How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Botrytis blossom blight starts when the pathogen attacks the calyx and flower petals, causing them to wither. As fruit starts to develop, a brown lesion forms where the diseased calyx touched the fruit surface. The lesion quickly spreads over the entire fruit, killing it while it is still very small. Grayish tufts of spores form on infected plant parts.

COMMENTS ON THE DISEASE

Decay of flower parts is a serious problem in coastal areas if not controlled. It can become a problem in other growing areas when there is prolonged wet and cool weather during bloom.

Spores form on infected, dead flower parts, fruit mummies on the orchard floor, and on other organic matter such as dead or senescent weeds. In spring, splashing rain and wind spread these spores to opening flowers. Flower parts are infected directly by germinating spores and the pathogen moves into developing fruit from infected flower parts. Green fruit rot develops when damp weather occurs while flower shucks still cling to the surface of young fruit. Cooler weather favors retention of the shucks, which are colonized by the pathogen and increases the likelihood of green fruit rot.

MANAGEMENT

Weather conditions in coastal districts usually favor Botrytis blight every season, and a fungicide application is recommended at full bloom to prevent serious losses. In other areas, treatment is necessary only when wet weather is expected during bloom.

Common name		Amount/Acre	R.E.I.+	P.H.I.+
(trade name)			(hours)	(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. Not all registered pesticides are listed. Always read label of product being used.
A.	TEBUCONAZOLE
	(Elite, Orius, etc.) 45WP	4–8 oz	12	0
	MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
B.	IPRODIONE
	(Rovral, Iprodione, Nevado)	1–2 pt	24	NA
	MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
	COMMENTS: Addition of a narrow range oil (superior, supreme) at 1–2% increases the effectiveness of this material. Do not apply after petal fall.
C.	THIOPHANATE METHYL
	(Topsin M, T-Methyl, etc.)	0.5 lb/100 gal water up to 1.5 lb/acre	12	1
	MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
	COMMENTS: Use only once a year. Resistance to thiophanate methyl is common in populations of Monilinia fructicola and Botrytis cinerea in California cherry orchards. If resistance has occurred in the orchard, do not use this product. Otherwise, use only in combination or in an alternating application program with a fungicide that has a different Group number.
D.	PYRACLOSTROBIN/BOSCALID
	(Pristine)	10.5–14.5 oz	12	0
	MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
	COMMENTS: To reduce the potential for the development of resistance, do not make more than a total of five applications/season of Group 7 or 11 fungicides.
E.	FENHEXAMID
	(Elevate) 50WDG	1–1.5 lb	12	0
	MODE OF ACTION GROUP NAME (NUMBER1): Hydroxyanilide (17)
	COMMENTS: Do not apply more than 6 lb/acre/season.
F.	CAPTAN
	(Various) 50WP	4 lb	4 days	0
	MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
	COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.
G.	CHLOROTHALONIL
	(Echo 720)	3.125–4.125 pt	12	0
	(Bravo Ultrex)	2.8–3.8 lb	12	0
	(Bravo Weather Stik)	3.125–4.125 pt	12	0
	MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
	COMMENTS: May cause an allergic skin reaction in some people. Do not use with or closely following oil sprays. Do not apply more than 20.5 pt Bravo Weather Stik/acre/season. Do not apply more than 18.8 lb Bravo Ultrex/acre/season.
+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1	Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.
NA	Not applicable.

PUBLICATION

UC IPM Pest Management Guidelines: Cherry
UC ANR Publication 3440
Diseases
J. E. Adaskaveg, Plant Pathology, UC Riverside
J. L. Caprile, UC Cooperative Extension, Contra Costa County
Acknowledgment for contributions to Diseases:
W. D. Gubler, Plant Pathology, UC Davis
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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