spring water, when a buildup of lactic acid can cause insect death in as few as 24 hours. Those with corn rootworms, particularly those with western corn rootworms that have proven to be so adept at evolving to resist our management strategies, were likely hoping that the extremely wet soil conditions and flooding would have had an impact on rootworm egg and larval survival. However, rootworm trials put out by Fei Yang’s lab have found very significant root pruning that will both affect overall yield potential and season-long standability, despite soils being very wet. One reminder – unless there is clipping of the silks to the extent that it would negatively impact fertilization (which is rare) by adult rootworm beetles, observations in 2024 should be used to inform 2025 rootworm management strategies.There are two species of corn rootworm in Minnesota, western and northern corn rootworms. Western corn rootworm is infamous for being the costliest crop pest to manage due to costs associated with both yield losses and management. With repeated use of any management tactic, western corn rootworms have proved adept at overcoming management tactics. This is true for many of the insecticide chemistries that were used in broadcast applications, Bt biotech traits and even rotating to soybean (as observed in eastern corn-belt states). Greenhouse studies in Yang’s lab indicated a competitive advantage for western corn rootworm over northern corn rootworm. There is a worry that with a changing, warming climate and expansion of corn northward, western corn rootworm will march north and compete with northern corn rootworm as average temperatures rise.
Northern corn rootworm eggs are more cold tolerant than those of western corn rootworm. Select northern corn rootworm populations in Minnesota have just recently been confirmed to be resistant to both the Cry3Bb1 and the Cry 34/35Ab1 Bt traits. There are also Minnesota populations of northern corn rootworm that have evolved to overcome the corn-soybean rotation. Rootworm management still relies upon rotating to non-host crops and either rotating in-furrow insecticides or plant-incorporated protectants (Bt traits, RNAi). Work is continuing in the Yang lab to survey corn rootworm populations throughout the state for resistance.
New management techniques for rootworms may be on the horizon. Both Bayer Crop Science and Corteva have new Bt traits in their R&D pipeline and Dr. Yang’s lab is investigating an off-the-wall idea: absorbing carbon dioxide to manage rootworms. Corn rootworm larvae are attracted to respiring corn roots releasing carbon dioxide. The team is investigating applying in-furrow silicon rocks that absorb CO2. These rocks are being investigated for both plant health purposes and for rootworm management.
Seed corn maggot in 2024
Years that are good for the seed corn maggot are years in which adult maggot (fly) flights coincide with corn or soybean planting. While many seed corn maggot infestations have been stopped in their tracks by seed treatment insecticides, the wet (saturated in many instances) field conditions in 2024 and inherent water solubility of the neonicotinoid seed treatments may have resulted in gaps in coverage during the period of most vulnerability for the crop - during the narrow window between egg laying and seedling emergence.UMN Extension publishes models for seed corn maggot to show when risk at planting is high, particularly in fields with manure or green manure. There is unfortunately nothing that can be done for the crop after stand losses due to seed corn maggot, except to plan ahead to check the models before replanting this year or planting next year.
Cover crops
A listener asked a question about using a cover crop to break up pest life cycles. While there has been research that has shown that planting soybeans green into a standing rye cover crop can reduce soybean aphid populations, a cover crop exacerbating pest and disease issues by creating a ‘green bridge’ between cash crops is more often the case. One of the primary means to manage pests is crop rotation. But for example if one rotates from a soybean crop in one year to a small grains cover crop to corn the following year, a population of true armyworms reaching the field is going to lay eggs in the nice thick stand of cover, only to move into corn (and even soybean!) when the cover is terminated. Care is required for pests that can cause stand or yield loss in our cash crops that are favored by cover crops.Questions about chlorpyrifos for pest management
Questions were raised about the use of chlorpyrifos for management of insect pests in 2024. The Minnesota Department of Agriculture was consulted after the discussion and an explanation of the current status is provided in an accompanying article. In response to the particular question about using chlorpyrifos-containing products in sunflowers, products with sunflowers on the label and still registered for use in Minnesota can be used for that crop. Check the MDA webpage or Kelly Solutions webpage for current listing of registered products for Minnesota.Additional Resources
- European corn borer - https://blog-crop-news.extension.umn.edu/2024/02/european-corn-borer-new-pest-old.html
- European corn borer in Minnesota field corn https://extension.umn.edu/corn-pest-management/european-corn-borer-minnesota-field-corn
- Scouting for corn rootworm https://extension.umn.edu/corn-pest-management/scouting-corn-rootworm
- Handy Bt Trait table (pdf) https://www.texasinsects.org/uploads/4/9/3/0/49304017/24_bttraittable_march2024.pdf
- Handy Bt Trait Table: https://www.texasinsects.org/bt-corn-trait-table.html
- Products registered for ag use in MN: https://www2.mda.state.mn.us/webapp/lis/productsdefault.jsp
- Insecticide-resistance management: https://iwilltakeaction.com/insects/
- CHLORPYRIFOS INSECTICIDE - MDA https://www.mda.state.mn.us/pesticide-fertilizer/chlorpyrifos-insecticide#:~:text=The%20MDA%20cancelled%20chlorpyrifos%20product,on%20raw%20agricultural%20commodities%20and
- Final Cancellation Order for Cancelling Certain Pesticide Registrations and Uses https://www.federalregister.gov/documents/2024/06/24/2024-13779/final-cancellation-order-for-cancelling-certain-pesticide-registrations-and-uses
Comments
Post a Comment