How to Manage Pests
UC Pest Management Guidelines
Pathogen: Erysiphe polygoni
(Reviewed 11/05, updated 1/10, pesticides updated 9/16)
In this Guideline:
SYMPTOMS AND SIGNS
The first signs of powdery mildew are small, white powdery spots that appear usually on the under surface of older leaves when sugarbeet plants are 2 to 6 months old. Under suitable conditions, the fungus spreads rapidly over the entire surface of the leaf, and eventually to all leaves on affected plants. Older leaves may yellow and eventually become necrotic and die.
COMMENTS ON THE DISEASE
Powdery mildew is an annual problem on sugarbeet in California. The fungus overwinters on sugarbeet and other Beta species such as swiss chard, table beets and wild Beta species that grow throughout the winter. Ideal conditions for disease development are warm, dry weather; optimum temperatures for growth of the fungus are between 60° and 86°F (15° and 30°C). Very high daily temperatures of 100°F (38°C) or higher tend to arrest disease development. Following initial infection, the fungus grows over the surface of the leaf and produces asexual spores (conidia), which give the leaf a powdery appearance. The conidia are airborne and can be carried considerable distances to start new infections. If the disease is not controlled, 20 to 35% loss in sugar yield can occur.
Currently, varieties with moderate resistance are available. Use these varieties in combination with chemical control measures. Apply a fungicide before, if possible, or when the first small, white powdery spots appear on the undersurface of leaves. Repeated applications are necessary at 3- to 6-week intervals if the disease reappears. Good coverage of the beet leaf surfaces is essential.
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