How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

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 beet 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.

MANAGEMENT

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.

Common name		Amount/Acre**	P.H.I.+
(trade name)			(days)
A.	SULFUR#
	(Dust)	30 lb	0
	(Micronized wettable)	10 lb
	MODE OF ACTION: A multi-site contact (Group M)1 inorganic fungicide.
	COMMENTS: Other types of sulfurs may be used.
B.	PYRACLOSTROBIN
	(Headline)	9-12 fl oz	7
	MODE OF ACTION: A Qol (Group 11)1 fungicide.
	COMMENTS: Maximum use per year is 48 oz/acre, but do not reapply. Alternate use with other mode of action fungicides to avoid the rapid development of resistance by the disease organism.
C.	AZOXYSTROBIN
	(Quadris)	9.2-15.4 fl oz
	MODE OF ACTION: A Qol (Group 11)1 fungicide.
**	Apply in 30-60 gal of water/acre.
+	Preharvest interval. Do not apply within this many days of harvest.
#	Acceptable for use on organically grown produce.
1	Group designations are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group designation are suitable to alternate in a resistance management program. For more information, see http://www.frac.info/.

PUBLICATION

UC IPM Pest Management Guidelines: Sugarbeet
UC ANR Publication 3469
Diseases
S. Kaffka, Agronomy and Range Science, UC Davis
R. T. Lewellen, USDA, Salinas
C. A. Frate, UC Cooperative Extension, Tulare Co.
T. A. Turini, UC Cooperative Extension, Imperial Co.

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