How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Older leaves and leaf petioles of plants with powdery mildew are usually covered with a white, powdery growth. Young leaves develop small, circular, white, powdery spots that slowly enlarge to cover the leaflets. A slight chlorosis or yellowing may appear on leaves infected by the fungus.

COMMENTS ON THE DISEASE

The fungus survives on overwintered carrots and related weed hosts. The airborne spores may be carried great distances. Foliage symptoms usually do not appear until leaves are mature, and leaves can survive even with heavy infections. Fungal infection and disease development are favored by high humidity during evening and morning hours, and temperatures between 55° and 90°F.

MANAGEMENT

Cultural Control
Use tolerant cultivars and maintain good plant vigor.

Organically Acceptable Methods
Cultural control and sprays of sulfur and Bacillus subtilis are acceptable for use on organically grown produce.

Treatment Decisions
Chemical controls are not recommended, unless infections appear very early in the growing season.

Common name		Amount/Acre	P.H.I.+
(trade name)			(days)
A.	AZOXYSTROBIN
	(Quadris)	9.2–15.4 fl oz	0
	MODE OF ACTION: A Qol (Group 11)1 fungicide.
	COMMENTS: Do not make more than one application before rotating to a fungicide with a different mode of action. Do not make more than four foliar applications of strobilurin fungicides per crop.
B.	PYRACLOSTROBIN
	(Cabrio) EG	8–12 oz	0
	MODE OF ACTION: A Qol (Group 11)1 fungicide.
	COMMENTS: Do not make more than two sequential applications before rotating to a fungicide with a different mode of action. Do not make more than three applications of strobilurin fungicides per crop.
C.	TRIFLOXYSTROBIN
	(Flint)	2–3 oz	7
	MODE OF ACTION: A Qol (Group 11)1 fungicide.
	COMMENTS: To limit potential for resistance development do not apply more than 3 sequential applications or a total of 4 applications of all strobilurins per season. Do not apply more than 12 oz/acre/year.
D.	SULFUR#	3-10 lb
	...OR...
	SULFUR DUST#	Label directions
	MODE OF ACTION: A multi-site contact (Group M)1 inorganic fungicide.
	COMMENTS: Apply at first sign of disease and repeat at 14 days as needed to maintain control.
E.	BACILLUS SUBTILIS
	(Serenade MAX)#	1–3 lb	0
	(Serenade ASO)#	2–4 qt	0
	MODE OF ACTION: Unknown.
	COMMENTS: Serenade ASO has a special local needs registration for organically grown carrots. Apply Serenade MAX as a foliar spray; thorough coverage is essential. Serenade ASO is applied with chemigation equipment.
+ Preharvest interval. Do not apply within this many days of harvest. 1 Group designations are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group designation are suitable to alternate in a resistance management program. For more information, see http://www.frac.info/. # Acceptable for use on organically grown produce.

PUBLICATION

UC IPM Pest Management Guidelines: Carrot
UC ANR Publication 3438
Diseases
R. M. Davis, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara Co.
J. Nunez, UC Cooperative Extension, Kern Co.
T. A. Turini, UC Cooperative Extension, Imperial Co.
Acknowledgment for contributions to the diseases section:
B. W. Falk, Plant Pathology, UC Davis

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