How to Manage Pests
UC Pest Management Guidelines
Cercospora Leaf Spot
Pathogen: Cercospora beticola
(Reviewed 11/05, updated 1/10)
In this Guideline:
SYMPTOMS AND SIGNS
Symptoms of Cercospora leaf spot first appear as individual, circular spots that are tan to light brown with reddish purple borders. As the disease progresses, individual spots coalesce. Heavily infected leaves first become yellow and eventually turn brown and necrotic. Blighted leaves soon collapse and fall to the ground, but remain attached to the crown. Heart leaves are usually less severely affected and remain green.
COMMENTS ON THE DISEASE
This disease was primarily a problem on sugarbeets grown in the southeastern portion of the San Joaquin Valley and is not common in the Imperial Valley.
Warm nights combine with high humidity in irrigated fields to provide an ideal environment for disease development. Optimum daytime temperatures for disease development are 77° to 95°F (25°–35°C) with night temperatures above 61°F (16°C) and a relative humidity of 90 to 95%. The primary source of inoculum is residue from a previously infected crop, but the fungus can be carried on seed and is also hosted by numerous weeds. Spores produced by the fungus are dispersed by splashing rain and may also be carried by wind to susceptible sugarbeet leaves.
This disease is not generally a problem in the Imperial Valley and is not normally treated for there. Varieties vary considerably in resistance, with the highest-yielding current varieties having the least resistance. Growers planting sugarbeets in late fall or early spring for an early fall harvest are most likely to be affected by Cercospora and should use a more resistant variety if possible.
To effectively eliminate inoculum from a field, plant sugarbeets in a 3-year rotation with nonhosts and plow to incorporate crop residues. Avoid planting a new sugarbeet field adjacent to fields planted to beets the previous season. When sprinkler irrigation is used, run sets so that windblown mist does not keep leaves wet for longer than 24 hours.
UC IPM Pest Management Guidelines:
S. Kaffka, Plant Sciences, UC Davis
Acknowledgement for contributions to Diseases:R. T. Lewellen, USDA, Salinas
C. A. Frate, UC Cooperative Extension, Tulare County