Hilleshög -

Cercospora Leaf Spot

Identification

Cercospora leaf spot is caused by a fungus

Detection

Symptoms typically first appear on older leaves before progressing to younger leaves
Symptoms may occur in as few as five days after infection (10 - 14 day infection cycle)
Lesions are circular (about 1/8 inch in diameter) with ash gray centers containing black dots (which are the spores). The border of the lesion is a reddish/purple.
In severe cases, spots may grow together to kill entire leaf
Under ideal conditions, more spores are produced every 5 days

Cause of Infection

Primary infections occur from germination of spores in infected beet debris, which spread by wind, water and occasionally insects.
Daytime temperatures of 80° to 90° and nighttime temperatures above 60° in conjunction with 90-100% relative humidity favor disease development
Spores will not form in temperatures below 50° F

Cause of Damage

Cercospora lesions are a form of defoliation
Under normal conditions, sugarbeets draw energy from their leaves to produce sugar in their roots
Defoliation diminishes a beet's ability to complete this process and produce sugar and root yield
As leaves are defoliated, the beet cannot produce sugar
As leaves are defoliated, the beet uses stored sugar to grow new leaves, rather than growing a larger root or storing additional sugar
Severely diseased leaves wither and die, resulting in full leaf defoliation

Beet Damage

Control

Crop rotation - three years or longer
Plant beets at least 100 yards from a field infected last year
Good control is needed in adjacent fields to reduce infection in subsequent years crops
Plowing beet refuse helps reduce inoculum’s survival and dispersal
Variety resistance
Use disease management software, such as beetcast, to optimize fungicide applications
Fungicides - two types: protectant and systemic (Fungicides should be rotated to avoid fungal resistance)