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UC Pest Management Guidelines

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Peach

Powdery Mildew

Pathogens: Sphaerotheca pannosa and Podosphaera leucotricha

(Reviewed 3/06, updated 9/06)

In this Guideline:

Symptoms
Comments on the disease
Management

SYMPTOMS

Symptoms of powdery mildew can be seen on the terminal leaves of shoots, which are covered in powdery, white fungal growth. Leaves become misshapen and puckered, and fruits develop powdery, white spots.

COMMENTS ON THE DISEASE

Sphaerotheca pannosa survives as mycelium in bud scales and as cleistothecia. Growth of the pathogen is favored by cool, moist nights and warm days. Generally, fruit is susceptible only up to time of pit hardening, but later infections can occur. Certain cultivars are more susceptible.

Occasionally the apple powdery mildew fungus, Podosphaera leucotricha, will attack peach fruit. Inoculum is produced only in apple orchards.

MANAGEMENT

Management of powdery mildew on peaches focuses on protecting fruit from infections. Watch for the disease during routine monitoring. Avoid growing peaches near apple varieties that are highly susceptible to powdery mildew, such as Jonathan, Gravenstein, and Rome Beauty. If nearby apples are expected to cause mildew problems on peaches, control the disease on apples or apply a fungicide to peaches at jacket split.

Organically Acceptable Methods

Sulfur sprays are acceptable for use in an organically certified crop.

Chemical Control

Apply one of the fungicides listed below from bloom until pit hardening when necessary. Up to three applications may be necessary in seasons when nights are cool and moist and daytime temperatures are warm. It is important to alternate materials of a different chemistry to prevent the development of resistance to a fungicide. Early treatments are the most important and most effective.

Common name			P.H.I.+
(trade name)		Amount to Use	(days)

*The following materials are listed in order of usefulness in an IPM program, taking into account efficacy. When choosing a pesticide, also consider information relating to environmental impact.*

A.	MYCLOBUTANIL
	(Rally) 40W	2.5–6 oz/acre
	MODE OF ACTION: A DMI (Group 3)¹ triazole fungicide.

B.	SULFUR DUST#	50 lb/acre
	MODE OF ACTION: A multi-site contact (Group M2)¹ inorganic fungicide.
	COMMENTS: Do not apply within 3 weeks of an oil application.

C.	WETTABLE SULFUR#	5–10 lb/100 gal water
	MODE OF ACTION: A multi-site contact (Group M2)¹ inorganic fungicide.
	COMMENTS: Do not apply within 3 weeks of an oil application.

D.	WETTABLE SULFUR#
	. . . PLUS . . .
	LIQUID LIME SULFUR#	Label rates
	MODE OF ACTION: A multi-site contact (Group M2)¹ inorganic fungicide.
	COMMENTS: Do not apply within 3 weeks of an oil application.

E.	TEBUCONAZOLE
	(Elite) 45WP	4–8 oz/acre	0
	MODE OF ACTION: A DMI (Group 3)¹ triazole fungicide.
	COMMENTS: Do not apply more than 3 lb/acre/season.

F.	PROPICONAZOLE
	(Bumper, Orbit)	4 oz/acre	0
	MODE OF ACTION: A DMI (Group 3)¹ triazole fungicide.

G.	FENBUCONAZOLE
	(Indar) 75WSP	2 oz/acre
	MODE OF ACTION: A DMI (Group 3)¹ triazole fungicide.
	COMMENTS: Do not apply more than 1 lb/acre/season.

H.	PYRACLOSTROBIN/BOSCALID
	(Pristine)	10.5–14.5 oz/acre
	MODE OF ACTION: A Qol (Group 11)¹ and carboxamide (Group 7)¹ fungicide.
	COMMENTS: To reduce the potential for resistance, do not make more than 5 applications of this or other Group 11 or 7 fungicides per season. Do not make more than 2 sequential applications of this product.

I.	THIOPHANATE METHYL
	(Topsin-M) 70WP	8 oz/100 gal water	1
	MODE OF ACTION: A MBC (Group 1)¹ thiophanate fungicide.

+	Preharvest interval. Do not apply within this many days of harvest.
#	Acceptable for use on organically grown produce.
¹	Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group number are suitable to alternate in a resistance management program. For more information, see http://www.frac.info/.

More information on peach fungicides

PUBLICATION

UC IPM Pest Management Guidelines: Peach
UC ANR Publication 3454
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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