HPIPM:Phytophtora Root Rot

Author: Ned Tisserat and Gary Franc"

Taxonomy

Domain	Eukarya
Kingdom	Chromista
Phylum	Oomycota
Class	Oomycetes
Order	Peronosporales
Family	Pythiaceae
Genus	Phytophthora

Scientific Name

Phytophthora nicotianae

Scientific Name Synonyms

Phytophthora parasitica

Phytophthora nicotianae var. parasitica

Phytophthora parasitica var. nicotianae

Phytophthora terrestris

Common Name

Phytophthora blight

Cause

Phytophthora megasperma f. sp. medicaginis

Occurrence

Phytophthora is fungus-like organism that may cause extensive mortality to young seedlings or result in a root rot of older plants. The disease is more severe in heavy soils with poor drainage.

Key Symptoms

• Damping off of seedlings
• Stunted yellow plants that may be easily pulled from soil
• Leaves may exhibit a red tinge
• Roots may be completely rotted several inches below the soil surface or have multiple rotted areas

Pathogen

This soil-borne organism persists in the soil. Infection is favored by poor drainage and heavy soils.

Biological Control

No biological control practices have been developed for bacterial leaf spot.

Cultural Control

Use resistant varieties. See the following sources for varietal information:

• University of Wisconsin forage pages http://www.uwex.edu/ces/forage/pubs/varinfo.htm
• University of Wyoming Alfalfa Disease Management Publication B1136 http://ces.uwyo.edu/PUBS/B-1136.pdf
• Avoid planting alfalfa on poorly drained soil
• Avoid late planting where soil temperatures drop below optimum for rapid germination and establishment
• Alfalfa should follow corn or small grain in a rotational sequence. Never follow alfalfa with alfalfa.
• Avoid injury to crowns and roots including cultivation and excessive traffic

Chemical Control

Seed treatments may be useful to suppress Phytophthora and Pythium seedling blights. Examples of seed treatment fungicide seed treatments for control of Phytophthora and Pythium seedling blight for alfalfa include: Apron XL (mefenoxam) Allegiance FL Allegiance LS

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.