profile7

Disease Profile 7
Rhizoctonia Root and Crown Rot

Sugarbeet Image Courtesy of:
http://www.uidaho.edu/sugarbeet/disease/rtdspnw.htm

Last updated by
Nick Dolezal
on March 27th, 2002

Common Names of Rhizoctonia Root and Crown Rot:

    -Root Rot
    -Sugarbeet Root Rot
    -Rhizoctonia

Causal Agent:

Species:
Rhizoctonia solani
(There are 9 different strains of this fungus which affect plants each in little different way!)

Class:
Fungi

Host Range:

Here are some of the alternate crops, ornamentals, and weeds that Rhizoctonia can survive on:

Field Crops	Ornamentals	Weeds
Sugarbeets	none found	none found
Potatoes
Alfalfa
Beans

Geographical Range:

Root rot can be found throughout the corn belt of the United States and wherever sugarbeets are grown.

Symptoms:

As seen on the photo at the top of this page, root rot can significantly reduce sugarbeet tonnage by preventing good root development. Seedlings may be affected by the occurrence of damping off as the fungus gets takes hold in plant roots. Generally, wilting of plant foliage is the first noticeable system. This sign usually occurs on the oldest leaves on the infected sugarbeet. As much as 20-50% loss may occur from this fungus. If a plant is dug up, deep cankers or black cracks can be observed. Eventually the whole beet may become black in color. In severe cases of root rot, the sugarbeet may be literally hollowed out and rotted away.

Dissemination:

The plant pathogen is generally carried to new areas by the movement of soil. However, Rhizoctonia can also be introduced into a new field by the transport of infected plant material carried on farm equipment.

Disease Cycle:

Rhizoctonia solani lives in the soil in the form of mycelium or sclerotia. When soil is moist, warm, and poor in structure (as often beet ground is) the pathogen will flourish if primary inoculum is present. However, Rhizoctonia levels can drop rapidly if the soil becomes too wet or too warm. As a general rule, Rhizoctonia attacks the crown of a sugarbeet plant and may do so at any point during the growing season. However, the fungus can infect any part of the plant root. This fungus is a facultative parasite so it can survive on living plant material or on dead material. Not much more could be found on the disease cycle.

Control Measures:

Once Rhizoctonia has a foothold in a soil it is difficult to reduce inoculum amounts in the soil. There are no chemical that can be legally used for this pathogen on sugarbeets either. To ensure that mycelium and sclerotia doesn't develop to infect crop roots, one must promote good plant health in the field. A farmer can do this by ensuring that plants have plenty of nutrients available and limit the onset of any other pests. Also, due to the fact that the pathogen enters for the most part through the crown, a farmer can limit how much he hills the soil around the plant. Hilling is a common practice among sugarbeet growers. Soil inoculum can build up quickly if the crop rotation is such that the pathogen can survive over the span of the rotation. Wheat or corn are the best rotational options while soybeans and potatoes are not as they are alternate hosts. The longer a farmer can stay away from host crops in their rotation the better so as to reduce inoculum levels. Some resistant varieties are available for farmers with serious problems and rotational restrictions. Also, as the recent research summary states, there are seed treatments available for sugarbeet seed which inhibits damping off in seedling development.

Recent Research-Summary: