Variety selection is an important factor in preventing disease buildup in the soil and in managing the negative impacts of most diseases today.
Rhizoctonia
Description
Rhizoctonia root rot is caused by the fungus rhizoctonia solani. This is the most common root disease of sugarbeet, occurring in most beet growing areas in the U.S. as well as throughout the world. The fungus survives in the soil as sclerotia from which mycelium grows attacking the root and causing a progressive rot leading to complete destruction of the plant.
Symptoms
Symptoms of rhizoctonia root rot are very apparent at harvest. Crown and root tissue are rotted (image 1). Surface lesions are dark brown to black. The rotted tissue often develops fissures under the crowns and will become hollow. These hollow cavities are often filled with the mycelium of the fungus. The rotted tissue due to this disease usually remains dry, unlike the rot that develops with many of the other soil fungi.
This disease, caused by a soil fungus, appears in round patches in beet fields (image 2). Affected plants wilt and the foliage slowly becomes totally necrotic. A brown rot develops on the roots, which may be partially or completely destroyed.
 Image 1 |
 Image 2 |
Development
The rhizoctonia fungus is widespread, has many crop hosts, and survives on plant debris in soil as small, resting structures called sclerotia. This disease is most common during spring and summer when conditions are warm (77° to 92°F, 25° to 33°C) and soils are moist. The fungus grows through the soil and infects the root and crown of plants. Rhizoctonia occurs in most soil types, but is most severe in heavy, poorly drained soils where water collects.
Spread
This disease is obvious at an early stage and its spread is favored by bad
soil structure and waterlogging.
Control
Growers with a history of rhizoctonia root rot should plant disease resistant varieties. One of the most important disease control practices that a grower can carry out is proper cultivation techniques. The fungus resides in the soil. If cultivation results in soil being thrown in the crowns of the beets, the fungus has a much easier time infecting the plant and causing disease. Root maggot feeding may create a entry point for rhizoctonia infection. Crop rotation is also an important aspect of disease control. Recent studies have shown that previous crops which contribute a lot of crop residue to the soil, such as wheat or sorghum, will have higher levels of disease compared to cotton, alfalfa, or sunflower as a previous crop. Some chemical control is being realized with Quadris.
