hand holding soybean seedling
EARLY-SEASON RISK: If you plant soybeans early into wet soils without seed treatment, you risk various kinds of stand problems. Disease and herbicide injury contributed to this seedling’s problems.

Should you eliminate soybean seed treatments?

Soybean Source: With so many seed treatments, deciding on one is a challenge.

Take a guess. What’s one of the fastest-growing segments of the crop production and protection industry today? A few hints: It’s a market that barely existed in the 1990s. Now, probably over 90% of our seed corn and 75% or so of our soybean seed use one or more of these products. Demand for them is predicted to rise around 11% per year over the next five years, reaching a global market value of nearly $10 billion in 2021. You’ve probably guessed by now: seed treatments. Given that most of our seed treatment decisions are made on soybean acres, let’s look at how to prioritize our investment in soybean seed treatments.

Deciding exactly what seed treatments you might benefit from is challenging; we have a lot of choices now. Fungicides, insecticides, nematicides, inoculants, growth promoters, micronutrient mixtures, biologicals and other amendments are available. The good news is most of our choices can be made near planting time since most seed dealers can customize your treatments on-site. Combining knowledge of each of your soybean field’s agronomic challenges, your soil conditions at planting time and a decent short-term weather forecast can help dial in what treatments may be a good idea.

Early-season stresses
Every year we work to plant as early as we can within the recommended planting windows. While early planting typically puts us in the best position to maximize yields, it can also expose soybean stands to early-season stresses. This is where seed treatments start to become a better bet.

The primary role of most seed treatment components is to improve stand establishment and overall plant health by curbing the effects of early-season stresses like diseases and insects. Because there are too many individual products to go into detail on each one, we’ll discuss the main categories of seed treatments.

Seed-applied fungicides suppress stand-reducing diseases. The length of protection and spectrum of diseases suppressed varies with products and application rates. Prime candidates for fungicide seed treatments include no-till and reduced-till fields, early-planted fields, fields planted to beans-on-beans, fields with cool or wet soils, or other conditions that may slow germination, and fields with a history of seedling diseases.

One key to maximize performance of fungicide seed treatments is to work with your seed supplier to match the right combination of fungicides to the disease problems you expect to encounter. While it’s tough to predict which of the major seedling diseases we may fight in any given year, pythium, phytophthora, fusarium and rhizoctonia are typically considered the primary culprits to watch for.

Double-check that you are using seed treatments that are effective on those four pathogens, and if you have fought specific ones in the past, be sure to focus on products that are strong on those particular pathogens. We have a good variety of active ingredients to pick from, each with their own strengths; your seed supplier can help choose the combination of fungicide active ingredients to fit your needs.

Another pathogen we fight, sudden death syndrome (SDS), has hit yields hard in fields across much of Iowa the last few years. While just one part of an integrated pest management plan against such a devastating disease, recently-launched seed treatments like ILeVo and Mertect have given us much needed tools in the fight. Several years of company and university testing, combined with having seen it in a lot of clients’ fields under SDS pressure the last three seasons, has demonstrated that if you are fighting SDS, ILeVo is a good investment. I don’t have as much experience with Mertect and our data is limited to date, but your local chemical rep might have additional data to discuss with you.

While there is a lot of work to be done in the battle against soybean cyst nematode, the emergence of nematicide seed treatments has added firepower to supplement SCN-resistant soybean varieties. This is a relatively new and growing segment of seed treatments, so there is limited research I could find outside of our own Dr. Greg Tylka’s work. Looking at neighboring states’ data may add some insight, and you may also want to ask your seed agronomist for their latest information on nematicides. Here are a few takeaways I got from looking at work Tylka’s team has done over the last several years:
• In trials on SCN-infested fields, I found few significant differences between yields of the paired treatments, with and without Clariva, and with and without Ilevo.
• The overall high yields (and limited yield differences across the plots) were likely an indication of the relatively mild conditions that occurred the last few seasons with respect to SCN damage.
• These types of results illustrate how weather can be one of the biggest (and most unpredictable) factors in returns from seed treatments.

My bet is that if we are under weather stress in 2017, which would increase potential SCN damage, we’ll learn a lot more about nematicide seed treatments. Of course that doesn’t help us make decisions now; so unless a field has significant SCN numbers, it is hard for me to put a priority on investing in this segment of seed treatments. With the fading efficacy of our primary SCN resistance gene, PI88788, I do see this segment of the seed treatment market growing in the very near future. Have I mentioned lately that we need to be regularly testing our fields for SCN?

Skipping this component of seed treatments is a place I hear many growers talk about cutting back. I don’t try to change their mind in most cases. Published research has shown while neonicotinoids (the primary insecticide in seed treatments) can be effective in controlling sporadic and inconsistent early-season soybean threats, such as wireworms, seed corn maggots or white grubs, they lose effectiveness well before midsummer. That’s usually when the most potentially destructive soybean pest, the soybean aphid, begins to colonize soybean fields across the Midwest. I just don’t run into many soybean fields that we suffer significant stand loss from the “early season” pests mentioned above.

Adult bean leaf beetles are another occasional pest in newly emerged soybeans that insecticide seed treatments can be effective on, but this pest rarely causes more than cosmetic injury since soybean plants are so resilient and can tolerate a lot of early-season damage without suffering economic loss.

There are some situations where an insecticide seed treatment on soybeans is almost always a good investment, though:
• Fields transitioning from pasture, Conservation Reserve Program or other grasslands to soybeans. These fields tend to have higher populations of long-lived soil pests, such as wireworms or white grubs.
• Fields with recently incorporated manure, green cover crops, or a lot of weeds. These fields tend to be more attractive to seed corn maggots because females lay eggs in rotting organic material.
• Specialty (food-grade or seed) soybeans. Early-season insect pests can vector diseases that affect crop quality (bean leaf beetles transmitting bean pod mottle virus, for example).

Compare risk vs. reward
Soybean seed treatments: Can we afford to use them? Can we afford not to? While the choice isn’t always easy, selecting the right seed treatments may prove worth the effort. Because they are applied to seed in anticipation of problems, seed treatments offer risk management. We’ve talked about where seed treatments are likely to be a good bet. But when can we gamble on taking a pass on using them if we don’t have many of the risk factors we’ve discussed here?

If we get delayed later into spring with planting dates and we are planting into warm, well-drained soils, our odds of having soybean seedling disease problems decrease. If current conditions and the weather forecast are favorable for rapid emergence and strong early growth for a couple weeks after planting, then the odds of a return on the seed treatments can go down. On the other hand, weather forecasts are far from perfect; a cold spell or significant rainfall can put us back in the position where treatments may protect our seed investment.

Another piece of the puzzle is replant protection. Depending on what seed treatments are on your original planting, companies may offer substantial discounts on replant seed; in some cases, they may cover all of the seed cost.

Even with all the information we’ve covered here, seed treatment decisions are still an inexact science. Hopefully, what we’ve talked about will help you prioritize which types of seed treatments (out of the many choices) are most likely to benefit your operation.

McGrath is the On-Farm Research and Extension coordinator for the Iowa Soybean Research Center at Iowa State University.


Other types of seed treatments

Biologicals, growth promotors, and seed-applied nutrients are soybean seed treatments we are hearing more about and seeing more of them being marketed.

This sector of soybean seed treatments is one that quite honestly we need a lot more independent data on. But given the sheer number of products on the market and how quickly they evolve, it is hard to keep up. To illustrate the challenges, I’ve participated in testing a dozen or more new products over the last few years. Some were inconsistent, some offered marginal benefits and some offered very encouraging yield results over the first year or two of testing. Yet very few of any of the products tested either made it to, or are still on the market. It’s frustrating to see good results and then have the product shelved.

My takeaway point: While not every product may have a role in your farming operation, there are some good ones out there that may have a fit. Don’t be afraid to give them a trial run by testing in a few fields. A good place to start sorting through them is to ask what is the cost per acre compared to the yield increase expected; and what are the odds of getting that expected yield increase, i.e. how consistent has the product proven to be in your area? Your local seed agronomist may be able to access some data or may have insight on products that look promising in your region.

When are inoculants needed?
I wrote an in depth article in Wallaces Farmer on soybean inoculants in winter 2013 after coming off the drought of 2012. For more information, look for that article. The short version is since the cost of inoculation is usually pretty low, well under a bushel per acre, there are a couple of situations where we can easily give them the green light.

In fields that haven’t had beans for several years, or where significant parts of a field were flooded or had ponds for more than a few days, the risk of yield loss is high enough to make treatment a good bet. Outside of those situations, most of our fields have plenty of rhizobia, so the addition of inoculant for that purpose typically isn’t justified. As with most agronomic questions though, “It depends.”

A complicating factor is many of today’s commercial inoculants are promoted as having novel or new strains of rhizobium that can increase yields even under normal circumstances. Other inoculants are co-packaged with growth promoters, micronutrients, bio-fungicides or other ingredients and are along for the ride. Take it field by field, product by product, and lean on your experiences and insight from your seed dealer to help fine tune your approach to inoculants in these fields.

Where to get more information
A great place to find information on a number of seed treatments is the Iowa Soybean Association (ISA) On Farm Network Replicated Strip Trial Database. Their database contains summaries of individual strip trials following On-Farm Network protocols. The summaries include essential management information, yield data and imagery. The site allows users to query by year, crop, trial type/detail and location. I found the data from 130 trials on a wide range of seed treatments from 2006 to the present to be pretty interesting (and easy to digest even for a guy like me who finds “data” boring). To pique your interest, I like to share these tidbits:
• Across the 130 trials, there was a cumulative average yield response of 0.3 bushel per acre to the various seed treatments.
• The largest yield response in a trial was 6.1 bushels per acre.

One might think, “Wow, there must have been a lot of pest pressure for there to be a 6.1-bushel difference between treatments.” I’ll let you interpret the details, but the yields in this trial were 75.2 vs. 81.3 bushels per acre. I found quite a few other interesting trials to look at, particularly over the last few seasons. You can take a look at their trials at isafarmnet.com/onlinedb/index.php.


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