April showers bring May flowers and the frequent use of windshield wipers.
After the first spring shower, flipping the wipers on was a bit refreshing for me. With a dry fall and spring for many Missouri soybean farmers, rainfall was a pleasant site and necessary to replenish water levels in irrigation and fishing ponds and subsoils.
Periods of excessive rainfall — or lack of it — coupled with extreme temperature swings seem to be more common in recent years when planting is underway. Determining how long the weather fluctuation will last can create undue stress. Combine that stress with high input costs and increased lending rates, and sound judgment may be compromised when deciding to plant or not.
While the weather is something we can’t control, using a soybean fungicide and insecticide seed treatment or an inoculant are decisions we can. These products can provide comfort by protecting the germinating seed from a hostile environment and certain seed-attacking predators.
There are many factors and questions that need to be addressed before selecting the proper seed treatment for your soybean crop:
1) How long has it been since the field was planted with soybeans and inoculated with Bradyrhizobium japonicum (B. japonicum)?
Bradyrhizobium japonicum converts atmospheric nitrogen gas to ammonia, which then undergoes additional chemical reactions to make plant-available forms of nitrogen, ammonium and nitrate. The symbiotic relationship between soybean and B. japonicum is critical when it comes to producing a high-yielding crop. An adequate number of B. japonicum will be necessary for this process to run efficiently.
Fields previously in long-term CRP, pasture or hay may not have the quantity of B. japonicum in the soil to supply the high nitrogen demand necessary for grain fill. Therefore, in these situations, nitrogen would need to be extracted from soil to meet seed nitrogen demand. When growing soybeans, nitrogen is one nutrient that can be overlooked, assuming the crop will generate its own. Soybeans can store four times or more nitrogen in a bushel of grain when compared to the amount of nitrogen removed from soil and stored in corn grain.
Soils with a pH below 5.5 or above 8 will negatively impact B. rhizobium survival1. In a multistate study, a greater response to B. japonicum inoculation was observed in June-planted soybean when compared to April-planted soybean. The study emphasized the importance of inoculating later soybean crops, which on average produced 8% more bushels than non-inoculated late-planted soybean2.
The bottom line is we haul a lot of nitrogen and other nutrients out of the field in the fall with every load of soybean, and much of that nitrogen can be supplied without mining it from the soil. Practicing crop rotation and soil sampling are easy starting points to maintain B. japonicum numbers.
2) Have you been growing soybean more than two years in a row and has there been a history of disease pressure?
Diseases are often diagnosed after serious infection occurs. Injury symptoms or unusual plant growth draws attention to the consultant or producer and frequently triggers a further investigation. In Missouri, Fusarium spp., pythium, phytophthora and Rhizoctonia are the more common early-season pathogenic fungi that survive in soil and/or crop residue and cause issues for producers. These fungi can be found wherever soybean is grown and under continuous monoculture production systems where inoculum levels in the soil can build. For example, if left unmanaged, nearly 50% soybean stand reduction from Rhizoctonia infection can occur3. Fortunately, many commercially available seed treatments that offer multiple modes of action can combat several of these diseases.
3) Are you planting early?
The desire to plant soybean early has been a topic of discussion with many producers. An adequate soybean stand may be compromised when planted in less-than-ideal field conditions. Soybean fungicide seed treatments can help in mitigating some of the negatives that inherently come with a decision to plant early.
Soybean seed planted in moist, cool soil with temperatures below 60 degrees Fahrenheit resulted in a positive net return at 12 out of 14 locations when a two-modes-of-action fungicide seed treatment was applied versus no seed treatment4. Fields planted early and exposed to cool, wet soil conditions are also more susceptible to Sudden Death Syndrome (SDS) infection. Salto® and ILeVO® seed treatments can greatly reduce SDS severity infection by 70% or more and increase yield by 11% to 20% when compared to no seed treatment and heavy SDS pressure5.
While understanding or knowing the level of resistance your soybean cultivar has to certain pathogens may impact the level of response in plant survival and bushels produced, seed treatments should be viewed as table stakes if planting early.
4) What are the field attributes?
Areas of the field that may restrict root development, whether from compacted soils or poor drainage, can exacerbate disease development. Where inadequate drainage is a persistent issue that can’t be easily mitigated, it may better serve the producer to take those acres out of production because the cost of inputs may exceed revenue generated from grain.
It is important to know that most fungicide seed treatments do not control bacterial pathogens and do not control all fungal pathogens. In many instances, a complex of diseases can be found in fields with obvious symptoms. Most seed treatment products generally do not hinder B. japonicum’s ability to thrive if applied to the seed.
In-furrow systems are the recommended application method for B. japonicum if soybean seed is treated with Captan. If you are unsure, contact your crop protection representative to verify B. japonicum’s compatibility with your seed treatment.
Seed treatments can be an effective way to manage risk if soybean is grown continually, the environment is conducive to disease development, and a susceptible host is present. Many manufacturers offer products that also include an insecticide with the fungicide seed treatment. This can be an easy way to manage early-season insects that may attack before or shortly after germination.
If you have questions about seed treatments or if they are a fit for your farm, contact your local MFA or crop consultant for additional advice.
Next time you have to grab an umbrella at the door or flip on the wipers, keep in mind that April showers brings high hopes for a prosperous planting season in May.
1 Akley E., Rice C., Ciampitti I., Roozeboom K. Inoculation of soybeans: A good insurance policy. Kansas State University. Issue 663.
2 Leggett M., Dias-Zorita M., Koivunen M., Bowman R., Pesek R., Stevenson C., and Leister T. Soybean Response to Inoculation with Bradyrhizobium japonicum in the United States and Argentina. Agronomy Journal. 2017 109:1031-1038.
3 Sinclair J.B., and Backman P.A. Compendium of Soybean Diseases. 3rd ed. American Phytopathological Society.
4 Bradley C.A. Effect of Fungicide Seed Treatments on Stand Establishment, Seeding Disease, and Yield of Soybean in North Dakota. Plant Disease. 2008. 92:120-125.
5 Adee E.A. Effect of Saltro Soybean Seed Treatment on Sudden Death Syndrome in Kansas in 2019. Kansas Agricultural Experiment Station Research Reports. 2020. Pgs. 93-95.