How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

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 evenually 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 can occur wherever sugarbeets are grown but is most severe in the southeastern portion of the San Joaquin Valley. In these areas, 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.

Cercospora is appearing more commonly in late summer in the southern Delta region (spring-planted, spring-harvested areas) because of the widespread use of high-yielding but susceptible varieties. It appears in the summer and may defoliate beets by early winter. Consider using a more resistant variety.

MANAGEMENT

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.

Treatment Decisions
If susceptible varieties are planted, begin treatments at the first sign of the disease. In years of severe disease outbreaks, supplemental fungicide sprays may be necessary where host resistance is inadequate or unavailable. Apply the first spray when older leaves show 10 to 20% of the leaf surface covered with spots. Further applications may be necessary on a 14-day schedule during warm, humid weather. Cercospora has evolved resistance to thiophanate methyl in the San Joaquin Valley. This fungicide should only be used tank mixed with other fungicides.

Common name		Amount/Acre**	P.H.I.+
(trade name)			(days)
A.	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 it should not be reapplied consecutively. Alternate use with other mode of action fungicides to avoid the rapid development of resistance by the disease organism.
B.	MANCOZEB
	(Penncozeb) 75DF	1.5-2 lb	14
	MODE OF ACTION: A multi-site contact (Group M)1 dithiocarbamate fungicide.
	COMMENTS: Use in tank mix combinations with thiophanate methyl for enhanced control and resistance management.
C.	THIOPHANATE METHYL
	(Topsin M) 70W	0.37-0.5 lb	21
	MODE OF ACTION: A MBC (Group 1) 1 thiophanate fungicide.
	COMMENTS: Resistant strains of the fungus have developed in the San Joaquin Valley where repeated applications of benzimidazoles (e.g., thiophanate methyl) have been used to control leaf spot. Avoid exclusive use of this material and only use it tank mixed with other fungicides. Do not apply more than 3 lb/acre/season.
D.	COPPER HYDROXIDE
	(Champ) 2F	1.33-3.33 pt
	(Kocide) 101WP	2-5 lb
	(Champion) WP	2-5 lb
	MODE OF ACTION: A multi-site contact (Group M)1 dithiocarbamate fungicide.
	COMMENTS: Apply at 10-14 day intervals; rate depends on disease severity. A suitable agricultural spray oil is recommended for use with Kocide.
**	Apply in 30-60 gal of water/acre.
+	Preharvest interval. Do not apply within this many days of harvest.
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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