Manage Problematic Pythium Species with a Novel Mode of Action –Vayantis

• Many species of Pythium have been identified in grower corn and soybean fields with differing levels of sensitivity to traditional Pythium fungicides.
• Vayantis^®, a fungicide seed treatment for Pythium, has shown to broaden protection across hard-to-control Pythium species at lower use rates than other fungicides.

Every year, thousands of acres of corn experience uneven growth and reduced final plant stands. Symptoms often occur in areas planted early, followed by a rapid drop in soil temperature and surplus rainfall for an extended time. These environmental conditions are conducive for seedling diseases such as Pythium to infect young seedlings, slowing growth, and even causing death in extreme situations.

Managing Pythium with Seed Treatments

Pythium is most commonly the first disease encountered by germinating corn and soybean seed. Fungicide seed treatments are generally used to protect germinating seeds from infection by soilborne pathogens. Most seed treatments are a combination of individual fungicides that offer protection against specific pathogens. Proper combinations of individual fungicides can offer broad spectrum protection against most common soilborne pathogens. Metalaxyl or mefenoxam (Apron XL^® fungicide) isbroadly utilized by seed companies for their excellent activity against Pythium species. Additional fungicides such as azoxystrobin, trifloxystrobin, fluoxastrobin and pyraclostrobin, are routinely added for protection against other pathogens, but when used in combination with metalyaxyl or mefenoxam, also provide supplemental Pythium protection.

Need for Multiple Modes of Action

Recent surveys of Midwestern corn and soybean fields have been carried out to better understand the diversity of Pythium species present as well as their sensitivity to common seed-applied fungicides. Multiple species of Pythium were routinely observed with varying levels of pathogenicity to both corn and soybeans. Researchers in OH¹ and IA² have reported a subset of Pythium species isolated which have differing levels of sensitivity to the commonly used seed-applied fungicides mefenoxam, azoxystrobin and trifloxystrobin. Although these fungicides continue to offer good levels of protection across the Midwest, when used individually, they may not always inhibit growth of all pathogenic Pythium species found within the soil. It is likely that without the use of additional new fungicide modes of action, stand establishment could become more challenging in fields over time.

Vayantis Provides Unique Mode of Action

A recently registered fungicide from Syngenta Seedcare branded as Vayantis (picarbutrazox) provides a new level of Pythium protection and is now being used on all Golden Harvest^® corn hybrids. In combination with CruiserMaxx^® Vibrance^®, Vayantis enhances protection in fields where unique Pythium species have become harder to manage. Other seed companies are utilizing another mode of action, in addition to metalaxyl, that was introduced in 2014 and is branded as INTEGO^® (ethaboxam). Both Vayantis and INTEGO fungicides have demonstrated improvements in protection, beyond metalaxyl alone. Although due to the diversity of Pythium species that exist, and differences in sensitivity of those species to different fungicides, there can be noticeable differences in performance between these two products. Syngenta screened a large collection of Pythium isolates collected across the Midwest for sensitivity to Vayantis, ethaboxam and mefenoxam as shown in Graph 1. The mean effective concentration (EC) 50 shown represents the EC at which fungal growth is inhibited by 50%. Lower values observed with Vayantis illustrate the reduced use rate needed to control Pythium as compared to the other fungicides. The sensitivity test also illustrates how species such as P. torulosum and P. aphanideramatum were harder to manage and required higher use rates with ethaboxam, whereas Vayantis offered consistent activity at a much lower use rate across all 18 species commonly found in the Midwest.

Vayantis Field Trial Learnings

Field trials designed to evaluate stand establishment of seeds treated with different fungicides found similar results as lab screenings when “insensitive” Pythium species were present. Figure 1 compares field emergence of seed treated with metalaxyl and fluoxastrobin at rates commonly used in Bayer’s Acceleron^® seed treatments. Good emergence was observed in rows with native soil pathogens, although few plants survived in rows exposed to insensitive Pythium species. In the neighboring plot where seed was treated with Vayantis, good stand establishment was observed in both rows with and without insensitive Pythium species being present. In the same trial, emergence of seeds treated with metalaxyl, azoxystrobin and ethaboxam, commonly used in LumiGEN^® seed treatments by Corteva Agriscience, had partial stand establishment when exposed to “insensitive” Pythium species (Figure 2). Although emergence was improved with ethaboxam, there were fewer emerged plants than when seeds were treated with Vayantis. Neither example, other than those treated with Vayantis, represented a commercially acceptable plant stand and would have required replanting if it was an actual field scenario. There also appears to be some level of “cross-resistance” between ethaboxam and metalaxyl to the Pythium isolate present in this field trial. There are no known examples of cross resistance for Vayantis.

Research trials have repeatedly demonstrated that uniformity of seed emergence and plant growth is almost as equally important as achieving target final population. One Golden Harvest Agronomy in Action research seed treatment trial at Clay Center, KS, encountered stressful emergence conditions that resulted in both decreased emergence and uniformity. Seed treated with CruiserMaxx^® Corn 500 with Vibrance^® containing the oomycete-controllings fungicides mefenoxam and azoxystrobin were compared to seed additionally treated with either ethaboxam or Vayantis. The addition of Vayantis increased plant final stands and decreased the total number of weak plants (plants 1 or more growth stages behind normal) (Graphs 2 and 3). The combination of more plants and improved uniformity resulted in a 16% increase in yield potential in this trial (Graph 4).

Summary

Pythium is one of the leading causes of yield loss in corn. It is commonly the first pathogen seeds encounter each spring and frequently is thought of as the most significant corn seed/seedling disease. Pythium commonly causes reduced plant stands, weaker, stunted plants and, ultimately, reduced yield potential. Species of Pythium that are less sensitive to some oomycete-controlling fungicide chemistries have been observed in Midwestern fields, although the novel mode of action provided by Vayantis has not been found to be cross-resistant to the same species. Paired with other fungicides that are active against Pythium, Vayantis can provide a more reliable way to manage Pythium.

If you have questions about tackling Pythium and other hard-to-control pests, please reach out to your local Golden Harvest Seed Advisor or agronomist.