Soybeans scouted last week were found with white mold and sudden death syndrome. These two diseases develop starting at the soybean flowering growth stage and can occur throughout the rest of the soybean growing season.
Last week, we mentioned that gall midge larvae are being found more frequently this year in soybean. We also noted that where they are present, they seem to be causing a lot of issues with soybean development.
Soybean aphid populations are continuing to persist and increase in South Dakota. Hot spots can be observed from the Southeast to the Northeast corners of the state. For this reason, scouting should continue and extra attention should be given to fields that are close to the 250 aphid/plant threshold.
In previous years, the gall midge has been observed in South Dakota soybean fields. We originally didn’t think that the gall midges had much of an impact on plant health.
Last week, we saw soybean aphid populations that were still relatively low. However, this week’s scouting revealed dramatic population increases in the same fields. Fields near Brookings, SD had soybean aphid populations that averaged from 50 to 200 aphids per plant.
Soybean aphid populations have continued to grow in the last couple of weeks. Although the majority of a field may have an average as low as 10-20 aphids per plant, there are definitely hot spots throughout the scouted fields.
This week we noticed large populations of redheaded flea beetles in soybean. These beetles get their name due to the distinct red-brown colored head, which is contrasted by their otherwise shiny black bodies.
While scouting soybean this week, we came across a unique caterpillar in the upper soybean canopy. At first glance, the feeding behavior of rolling leaves with silk webbing resembled that of the thistle caterpillar.
Soybean fields scouted were found to have brown spot (also called Septoria leaf spot) and frogeye leaf spot developing. However, both diseases were seen at low severity.
White mold, also known as Sclerotinia stem rot, is one of the major fungal diseases that affect soybeans. White mold has become a major concern over the last few years, especially in Eastern South Dakota.