How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Blossom and twig blight causes the collapse of young blossom spurs and associated leaves. A gummy exudate is present at the base of flowers. Gray-brown spore masses form on diseased flowers under high humidity.

COMMENTS ON THE DISEASE

Monilinia spp. survive on diseased twigs and mummified fruit. Its development is favored by moderate temperatures and moist-to-wet conditions during bloom or on mature fruit. The disease is not common on most plum cultivars because unlike peach and nectarine, many plums are less susceptible to brown rot blossom and twig blight, as well as fruit rot. For late-season cultivars, if an orchard has a history of the disease, or if rainfall occurs before harvest on mature fruit, protective fungicide treatments may be necessary to prevent brown rot of fruit. Late-season cultivars with harvest dates in August or September include Angeleno, Autumn Beaut, Betty Ann, Casselman, Howard Sun, and Rosemary.

MANAGEMENT

Sanitation includes removal and destruction of mummified fruit from trees and orchard floors after harvest and before bloom, as well as heavily thinned fruit from orchard floors that may be colonized by the pathogen and function as a source of inoculum during fruit maturation. On susceptible cultivars, apply a protective fungicide treatment as a delayed bloom application (20-40% full bloom). A second application may be necessary during protracted flowering or during foggy or rainy weather. Protective fungicide treatments to prevent fruit brown rot are usually not needed on early or mid-season varieties. As discussed above for late-season cultivars, if an orchard has a history of the disease, or if rainfall is forecasted on mature fruit in the harvest period, protective fungicide treatments may be necessary to prevent brown rot of fruit.

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 quality.
A.	PROPICONAZOLE
	(Orbit) 3.6EC	4 fl oz/acre
	(Bumper) 41.8EC	4 fl oz/acre
	MODE OF ACTION: A DMI (Group 3)1 triazole fungicide.
	COMMENTS: Most effective when applied before a rainfall and allowed to dry. Apply at 5–10% bloom and make a second application at 80–100% bloom. Do not apply to "Stanley" type plums.
B.	IPRODIONE
	(Rovral) 4F	1–2 lb/acre
	MODE OF ACTION: A dicarboximide (Group 2)1 fungicide.
	COMMENTS: Addition of a narrow range oil (superior, supreme) at 1–2% increases the effectiveness of this material.
C.	THIOPHANATE METHYL
	(Topsin-M) 70WP	8 oz/100 gal water
	MODE OF ACTION: A MBC (Group 1)1 thiophanate fungicide.
	COMMENTS: Strains of Monilinia fructicola resistant to thiophanate methyl have been found in California. If resistance has occurred in your orchard, do not use this fungicide. Use only 1 application of thiophanate methyl/year, and always apply with a fungicide of different chemistry.
D.	PYRACLOSTROBIN/BOSCALID
	(Pristine)	10.5–14.5 oz/acre
	MODE OF ACTION: A Qol (Group 11)1 and carboxamide (Group 7)1 fungicide.
E.	PYRIMETHANIL
	(Scala) SC	18 fl oz
	MODE OF ACTION: An AP (Group 9)1 fungicide.
F.	CYPRODINIL
	(Vangard) 75WG	5 oz
	MODE OF ACTION: An AP (Group 9)1 fungicide.
	COMMENTS: Do not apply more than 10 oz/acre/year for blossom blight control.
G.	MYCLOBUTANIL
	(Rally) 40W	2.5–6 oz
	MODE OF ACTION: A DMI (Group 3)1 triazole fungicide.
	COMMENTS: Do not apply more than 2.75 lb/acre/season.
H.	CAPTAN 50WP
	(Various)	4–6 lb
	MODE OF ACTION: A multi-site contact (Group M4)1 phthalimide fungicide.
	COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.
I.	CHLOROTHALONIL
	(Echo 720, Bravo Weather Stik)		3.125–4.125 pt/acre
	MODE OF ACTION: A multi-site contact (Group M5)1 chloronitrile fungicide.
	COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.
J.	AZOXYSTROBIN
	(Abound 2F)	12.3–15.4 fl oz
	MODE OF ACTION: A Qol (Group 11)1 fungicide.
	COMMENTS: Do not apply more than 2 applications before alternating with a fungicide that has a different mode of action.
	+  P.H.I. = Preharvest interval. Do not apply within this many days of harvest. 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 plum fungicides

• General properties
• Efficacy on plum diseases
• Treatment timing

PUBLICATION

UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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