How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Alternaria leaf spot appears as fairly large brown spots on leaves, about 0.5 to 0.75 inches (12-18 mm) in diameter. The spots turn black as the fungus produces spores. Leaf spot develops most rapidly in June and July, and trees can be almost completely defoliated by early summer when the disease is severe. The disease appears to be most severe where dews form, humidity is high, and air is stagnant.

COMMENTS ON THE DISEASE

Alternaria leaf spot can occur on almond trees grown anywhere in the Central Valley but rarely is it severe enough in the northern San Joaquin Valley to require treatment. It has been most serious on trees in the southern San Joaquin Valley and in the northern Sacramento Valley.

MANAGEMENT

The disease occurs first and is most severe on exposed leaves. Trees trained to an open and spreading canopy usually have more severe Alternaria leaf spot. Trees planted with rows in an east/west direction also have more severe disease than do orchard with rows planted north/south. Varieties that are most susceptible include Carmel, Sonora, Monterey, Winters, and Butte. Monitor for signs of the disease in April through June. If monitoring indicates the presence of Alternaria, begin late spring treatments about mid-April. In orchards with a history of the disease, treat in mid- to late April and 2 to 3 weeks later.

In some orchards, Alternaria resistance to quinone outside inhibitor fungicides (also known as strobilurins) has been documented; do not use FRAC mode of action Group number 11 fungicides in these orchards.

Common name		Amount/Acre	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a pesticide, consider the general properties of the fungicide as well as information relating to fungicide resistance and environmental impact.
A.	PYRACLOSTROBIN/BOSCALID
	(Pristine)	10.5–14.5 oz	12	25
	MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
	COMMENTS: Do not make more than 4 applications per season of strobilurins or carboxyanilides to limit the potential for the development of resistance.
B.	PYRIMETHANIL/TRIFLOXYSTROBIN
	(Distinguish)	18–26 fl oz	12	60
	MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9) and Quinone outside inhibitor (11)
	COMMENTS: Do not apply after hull split.
C.	DIFENOCONAZOLE
	(Inspire) SB	7 oz	12	30
	MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
	COMMENTS: Use allowed under a Section 18 for Butte, Glenn, Kern, and Tehama counties.
D.	IPRODIONE/NARROW RANGE OIL
	(Rovral)	Label rates	24	0
	MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
	COMMENTS: Do not use later than 5 weeks after petal fall. Not a good choice when disease pressure is severe because of label timing restrictions.
E.	AZOXYSTROBIN
	(Abound)	11–15.4 oz	4	28
	MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
	COMMENTS: Do not apply more than 2 sequential sprays before alternating with a fungicide that has a different mode of action. Do not apply more than 4 applications of strobilurin fungicides/year or apply more than 2.88 qt/product/acre/season.
F.	IPRODIONE
	(Rovral) 4F	1 pt	24	see comments
	MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
	COMMENTS: Do not use later than 5 weeks after petal fall. Do not make more than 4 applications/season. Not a good choice when disease pressure is severe because of label timing restrictions.
+	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 these two intervals is the minimum time that must elapse before harvest may occur.
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.

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
Roger Duncan, UC Cooperative Extension, Stanislaus County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center
B. A. Holtz, UC Cooperative Extension, Madera County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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