Soybean Phytophthora 7-9-15

Soybean Phytophthora 7-9-15

Conditions Favorable for Early to Mid Season Soybean Diseases

July 9, 2015

With consistent moisture in many parts of the state, we continue to see some fields developing disease problems. Fields vary significantly in growth stage with most in the later vegetative stages with flowering close to full bloom in some.

Nebraska Extension Plant Pathologist Loren Giesler discusses why we're seeing phytophthora in wet Nebraska fields and what to look for.
The main water-favored disease present in warmer soils is Phytophthora which is showing up in several fields. If moisture and warmer temperatures continue, we expect to see more Phytophthora in fields with a history of this disease. At this time in the season there are no treatments for phytophthora. The only action is to ensure the crop does not undergo any moisture stress if and when conditions become drier.

Pythium also may be evident in some fields. Phytophthora can kill plants at any stage of development, but Pythium typically does not kill plants much past the V5 growth stage. If your stands are good and past that stage, you should not have to worry about Pythium. 

I encourage you to get a diagnosis of what the problem is in your fields so that proper management actions can be taken in the future. Based on field history, management actions would include seed treatment and use of resistant varieties (for Phytophthora). In fields where a seed treatment fungicide was used and seedling disease is still developing (in late replant situations), this may be due to the wrong treatment or excessive moisture leading to product failure under extreme conditions.  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.  

Resources

More information on product rates and management for Phytophthora can be found in "Management of Phytophthora Root and Stem Rot of Soybeans" (NebGuide G1785).  Also check the Soybean section in the Plant Diseases area of CropWatch for further information and videos.

Loren Giesler
Extension Plant Pathologist