Crop performance testing results are released annually through the activities of SDSU Extension and the South Dakota Agricultural Experiment Station at SDSU.
Soybean harvest is nearing as most, if not all, soybeans have turned color or dropped leaves. Fall time is the best time of year to sample and test the soil for soybean cyst nematode (SCN), the number one silent yield robber of soybean.
A new soybean virus called Soybean vein necrosis virus (SVNV) was detected in South Dakota soybean fields in Davison and Union counties. Symptomatic plants were sporadic and found along the field borders. Infected plants showed mild to moderate severity.
A few fields scouted last week had soybean plants dropping leaves prematurely. Upon checking these plants, they were found to be infected with charcoal rot. Areas in a field with plants droppings leaves earlier than normal should be scouted to rule out diseases such as charcoal rot, brown stem rot, or sudden death syndrome.
Alfalfa mosaic virus-like symptoms were found at a very low incidence in a few soybean fields scouted last week. Leaves from the potentially infected plants were subjected to laboratory test and were confirmed to be positive for Alfalfa mosaic virus (AMV).
Last week, sudden death syndrome (SDS) was confirmed in Lincoln, Turner and Union counties. Most of the fields found with SDS had very few scattered plants showing symptoms, with the exception of one field in Lincoln County which had a moderate level of SDS.
Brown stem rot (BSR) was found in a few soybean fields in Brookings and Moody counties the week of September 4 at very low incidence. BSR is a late season disease and its symptoms can look like sudden death syndrome.
White mold was observed just starting to develop in several fields scouted in Brookings, Deuel, Moody, and Minnehaha counties last week. These counties have received frequent rainfall events and cooler temperatures, which are conditions that favor white mold development.
On September 12, SDSU Extension will hold a soybean disease ID field day to help growers, crop consultants and agronomists get familiar with diagnosing mid-season soybean diseases.
For the last two years, we have been hearing of pyrethroid resistant soybean aphids in our neighboring states of Minnesota and more recently Iowa. These pyrethroid resistant soybean aphid populations were initially detected due to field wide failures of foliar applied pyrethroid insecticides.