Now is the time to begin looking for soybean seedling blights. Seedling blights are caused by a number of soilborne fungi that infect the roots of soybean seedlings, causing a root rot that gives the aboveground portion of the plant a blighted appearance. Dave Feltes, IPM Educator at the Quad Cities Extension Center, reports seedling blights in area fields. |
Although you can typically expect to see root rot diseases such as Pythium and Phytopthora in low, poorly drained areas, they are not always specifically limited to those areas, especially taking into consideration the wet weather conditions we have experienced thus far in the growing season. Both of these diseases have similar symptoms: brown, rotted roots with an absence of secondary roots. Also, both of these diseases typically kill the seedling. They are indistinguishable in the field and must be identified in a lab. This is important for future management options. While fungicide seed treatments are available that effectively control both of these diseases, only Phytopthora can be managed by the use of resistant varieties.
Other seedling root rots to look for now are Fusarium and Rhizoctonia root rot. These two fungi cause what is termed a "dry rot." Both can cause a reddish-brown canker, usually at the soil line, and a dry-type rot of the roots. Like the wet rots, the dry rots are virtually indistinguishable in the field. To further complicate the situation, these two fungi are often found together. Both Fusarium and Rhizoctonia seedling blight are less environmentally limited than Pythium and Phytopthora. In other words, you won't just find them in the wet spots in the field. Given optimal growing conditions, seedlings can recover fairly well from the dry rots. Fungicide seed treatments are an effective option for management. For more discussion of seedling root rot disease symptoms, see issue no. 7 (May 7, 1999) of the Bulletin.--Suzanne Bissonnette