Understanding Synthetic Seed Treatments - How To Maximize Return On Investment

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• Synthetic seed treatments help to establish crop stands by reducing the impact of important seedling diseases and pests 
• Not all seed treatments and rates are effective against all seedling pathogens and pests
• Early planted fields of continuous, no-till crops with drainage issues and a history of seedling pathogens are at the highest risk for seedling disease and pest issues

Ensuring even and timely seedling emergence is the first step in developing a crop with high yield potential. Smaller seedlings are less able to compensate for root damage caused by soilborne pathogens and pests than plants containing larger root systems and more foliar tissue. Pesticide seed treatments are one tool to assist producers in managing problematic seedling diseases and pests. 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 achieve a positive ROI (return on investment). This article will discuss seed treatments, present information on specific seed treatment performance, and provide information on determining the potential risk for seedling disease in corn and soybeans.

Basics of synthetic pesticide seed treatments

Seed treatments help protect the developing seedling during the highly vulnerable period from planting through early vegetative growth stages (approximately V1-V2). After planting, seed treatments 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 at least three to four weeks of protection for the seedling. After this point, fungicides or insecticides taken into plant tissues can be degraded, locked up by soil organic matter, or diluted in the soil and plant tissues. Roots also grow outside of the initial zone of protection in the soil with age. Remember, pesticide seed treatments do not fumigate soils and are only effective when they encounter an active fungal pathogen or insect.

When are pesticide seed treatments best used?

Research has shown that producers will experience a higher probability of achieving a positive ROI when seed treatments are used in fields that are at elevated levels of risk for important seedling diseases and insect pests. Table 1 provides a generalized risk calculator to help you determine the relative risk for seedling disease in a field, provided that the field has a history of seedling disease issues. In general, the risk for seedling diseases is greatest in early-planted, no-till fields with drainage issues. This is because these conditions often result in slower seed germination and seedling growth, while also favoring seedling pathogen and insect activity. There are few options for selecting corn seed treatments, as most brands are pretreated prior to shipment. However, we typically have more flexibility with soybean and small grain seed treatment product selection. Insects such as wireworms, white grubs, and seed corn maggots are major issues in field crop production systems. Risk for white grubs and wireworms can be assessed by evaluating at least ten sites per location following the protocols described in the article accessed through this link. Seed corn maggots are more likely to be problematic in fields that had ground worked, burndown, or manure applied two weeks before planting or less.  When selecting a seed treatment, make sure the active ingredients are labeled against the pests/diseases are concerned.  Higher rates may be needed in situations where pressure is severe or risk is elevated.

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

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 many fungicide active ingredients available in soybean. Ratings are based on the NCERA 137 ratings. Table 2 provides some examples of fungicide active ingredients and their performance, and Table 3 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.  Keep in mind that these lists are not all inclusive and are for educational purposes only.