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 blights||PCNB ||PCNB|
| ||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/|
| ||TBZ + Captan ||Many|
| ||Chloroneb ||Chloroneb 65W|
| ||Thiram + Carboxin ||Many|
| ||Bacillus Subtilis ||Kodiak ||Use with a chemical seed treatment |
| ||Other biologicals ||Many|
H. Walker Kirby (firstname.lastname@example.org), Extension Plant Pathology, (217)333-8414