Variety selection is an important factor in preventing disease buildup in the soil and in managing the negative impacts of most diseases today.
Erwinia
Description
Although bacterial disease on sugar beet is common, most of the bacteria cause little damage. The exception to the rule is the destructive bacteria Erwinia carotovora or soft rot. Several strains of the bacterium cause this damage. They enter the plant through an injury and invade the vascular vessels of the root and the petioles. Erwinia soft rot can cause serious damage. Disease potential is greatest when temperatures are in the range of 77° to 86°F (25° to 30°C).
Symptoms
Affected plants are difficult to detect until the rot is well advanced. The vascular tissues of the attacked roots are necrotic or discolored (image 1) and a pink to red-brown rot develops around them which can affect th entire root (image 2). Brown lesions can also appear on the petioles. Affected roots may become hollow without dying (image 3). As the disease progresses, plants wilt. Occasionally brown, oozing lesions occur on petioles and crown.
 Image 1 |
 Image 2 |
 Image 3 |
Development
The causal agent of the disease is a bacteria named erwinia carotovora subspecies betavasculorum. The bacteria is single celled, rod-shaped and gram-negative. Isolated colonies of the bacteria are white with a yellow to orange center and undulating to coralloid margins, resembling a fried egg.
Spread
The primary host is the sugar beet. It can overwinter on unharvested beets,
and can be detected in soil up to two months after harvest. It has also been
isolated on weeds. It is thought that the disease is spread by infected soil
deposited in plant crowns by farm machinery, splashing water and insects.
Control
The most effective way to control Erwinia is by using resistant seed varieties. Beet varieties vary widely in their resistance or susceptibility to this pathogen. Commercial varieties in California are tested for soft rot resistance; whenever possible, use resistant varieties. Follow cultural practices that promote good soil structure. Avoid throwing soil and plant debris into beet crowns during cultivation, and adjust implements to minimize injury to crown and tops. Additionally, the judicious use of nitrogen is recommended.
