Cooperative
Extension
Service


University of Illinois
at
Urbana-Champaign


No. 10/May 29, 1998

Seed-Treatment Fungicides for Soybean

With weather patterns indicating the continuance of scattered showers for at least the next week or so, soybean producers will want to consider seed treatments, at least in areas of heavy residue from previous crops. Cool or wet soils increase germination time and allow fungi more opportunity to colonize seeds.

When selecting seed treatments, you have many options. Our experience has been that seed treatments are the most beneficial when seeds or seedlings are stressed during the first 10 to 14 days after planting. Examples of stress include heavy rains, crusted soils, compaction, deep planting, cool soil, improperly set planters, reduced seed quality, and very dry soils.

The choice of a seed treatment also depends upon the target pathogen or pathogens. Typically, these are either water molds (so called because they produce a swimming spore when soil flooding occurs) or other fungi. The water molds include Pythium and Phytophthora species. The other fungi are mainly Rhizoctonia, Fusarium, and Macrophomina species.

Water molds produce a soft rotting of the seed, or damping-off, before or after emergence. With damping-off (named for the wet or damp conditions that favor disease development), a dark brownish or blackish soft rot girdles the seedling stems, and plants die. There is no recovery from these infections.

Rhizoctonia and Macrophomina produce distinct reddish lesions along one side of the stem and do not commonly girdle stems. Plant growth is reduced in the early season, but death of plants is not common in Illinois. With Fusarium, a generalized dry rotting of the roots may be seen, as well as some reddening of the interior root portions. Fusarium is not a common problem in Illinois and is not seen unless severe stress is placed on the germinating seed and seedling. Seedlings infected with Fusarium die.

Suggested seed treatments and diseases controlled are listed in Table 1. This list is not complete and is given for illustrative purposes only. Check with local dealers to determine what products are available in your area. Also, consult the Illinois Agricultural Pest Management Handbook for further information.

Table 1. Suggested soybean seed treatments and diseases controlled

Diseases controlled Common name Product name of fungicide Comments
Phytophthora Metalaxyl Allegiance
Pythium Metalaxyl Apron
Pythium Mefanoxam Apron XL
Rhizoctonia and other seedling blightsPCNB PCNB
Carboxin Vitavax
Captan Many
Thiram Thiram
Thiabendazole (TBZ) Many Controls Phomopsis (pod and stem infections
Maneb + Captan Granox P-F-M
Chloroneb + Metalaxyl Nu-Flow AD Controls Pythium/
Phytophthora
TBZ + Captan Many
Chloroneb Chloroneb 65W
Thiram + Carboxin Many
Bacillus Subtilis Kodiak Use with a chemical seed treatment
Other biologicals Many

H. Walker Kirby (kirbyw@idea.ag.uiuc.edu), Extension Plant Pathology, (217)333-8414