Recommendations on Fungicide Seed–Treatments

April 2, 1999
Many weather forecasters predict this spring to be cooler and wetter. Whether or not you believe any of these long–range weather prognosticators, cooler and wetter springs can increase seedling blights in corn and soybeans. Environmental conditions, as well as practices such as tillage, can influence the development of seedling blights and rots.

As tillage decreases, the possibility of seedling blights increases for both corn and soybeans. The presence of crop residues, plus changes in planting patterns, may affect both stands and final yields. These effects come from a variety of factors, including the following:

  1. Cooler and wetter soils. Crop residues act as a mulch layer, increasing water–retention capacity and keeping soils cooler. This effect is beneficial late in the season but may increase the activity of early season pathogens such as Phytophthora and Pythium fungi. Both of these root–rotters are favored by cool soils and wet conditions. In addition, these soil conditions can cause a delay in emergence that may permit other fungi such as Rhizoctonia to infect the emerging seedling.
  2. Planting time. With delayed germination possible because of cooler and wetter conditions in reduced or no–till fields, seedling vigor or stands can be reduced if fields are planted too early. There is a tendency for persons just starting to change tillage systems to plant too early because, in their previous experience, spring fieldwork was needed. With no–till especially, farmers do not need to be in fields as early because there are no soil operations to do.
  3. Poor seed–to–soil contact. Unless planters are frequently checked and adjusted, residue layers can affect seed–to–soil contact. Some seed may be planted too shallow while others are placed too deep. This stress can influence emergence and stands.

Even with modern hybrids and soybean cultivars, stress conditions can reduce stands and affect final yield. Because the cost of seed treatment is low and the cost of replanting is high, seed treatment is usually an economical investment.

The choice of a seed treatment should be based on the pathogens that occur in the fields. Specialized materials such as Apron XL or Allegiance control Phytophthora and Pythium but have no effect on other pathogens. Other seed treatments control most pathogens (particularly Rhizoctonia) but have little effect on Pythium or Phytophthora. Thus identification of the seedling blight is important in selecting the right materials. A combination of materials may be used for a broader spectrum of control.--JT
Author: Joe Toman