• Soybean seed treatments can help improve seed germination, early season vigor and crop establishment which will contribute to improved yields at harvest.
• When used on soybeans, neonicotinoid seed treatments protect the developing seedlings from early season damage by bean leaf beetles, wireworms, seed corn maggots and white grubs.
• Basic fungicide seed treatment options provide early season protection from seedling diseases such as Pythium and Phytophthora, Rhizoctonia and Fusarium and add-on fungicide seed treatments can reduce from sudden death syndrome (SDS) infection and severity.
• Nematicide seed treatments help protect the roots from soybean cyst nematode (SCN) feeding by parasitizing the nematode, inhibiting nerve transmission or creating a protective barrier around the roots to repel nematodes.

Soybean seed treatments can help improve seed germination, early season vigor and crop establishment which will contribute to improved yields at harvest. Seed treatments provide a way for growers to manage the risk associated with early season pests and pathogens and protect their seed investment. They can often help to avoid the need for replanting when conditions are ideal for seedling pathogen infection or when early pests are present. Seed treatment categories include basic offerings such as fungicides and insecticides (F+I), added on seed treatments such as sudden death syndrome (SDS) and nematicide products (N), growth stimulants and inoculants among others. In this article we will review fungicide, insecticide and nematode seed treatments and discuss some of the active ingredients commercially available.

Insecticides: Insecticide seed treatments available for soybeans, all belong to the neonicotinoid class of chemistry. They affect the insect nervous system by binding to the nicotinic acetylcholine receptors. Acetylcholine is the major excitatory neurotransmitter in the insect’s central nervous system. Overstimulation of these receptors result in lethargy, paralysis and eventually death. Three active ingredients are available as soybean seed treatments; imidacloprid (Acceleron brand), clothianidin (Poncho) and thiamethoxam (Cruiser brands). Neonicotinoids have high water solubility and xylem systemic movement, which makes them great products to use as seed treatments. When used on soybeans, they help protect the developing seedlings from early season damage by bean leaf beetles, wireworms, seed corn maggots and white grubs.

Fungicides: Basic fungicide seed treatment options provide early season protection from seedling diseases such as Pythium and Phytophthora (oomycete pathogens), Rhizoctonia and Fusarium and add-on seed treatments can protect from sudden death syndrome infection. Although the ideal environment for infection will vary with the pathogen (i.e. Pythium and SDS are favored by cool and wet conditions at planting while Rhizoctonia and Fusarium are favored by warmer temperatures), it is important to know the active ingredients present in our seed treatment package. This is because not all actives are created equal, and active ingredients effective against Pythium and Phytophthora will not have activity against Fusarium and Rhizoctonia and vice versa. Likewise, the two active ingredients currently labeled for SDS (fluopyram and Pydiflumetofen) have no efficacy on the seedling pathogens mentioned above. These are some of the most effective active ingredients against seedling diseases*:

Pythium and Phytophthora: Ethaboxam, mefenoxam, metalaxyl, oxathiapiprolin (Phytophthora only). Be aware that some Pythium populations have become insensitive to mefenoxam and metalaxyl so efficacy will be reduced in these situations.

Rhizoctonia: Azoxystrobin, Fluxapyroxad, Sedaxane, Trifloxystrobin.

Fusarium: Ipconazole, penflufen, prothioconazole, fluxapyroxad, fludioxonil.

*This list is not all inclusive. For a full list of efficacy ratings across all commercial active ingredients visit: https://crop-protection-network.s3.amazonaws.com/publications/fungicide-efficacy-for-control-of-soybean-seedling-diseases-filename-2020-03-18-150238.pdf

Fortunately, the basic seed treatment products that we purchase will most likely contain more than one active ingredient; at least one for oomycete pathogens (Pythium and phytophthora) and one for Fusarium and Rhizoctonia. For example, Acceleron Basic contains pyraclostrobin, metalaxyl and fluxapyroxad so it should provide early season protection against all of these seedling pathogens. Cruiser Maxx Vibrance fungicide actives include fludioxonil, mefenoxam and sedaxane so this product will also have activity against all these seedling pathogens.

Sudden Death Syndrome: Two commercial seed treatment products are currently available against SDS; Ilevo with fluopyram as the active ingredient and Saltro with pydiflumetofen. Both of these actives are in the same class of chemistry (Group 7 SDHI fungicides).

Ilevo has been labeled for a few years and has proven effective at protecting yields in SDS favorable environments. It is highly systemic and is absorbed by the emerging seedling and translocated into cotyledons and unifoliate leaves. Because of its systemic activity, a temporary crop injury may result from its movement within the plant. Typically, a discoloration of soybean cotyledons that can turn yellow-brown and resemble herbicide injury can be observed in plants emerging from seeds treated with Ilevo. This injury is known as the halo effect. However, university trials have concluded that this temporary injury does not result in yield reductions. Be aware that some pre-emergent herbicides can increase the severity of this early crop injury. Saltro will be commercial for the first time in 2020 and should not result in the temporary injury we see with Ilevo. Both products have very similar labels and claim suppression of soybean cyst nematodes and other nematode species.

Nematicides: Several biological and synthetic nematicide seed treatments are available to manage soybean cyst nematodes (SCN). They can protect the roots from SCN feeding by parasitizing the nematode, inhibiting nerve transmission in the nematode’s nervous system or creating a protective barrier around the roots to repel nematodes. These seed treatments are described below:

Poncho Votivo: the active Bacillus firmus in Poncho Votivo colonizes growing roots providing a living barrier to nematode attack. Yield protection in the ranges of 0.5-7 bu/A have been observed under moderate to high SCN pressure.

Clariva: The active ingredient is the bacterium Pasteuria nishizawae, which is lethal to SCN. The spores of this bacterium attach to the nematode’s body, infecting and consuming the nematode internally. Once the body of the nematode ruptures, the bacterial spores are released, creating a new cycle of infection and a longer window of protection.

Avicta: The active ingredient, abamectin, is a fermentation product of Streptomyces avermitilis, which interferes with chloride channels in the nematode’s nervous system. Yield protection in the ranges of 0.5-8 bu/A have been observed with Avicta.

Aveo EZ: Contains the active ingredient Bacillus amyloliquefaciens Strain PTA-4838. The mode of action on SCN is unknown but it colonizes the roots of soybeans to reduce nematode reproduction.

Whatever your choices for seed treatments are, keep in mind that the likelihood of seeing a return on investment (ROI) increases as the pathogen pressure increases. Multi-year and multi-location trials on SDS seed treatments revealed that the probability of seeing a ROI was about 86% under severe SDS environments and only about 37% when no SDS is present (at a $7/bu soybean price and $13/A cost of seed treatment)¹. For more information on soybean seed treatment selection contact your local FS crop specialist.

¹ Seed treatment and Foliar Fungicide Impact on Sudden Death Syndrome and Soybean yield. CPN 5002 December 2019