June 14, 2013

Figure 1. Damping off in soybean due to disease.   Figure 2. Phytophthora root and stem rot on soybean.

Over the last couple weeks many part of the state have received consistent and/or heavy rainfall which favors seedling diseases in soybean. This, coupled with cool temperatures, has resulted in several cases of Pythium causing poor stands and damping off of plants (Figure 1). Warmer conditions are more conducive for Phytophthora, which to date has not been identified in any samples submitted to the UNL Plant and Pest Diagnostic Lab. If moisture continues with warmer temperatures, we expect to see more Phytophthora.

Both of these fungal pathogens are favored by wet conditions, which is why we refer to them as water molds. At this point in the season there are no treatments. The only action is to ensure the crop does not undergo any moisture stress if things do dry out more. Phytophthora can kill plants at any stage of development, but Pythium typically does not kill plants much past the V5 growth stage.

I encourage you to get a diagnosis of what the problem is in your fields so proper management actions can be taken in the future. When selecting seed for next year consider seed treatments and the use of resistant varieties (for Phytophthora), based on field history.

In fields where a seed treatment fungicide was used and seedling disease is still developing, product failure under extreme conditions may be due to excessive moisture or use of the wrong treatment for the disease present. The most common example of a product rate issue is when mefenoxam or metalaxyl is put on at a rate too low for good Phytophthora control.

More information on product rates and management for Phytophthora can be found in Management of Phytophthora Root and Stem Rot of Soybeans (NebGuide G1785).

Loren Giesler
Extension Plant Pathologist