June 27, 2008

Over the last week fields in several parts of the state have finally dried out enough that herbicide applications could be made. When the weeds are cleaned up in some fields, growers are finding poor stands. In many cases, poor stands and damping off of plants at this time have been Pythium and Phytophthora. Both of these fungal pathogens are favored by wet conditions and sometimes are referred to as water molds.

At this time in the season there are no treatments for the problem. The only action is to ensure the crop does not undergo any moisture stress if and when things dry out more. If heavy rains continue, we will see more Phytophthora in some fields. This pathogen can kill plants at any stage of development. Pythium, on the other hand, typically does not kill plants much past the V5 growth stage.

For future years, the best option is a good seed treatment. To ensure you get the correct seed treatment for your field, identify and note which pathogen(s) is present this year.

Phytophtora-infected soybeans typically have have dark stems associated with the dying plants. The dark stem will extend form the soil line up into the plant canopy.

Pythium-infected soybeans usually will have roots where the outer tissues are brown and scrape off easily. Typically, the center of the root will be intact.

Once identified, keep notes on what is affecting the field so that you can position the correct seed treatment.

In addition to seed treatment, Phytophthora resistant varieties should be used in fields with a history of Phytophthora. Additional information on Phytophthora can be found on the Plant Disease Central Web Site at archive/-/asset_publisher/VHeSpfv0Agju/content/pdc.unl.edu.

Loren J. Giesler
Extension Plant Pathologist