Effects of Fungicide and Planting Date on Soybean Productivity


  • To optimize yield potential, soybean growers often plant as early as possible within the recommended planting window for the region. Such early planting; however, runs the risk of predisposing seeds and young seedlings to early-season stressors such as insects, diseases, and cool, wet soils, which can substantially affect stand establishment and overall plant and field health. To avoid these conditions, growers can plant later when soil conditions are optimal for germination and growth. Both options have effects on field performance and suitability/convenience for the whole farm operation.
  • It is necessary to protect established plants from stressors that ultimately reduce yield potential. The application of a fungicide can protect soybean plants from foliar diseases and increase overall plant health, which can lead to increased grain yield.
  • Yield responses observed from the application of a foliar fungicide greatly depend on seed product selection, as individual products respond differently to a fungicide application. 
  • The objective of this trial was to evaluate the impact fungicide application and planting date have on soybean productivity.



LocationHuxley, IA   
Soil Type Clay loam  

No tillage 

Planting Date4/27/20,  5/13/2020   
Harvest Date10/14/20 

Potential Yield
Seeding Rate



  • Three soybean products were used for the trial:
    • 2.0 maturity group (MG) product 
    • 2.4 maturity group (MG) product
    • 2.9 maturity group (MG) product
  • Each product was planted on two different dates:
    • April 27, 2020 (early planting date)
    • May 13, 2020 (late planting date)
  • Delaro® Complete fungicide was applied at a rate of 8 oz/acre at the R3 growth stage. 
  • Trial was carried out in 30-inch row spacing, 4 rows/treatment with 5 replications.
  • Tillage and weed management were the same for all treatments.


image Figure 1. Yields of three soybean products averaged across planting dates and fungicide applications. Average represents the average yield of all the three products.
image Figure 2. Effects of planting date and fungicide application on the yields of three soybean products. Data represents yields averaged across fungicide applications. Average represents the average yield of all products at that planting date.
image Figure 3. Effects of fungicide application on planting date and yields of three soybean products. Data represents yields averaged across the two planting dates. Average represents the average yield of all products at that fungicide treatment.

  • At the trial site, yield increased as the relative maturity of products increased (Figure 1).
  • Late planting date out-performed early planting date in the 2.0 RM and 2.9 RM products but not in the 2.4 RM product. On average, there wasn’t much difference in yield between the planting dates (Figure 2).
  • Fungicide application substantially improved yields in all the products, with an average yield gain of 6 bu/acre (Figure 3).
  • Without a fungicide application, yields were the same, however, with fungicide application, late planting slightly out-performed early planting (Figures 2 and 3).



  • In all production regions, products within the appropriate maturity group should be selected to optimize yields. The 2.9 RM product is the full-season product selected for the trial location and yielded the highest (Figure 1).
  • For this site, early planted soybeans have historically yielded higher than late planted soybeans. For this trial year, the trial location experienced cold and wet conditions after the early planting date. This resulted in protracted germination and emergence, a situation not experienced by the late planting. This, in part, may explain why early planting did not out-perform late planting this year (Figure 2).
  • Over the past several years, foliar fungicides have consistently improved soybean yields at the trial site. In general, there wasn’t a disease outbreak at the trial site; however, there were minor incidences of sudden death syndrome (SDS), frogeye leaf spot, Septoria brown spot, and Cercospora leaf blight in both the fungicide sprayed and unsprayed plots. Also, the site was in the path of the derecho that hit Iowa in August of 2020. 
  • With the current grain price of about $10/bushel, a 2 to 3 bu/acre yield gain is needed to cover the cost of the fungicide application. Thus, fungicide was cost effective for all the treatments in this study.
  • Crop yield response to production inputs can be highly variable, often impacted by the environmental conditions during the growing season. Farmers are therefore advised to consult their trusted crop advisors when making such decisions.


This browser is no longer supported. Please switch to a supported browser: Chrome, Edge, Firefox, Safari.