By Liz Stahl, Extension Educator–Crops, Anthony Hanson, Extension Educator-Integrated Pest Management, and Dean Malvick, Extension Plant Pathologist
Soybean aphids, unconventional treatments, and crop diseases were the topic of conversation on the August 12th Strategic Farming: Field Notes program. Drs. Anthony Hanson, Extension Educator – Integrated Pest Management, and Dean Malvick , Extension Plant Pathologist, joined Ryan Miller, Extension Educator-Crops to discuss these issues and more.
Although the decision of whether or not to treat can get tougher as soybeans mature, if the economic threshold is reached just before R6 stage, one can treat for soybean aphid if populations reach threshold. The economic threshold (average of 250 aphids per plant, with 80% of the plants having aphids, and the population is increasing) is there to help protect yield and give enough time (5-7 days) to arrange an insecticide application before populations reach economically damaging levels around 670 aphids per plant. See Late-season soybean aphid scouting and management for a more detailed discussion that includes information on product selection. Pre-harvest intervals need to be taken into account as well as we get closer to the end of the growing season.
Sugar applications are not a recommended treatment for soybean aphid. Insects other than aphids are not as specialized in dealing with excess sugar in their diets, though applying sugar to crops isn’t likely to reduce their numbers either. One example is a study in Utah where sugar was applied to alfalfa plots to draw in parasitoid wasps that attack alfalfa weevil. Additional sugar resources generally can increase beneficial insect populations, but the follow-up question to ask is if that increase is enough to affect the pest population. While parasitoid numbers did increase in sugar-treated plots, alfalfa weevil numbers were not significantly changed either due to the increased parasitoid numbers or any potential direct effects of the weevils eating sugar on the plants.
Raising the Brix or internal sugar content of the plant itself is another idea brought up on the internet. The idea here is that population levels of insects drop when plants have a higher Brix content. The claims often state that the plants with higher Brix content are healthier and better able to fend off insects. Hanson reports he has not found data to support this when examining existing research and field trials looking for trends between Brix and insect populations. In some cases, research showed that plants with higher Brix contents actually had higher insect populations, while in other years or locations the opposite trend, or no trend, was seen. This generally indicates that if someone notices plants with higher sugar content and fewer insects, it’s more likely due to random chance rather than a cause-and-effect relationship. The bottom line is that even if something sounds convincing at first, check if independent field trials exist for any product being promoted to control insects, whether it’s a standard insecticide or another more creative solution like applying sugar or other chemicals.
On the disease front, hydrogen peroxide has been touted as an inexpensive method to help prevent white mold in soybean. NDSU compared applications of hydrogen peroxide to fungicide applications in 2023. While it appeared that the hydrogen peroxide treatments sometimes had slightly less white mold than the untreated check, no yield differences were found at the end of the season. A well-timed fungicide application, on the other hand, showed much potential to help protect yield.
While it is nearly impossible to test all the different alternative options people can think of, farmers and ag professionals are encouraged to check for University research data to see if research has been done to help back up claims. If there isn’t data to back up a claim by showing efficacy such as pest reductions or yield protection, that should be a red flag to growers trying to reduce crop input costs, even if the product being promoted is relatively inexpensive.
Sudden Death Syndrome (SDS) has been showing up in fields where rainfall has been adequate this year. There are no curative actions you can take when SDS is found now in a field, but there are steps you can take to help prevent issues in the future. These include using a seed treatment that is effective for control of SDS and selecting varieties with resistance to SDS. Note that the foliar symptoms of brown stem rot (BSR) can look very similar to SDS. One way to help tell the difference between these two diseases is to split the soybean stems. Plants with BSR will have a brown pith, while plants with SDS will not. However, a plant can have both BSR & SDS at the same time. There is also a BSR type that is widespread that only causes stem browning but not the foliar symptoms. Take a pocket knife with you to split stems when scouting fields. This will help you see if there is something going on in your soybean field that may not be readily apparent by foliar symptoms alone.
Check out Soybean Seed and Seedling Diseases for further details on specific diseases and identification resources.
Red Crown rot is another new soybean disease that is developing in the Midwest. It was found in one field in MN in the southwest corner last year. In IL, where it has been known to be for around the last 8 years, red crown rot has now been found across a big swath of the state. It has also been spreading more in IN.
The tops of plants with red crown rot can look very similar to SDS and brown stem rot. The difference is that there is usually a reddish discoloration at the base of plants with red crown rot. Sometimes, however, Rhizoctonia is what is really causing the discoloration.
Malvick encourages farmers and ag professionals to submit samples to the Malvick lab in the Department of Plant Pathology at the U of MN in St Paul this year if red crown rot is suspected in a field. Funding from the MN Soybean Research and Promotion Council is helping support sample analysis costs to help understand how widespread this disease is in the state. You can also first send Malvick (dmalvick@umn.edu) clear pictures of the top of the plant, the crown of the plant, and the roots, to help determine whether it is worth sending in a sample or not.
Regarding southern rust, there were big questions as we went into the 2026 season around how much of a problem this disease would be as it was a significant issue the past two years. Since this disease can only overwinter in subtropical areas where corn is grown year round – it needs a living corn plant to survive – what happens the previous year with southern rust in MN does not predict what will happen the following year. This disease has been developing in many areas of the state, but levels have been low. We are late enough in the season that there is a low risk of it developing to a level in most fields that could affect yield.
Tar spot, which does over winter in MN, has been reported across much of south-central MN, although levels have also been very low. It is encouraging that we are likely to get through this season as well without tar spot being a significant issue in many areas based on the low levels of disease found to date. Widespread hot and dry weather helped keep this disease at bay this year.
Thanks to the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council for their generous support of this program.
Soybean aphids, unconventional treatments, and crop diseases were the topic of conversation on the August 12th Strategic Farming: Field Notes program. Drs. Anthony Hanson, Extension Educator – Integrated Pest Management, and Dean Malvick , Extension Plant Pathologist, joined Ryan Miller, Extension Educator-Crops to discuss these issues and more.
Soybean aphid populations have been low
Hanson reported that although soybean aphid populations have generally been low to date, he has seen numbers increase in some fields. Aphid reproduction is slow when temperatures are in the 90s and nights are warm. Although recent cooler temperatures increase the potential for populations to increase quickly, we are getting near the end of August, so aphids should be moving to buckthorn soon. As the season continues to progress and soybeans reach the R6 stage (full seed), the economic threshold bumps up beyond 250, and insecticide applications are often not needed at this time as aphids also start to migrate back to buckthorn around late-August.Although the decision of whether or not to treat can get tougher as soybeans mature, if the economic threshold is reached just before R6 stage, one can treat for soybean aphid if populations reach threshold. The economic threshold (average of 250 aphids per plant, with 80% of the plants having aphids, and the population is increasing) is there to help protect yield and give enough time (5-7 days) to arrange an insecticide application before populations reach economically damaging levels around 670 aphids per plant. See Late-season soybean aphid scouting and management for a more detailed discussion that includes information on product selection. Pre-harvest intervals need to be taken into account as well as we get closer to the end of the growing season.
Creative/alternative solutions for pest control?
There have been a number of “creative solutions” one can find being promoted and discussed on the internet and on social media for control of pests. Some of these claims can sound very convincing or logical at first glance. One of these is applying sugar as an insecticide for soybean, alfalfa, and other field crops. One idea being stated about this strategy is the thought that aphids will get “diabetic” and die when exposed to sugar. Unfortunately, this claim does not match up with insect biology very well. Aphids actually can handle high sugar concentrations in plants. In order to get other nutrients from the plant while avoiding excess sugar, aphids feed by being able to shunt sugar away from their digestive tract and are highly specialized to secrete sugar as the honeydew that is often found on infested plants.Sugar applications are not a recommended treatment for soybean aphid. Insects other than aphids are not as specialized in dealing with excess sugar in their diets, though applying sugar to crops isn’t likely to reduce their numbers either. One example is a study in Utah where sugar was applied to alfalfa plots to draw in parasitoid wasps that attack alfalfa weevil. Additional sugar resources generally can increase beneficial insect populations, but the follow-up question to ask is if that increase is enough to affect the pest population. While parasitoid numbers did increase in sugar-treated plots, alfalfa weevil numbers were not significantly changed either due to the increased parasitoid numbers or any potential direct effects of the weevils eating sugar on the plants.
Raising the Brix or internal sugar content of the plant itself is another idea brought up on the internet. The idea here is that population levels of insects drop when plants have a higher Brix content. The claims often state that the plants with higher Brix content are healthier and better able to fend off insects. Hanson reports he has not found data to support this when examining existing research and field trials looking for trends between Brix and insect populations. In some cases, research showed that plants with higher Brix contents actually had higher insect populations, while in other years or locations the opposite trend, or no trend, was seen. This generally indicates that if someone notices plants with higher sugar content and fewer insects, it’s more likely due to random chance rather than a cause-and-effect relationship. The bottom line is that even if something sounds convincing at first, check if independent field trials exist for any product being promoted to control insects, whether it’s a standard insecticide or another more creative solution like applying sugar or other chemicals.
On the disease front, hydrogen peroxide has been touted as an inexpensive method to help prevent white mold in soybean. NDSU compared applications of hydrogen peroxide to fungicide applications in 2023. While it appeared that the hydrogen peroxide treatments sometimes had slightly less white mold than the untreated check, no yield differences were found at the end of the season. A well-timed fungicide application, on the other hand, showed much potential to help protect yield.
While it is nearly impossible to test all the different alternative options people can think of, farmers and ag professionals are encouraged to check for University research data to see if research has been done to help back up claims. If there isn’t data to back up a claim by showing efficacy such as pest reductions or yield protection, that should be a red flag to growers trying to reduce crop input costs, even if the product being promoted is relatively inexpensive.
Soybean disease update
Malvick reports that with most soybeans being at least in the R5 (beginning seed) stage, we are out of the optimal window to manage white mold with a fungicide this season. While symptoms typically start to show up now, the optimal time to apply a fungicide for white mold is R2 (full flower). Previously the recommendation was to apply at R1 (beginning flower), but research supports shifting this timing a little later to R2. This means we are well beyond a time in MN where a fungicide application could help for white mold in soybean. Keep records on where issues are seen this year so you can select varieties that are more resistant to white mold when soybeans are grown again in problem fields.Sudden Death Syndrome (SDS) has been showing up in fields where rainfall has been adequate this year. There are no curative actions you can take when SDS is found now in a field, but there are steps you can take to help prevent issues in the future. These include using a seed treatment that is effective for control of SDS and selecting varieties with resistance to SDS. Note that the foliar symptoms of brown stem rot (BSR) can look very similar to SDS. One way to help tell the difference between these two diseases is to split the soybean stems. Plants with BSR will have a brown pith, while plants with SDS will not. However, a plant can have both BSR & SDS at the same time. There is also a BSR type that is widespread that only causes stem browning but not the foliar symptoms. Take a pocket knife with you to split stems when scouting fields. This will help you see if there is something going on in your soybean field that may not be readily apparent by foliar symptoms alone.
Check out Soybean Seed and Seedling Diseases for further details on specific diseases and identification resources.
Red crown rot
.jpg "Red Crown Rot of soybean symptoms on leaves and stems") |
| Red crown rot of soybean symptoms include interveinal yellowing on soybean leaves, and reddish discoloration and fungal symptoms on the base of soybean plant stems. |
The tops of plants with red crown rot can look very similar to SDS and brown stem rot. The difference is that there is usually a reddish discoloration at the base of plants with red crown rot. Sometimes, however, Rhizoctonia is what is really causing the discoloration.
Malvick encourages farmers and ag professionals to submit samples to the Malvick lab in the Department of Plant Pathology at the U of MN in St Paul this year if red crown rot is suspected in a field. Funding from the MN Soybean Research and Promotion Council is helping support sample analysis costs to help understand how widespread this disease is in the state. You can also first send Malvick (dmalvick@umn.edu) clear pictures of the top of the plant, the crown of the plant, and the roots, to help determine whether it is worth sending in a sample or not.
Southern rust and tar spot update in corn
As the corn crop continues to mature, foliar diseases have been much less of a player this year compared to last year, and at this point in the season, foliar diseases have much less of a chance to cause an issue.Regarding southern rust, there were big questions as we went into the 2026 season around how much of a problem this disease would be as it was a significant issue the past two years. Since this disease can only overwinter in subtropical areas where corn is grown year round – it needs a living corn plant to survive – what happens the previous year with southern rust in MN does not predict what will happen the following year. This disease has been developing in many areas of the state, but levels have been low. We are late enough in the season that there is a low risk of it developing to a level in most fields that could affect yield.
Tar spot, which does over winter in MN, has been reported across much of south-central MN, although levels have also been very low. It is encouraging that we are likely to get through this season as well without tar spot being a significant issue in many areas based on the low levels of disease found to date. Widespread hot and dry weather helped keep this disease at bay this year.
Recordings available of all sessions
To listen to a recording of this session and other previous Strategic Farming: Field Notes sessions, visit z.umn.edu/strategic-farming. Stay tuned for Strategic Farming: Let’s Talk Crops to return this winter in January 2027!Thanks to the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council for their generous support of this program.
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