Pythium Root Rot

Jesse Fulbright, MSU Liberty County Extension

There have been various reports recently, on a local and a statewide level, of some yellowing in winter wheat.  While this is nothing that is out of the ordinary for our springs, I wanted to address one possible cause of the yellowing this week.

Pythium root rot has been confirmed on winter wheat in counties near us.  Pythium is favored by very wet conditions and cool soils.  It usually infects plants in the spring and is caused by a water mold pathogen that produces spores that move in soil water. 

Symptoms include black mushy roots, a lack of fine root hairs, a constriction at the soil line, and roots that can be ‘stripped’ off the center vascular tissue.  These symptoms can be difficult to diagnose if the plant is simply pulled out of the ground.  For this reason, I would encourage anyone worried about their yellowing wheat to dig a sample out of the ground so that a more accurate diagnosis can be made.  As mentioned, fields will be a yellow color, like a nutrient deficiency, and have patches in low‐lying areas or where water flows that have more severe symptoms associated with reduced root mass. 

Characteristic circular pattern of root rot at the tillering stage - in this case, a combination of
 Pythium and  Rhizoctonia. Photo courtesy of Mary Burrows.

 

Pythium is common in Montana soils and survives for years as a structure called an oospore.  Crop rotation is not effective as the pathogen will infect most crops.  Many of the cases that have been seen this spring have also been associated with environmental stress including extended snow cover, freeze/thaw cycles with excessive water, and nutrient deficiency.  

Infection of plants by Pythium can be managed by applications of metalaxyl or mefenoxam at planting.  Since seed treatments last approximately 2 weeks, fall planted and perennial crops are susceptible at this time.  Most of the wheat in the diagnostic lab has low levels of Pythium and the overall root system is healthy.  Plants should recover and seed treatments should be used on future crops.

If you have questions about your crop, or see it yellowing please give contact your local county Extension office.  There are also over small grain root and crown diseases that might be affecting our crops.  For further information, there is also a MontGuide titled, “Small Grain Root and Crown Diseases” that is able to be downloaded from www.msuextension.org or picked up at your local county Extension office.