Understanding Fungicide Seed Treatments

Research has shown that producers will experience a higher probability of achieving a return on investment when seed treatments are used in fields that are at elevated levels of risk for important seedling diseases

• Fungicide seed treatments help to establish soybean stands by reducing the impact of important seedling diseases
• Fungicide seed treatments deliver approximately three weeks of protection to the seed/seedling
• Not all fungicide seed treatments are effective against all seedling pathogens
• Early planted fields of continuous, no-till soybeans with drainage issues and a history of seedling pathogens are at the highest risk for seedling disease issues

Fungicide seed treatments are one tool to assist producers in managing problematic seedling diseases. However, seed treatments are not always needed and are not created equal. Understanding the factors and conditions where these technologies may provide the greatest benefit will help with achieving a positive ROI. This article will discuss seed treatments, present information on specific seed treatment performance, and provide information on determining potential risk for seedling disease in corn and soybeans.

Basics of Fungicide Seed Treatments

Fungicide seed treatments help protect the developing seedling during the highly vulnerable period from planting through early vegetative growth stages (≈V1-V2). After planting, seed treatment fungicides protect the seed coat and may move into a limited area of soil around the seed. Many active ingredients can be taken up by the seedling roots and moved to developing stem/foliar tissues through the conductive tissues of the plant as the seedling develops. Work has shown that seed treatments can provide approximately three-weeks of protection of the seedling. After this point, fungicides taken into plant tissues are degraded, locked up by soil organic matter, or diluted in the soil and plant tissues. Roots also have grown outside of the initial zone of protection in the soil with age. Remember, fungicide seed treatments do not fumigate soils, and are only effective when they encounter an active fungal pathogen.

When are Seed Treatments Best Used?

Research has shown that producers will experience a higher probability of achieving a return on investment when seed treatments are used in fields that are at elevated levels of risk for important seedling diseases. Table 1. has a generalized risk calculator for helping you determine the relative risk for seedling disease in a field, provided that the field has a history of seedling disease issues. In general, risk for seedling diseases are greatest in early planted, no-till fields with drainage issues. Any factor that slows seed germination, emergence, and initial growth favors seedling disease development. There are few options for selecting corn seed treatments, as most brands are pre-treated prior to shipment. We typically have more flexibility with soybean seed treatment product selection.

What Soil Pathogens May be Encountered?

Table 2. lists the potential seedling diseases that could impact your corn and soybeans, conditions that favor development, and other factors that may affect their impact on the current crop. Diseases caused by oomycetes (Pythium and Phytophthora root rot) are favored by poorly drained soils saturated with water, whereas other diseases (e.g. Rhizoctonia root rot) are favored by moist, but not saturated soils. All of these pathogens are soilborne, meaning that they infect from the soil at/near planting, and do not move long distances on air currents like some other diseases. These pathogens all overwinter in soils as tough overwintering structures or in/on crop residue.

Table 1. Use this table to help you in determining the relative risk for a seedling disease to be an issue, and help you decide if a fungicide seed treatment may provide a potential benefit. For this table to work, the seedling pathogen MUST be present in the field. This is just a guide and does not guarantee a particular disease will or will not be a problem in a given field/season. High risk = 12-15; Moderate risk 8-11; Low risk 7 ≥.

Score interpretation: High risk >9; Medium risk: 5-8; Low risk <5. *Susceptible cultivar only included if Phytophthora or SDS are major disease of concern in soybeans. Field tolerance to Phytophthora is not active in soybeans until V1 (First trifoliate).

Table 2. Pathogens causing seedling diseases that are frequently encountered in corn and soybeans.

Seed Treatments Differ in Efficacy

Remember, not all fungicide active ingredients are effective against all pathogens. Some are specific for certain groups of fungi (e.g. oomycetes such as Pythium and Phytophthora) or even specific species of fungi (e.g. Fusarium virguliforme). The table below provides the relative performance of fungicide active ingredients currently available in soybean. Ratings are based on the NCERA 137 ratings. Table 3 provides some examples of fungicide active ingredients and their performance, and Table 4 provides a list of some trade names of seed treatments in corn and soybean and their active ingredient composition. There are numerous active ingredients and trade names available, so these lists are all inclusive and are for educational purposes only.

Table 3. Examples of fungicide active ingredients and relative performance against target fungal groups. 5 = excellent, 0 = not recommended. Blank = not enough data or not labeled. *This ingredient varies in performance with Pythium species. Pythium composition in a field may impact overall efficacy.

Table 4. Trade names of example seed treatments and active ingredients for corn and soybeans.