ISA Soybean Summit: Keeping soybean seedling diseases in check

BLOOMINGTON, Ill. — Soybean seedling diseases have been referred to as the hidden yield-robbers, as well as other terms not fit to print, and similar to the battle against weeds, require an integrated management approach to control.

Nathan Kleczewski, Growmark pathology and entomology technical specialist and former University of Illinois field crop pathologist, gave a rundown of soybean seedling diseases and their management at the Illinois Soybean Association-hosted virtual Soybean Summit.

Soybean diseases common across the Midwest include Sudden Death Syndrome, Pythium, Phytophthora and Red Crown Rot.

“Seedling diseases are all soil-borne and do not spread by launching spores into the air. These persist in the soil and are going to be attacking emerging soybean seedlings before or after they start to emerge,” Kleczewski said.

“Seedling diseases all are favored by wet periods at planting from emergence through the early vegetative phases and cause the death of a seedling or reduces root growth and development.

“Managing seedling disease typically is based on facilitating the emergence of the seedling and the development of true leaves because as soon as those true leaves pop out and those leaves start to produce photosynthate, they’re going to allow the root systems to grow and expand and then out any potential infections. That’s when we see the benefits of seedling management are really promoting the germination and growth early on in the season.”

Extensive multiple years of research across many platforms shows the most efficient way to maintain productivity and minimize seedling disease issues is by utilizing an integrated pest management strategy.

Cultural practices to manage seedling diseases include crop rotation, irrigation management, planting date and residue management.

“Host resistance in cultivars can be used when appropriate and only is applicable to certain types of seedling diseases such as Sudden Death Syndrome and Phytophthora. Seed treatments specific to diseases needing control can be useful, as well, but we have to keep in mind how those work and how to select them,” Kleczewski said.

“Biological control organisms for control can be inoculants and manipulate the soil environment so that there’s more diversity in the soil. The thing we have to keep in mind with biological control is those are living organisms, too, so we don’t tend to see as consistent of a response. But anytime we’re improving the diversity of the soil microbes it helps our management of our pathogens because soil pathogens are not typically very good competitors.”

Seed Treatments

Fungicide seed treatments help improve the seed germination and provide initial protection of the developing seedling through V2 or so.

“They typically work for three to four weeks and then after that point you can really be expecting to be providing much benefit. They are not fumigating soil. They are just existing in the immediate root zone. Some of those active ingredients depending on their how they work can be taken up into the germinating seedling tissue and move into the foliage, as well as into new roots,” Kleczewski said.

“But we have to remember that these are not just going to kill all the pathogenic organisms in the soil. If those organisms aren’t active at the time the seedlings aren’t planted, like because the moisture is not right or the temperature is not right, those seedlings won’t have an activity and they’re definitely not going to cure dead seed.”

There are several factors that impact fungicide seed treatment utility and efficacy.

There are fungicide seed treatments with specific modes of action they are targeting, their mobility in the soil, if they are systemic or not, and how broad of spectrum they have. Some active ingredients only affect on pathogen while others may affect multiple pathogens.

“Soil characteristics are also important. In particular, organic matter that will lock up these active ingredients once it comes into contact with them. Typically the more organic matter you have, the less these chemicals will move in the soil and the less activity they will have,” Kleczewski said.

“Soil temperature, soil texture and all of those other things can have impacts. One thing we have to keep in mind is just like with fungal pathogens we encounter on the foliage, we do get resistance in soil pathogens, as well.”

Return On Investment

Not unlike countless other decisions made on the farm, there’s always the question of will using a seed treatment to protect against soybean seedling disease payoff.

“If you’re thinking about things that will increase your risk for potentially needing a seed treatment and breaking even or having improvements of profitability when you use these things these are the five big rungs on the ladder,” Kleczewski explained.

“Know the history of seedling disease in that field. If you confirm it’s an issue in the field, you know what you’re dealing with.

“Planting a susceptible cultivar comes into play especially with Sudden Death Syndrome and Phytophthora. Continuous soybean production increases seedling disease populations or pathogenic populations.

“In no-till production, a lot of times soybean residue can host some of these diseases like charcoal rot. It can also serve as a resource for some of these pathogens, in addition to helping to hold in more moisture in the soil.

“The cost of seed and seed treatment, yield and sale price is really the big thing. How much does it cost to put that seed into the ground along with that treatment and what’s the benefit you’re getting back in terms of protecting that yield.”