No. 2/April 4, 1997
Fungicide Sead-Treatment Recommendations
As tillage decreases, the possibility of seedling blights increases, both for 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:
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 due to cooler and wetter conditions in reduced or no-till fields, seedling vigor or stands can be reduced if fields are planted too early. There may be a tendency for persons just starting to change tillage systems to plant too early because in their previous experiences spring field work 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, seed-to-soil contact can be affected by residue layers. 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 yields. Because the cost of seed treatments is low and the cost of replanting is high, seed treatment is usually an economical investment. Many years of evaluating seed treatments for soybeans throughout Illinois has shown that yields in most fields will increase 2 to 3 bushels per care, even if there are no obvious seedling blight problems present.
The choice of a seed treatment should be based upon the pathogens that occur in the fields. Specialized materials such as Apron or Anchor 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 blights is important in selecting the right materials. Or a combination may be used for a broader spectrum of control.
H. Walker Kirby, Extension Plant Pathology, (217)333-8414