How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS AND SIGNS

Botrytis blossom and shoot blight occurs in early spring and fruit blight later in spring. The first symptom to be observed is wilting of tender shoots; later leaves shrivel and dry. Young shoots die and the leaves remain attached, a symptom called flagging.

Blossom blight is more severe in male than female trees, especially in the 02-16 and 02-18 male selections. The fungus enters the flower and invades the wood where it causes cankers on current or two-year-old shoots. Cankers can coalesce and measure up to 10 inches (25 cm) long. When cool, wet weather prevails, diseased blossoms and basal portions of shoots are generally covered by buff-colored massed of spores. Large circular lesions can develop on blades of both female and male trees, and portions of the leaf blade (usually a V-shaped area near the terminal) mainly on male trees may also be infected and killed by the fungus. Late rains can result in infections of fruit clusters, killing parts or the entire cluster, which become beige in color.

COMMENTS ON THE DISEASE

Infections occur in spring on succulent current-season growth. Most Botrytis cankers occur at the base of shoots and most likely start from contaminated buds and bud scales. The fungus colonizes the bud scales and then grows and infects the developing shoot. Shoots wilt and form a shepherd's crook. Inflorescences, especially in male trees, are also attacked.

Blighted shoots provide inoculum during the current growing season and in the following spring. Under humid conditions, the fungus colonizes and sporulates on male flowers that are on the tree or already dropped to the ground. Other sources of inoculum include infected weeds, leaves, and immature fruit dropped to the ground, or other crops neighboring the pistachio orchard. The disease is prevalent during cool, wet springs and causes damage by killing current season shoots and fruit, thus reducing fruiting wood for the following season and yields (fruit blight phase).

MANAGEMENT

Orchard sanitation may help reduce the incidence of Botrytis blight. By pruning blighted shoots and removing them from the orchard the level of inoculum in the orchard may be reduced. Also, by pruning the blighted shoots and shoots with cankers, the potential for invasion of the tree by Botryosphaeria dothidea is reduced.

If spring weather is cool and wet during bloom, consider treating for this disease.

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.
A.	FENHEXAMID
	(Elevate) 50 WDG	1–1.5 lb	12	—
	MODE OF ACTION GROUP NAME (NUMBER1): Hydroxyanilide (17)
	COMMENTS: Apply at 5-10% bloom and full bloom. Do not apply more than 6 lb product/acre/season.
B.	PYRACLOSTROBIN/BOSCALID
	(Pristine)	10.5–14.5 oz	12	14
	MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
	COMMENTS: Use allowed under FIFRA Section 2 (ee) permit.
C.	CYPRODINIL/FLUDIOXONIL
	(Switch) 62.5 WG	11–14 oz	12	7
	MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9) and Phenylpyrrole (12)
	COMMENTS: Make first application at early bloom and a second 14 days later. Do not apply more than 56 oz product/acre/year.
D.	PYRIMETHANIL
	(Scala) SC	18 fl oz	12	30
	MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
E.	THIOPHANATE-METHYL
	(Topsin) M WSB	1.5–2 lb	72	—
	MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
	COMMENTS: Apply at bloom. Restricted entry interval is 3 days. Do not apply more than 2 lb/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.
—	Not applicable.

PUBLICATION

UC IPM Pest Management Guidelines:
Pistachio
UC ANR Publication 3461
Diseases
T. J. Michailides, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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