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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Lesions grow together as common leaf spot develops.

Strawberry

Common Leaf Spot

Pathogen: Ramularia tulasneii

(Reviewed 6/08, updated 6/08)

In this Guideline:

SYMPTOMS

Common leaf spot first appears as small, deep purple spots on the upper surface of leaves. Spots enlarge to 0.125 to 0.25 inch (3-6 mm) in diameter with the center portion of the lesion turning brown then gray to white, depending on the age of the leaf and environmental conditions. Numerous spots may coalesce to kill the leaf.

On petioles, stolons, calyxes, and fruit trusses, elongated lesions may form and interfere with water transport in the plant, weaken the structure, or allow invasion by secondary organisms.

COMMENTS ON THE DISEASE

Common leaf spot is the most important of the strawberry leaf spot diseases in California. The pathogen is introduced into fruit production fields as small, black sclerotia on infected nursery material. Germination of sclerotia is initiated by fall and winter rains or sprinkler irrigation. Spores are dispersed by wind-driven rain.

MANAGEMENT

Taking steps to reduce inoculum on planting stock greatly reduces the likelihood of disease development. The only treatment that has been shown to work in California is the use of chlorothalonil in the nursery; this treatment will almost completely eliminate the disease in fruit production fields.

Cultural Control
Use resistant cultivars and drip irrigation, remove infected leaves when practical, and be sure planting stock is clean. Choose a growing area with environmental conditions that are not conducive to disease development.

Organically Acceptable Methods
Cultural controls, including soil solarization, are acceptable for use on an organically certified crop.

Treatment Decisions
To reduce the likelihood of resistance building up, use fungicides only when monitoring indicates they are necessary.

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. Also consider the general properties of the fungicide as well as information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. CHLOROTHALONIL
  (BravoWeatherStik) 1.5 pt 12 N.A.
  MODE OF ACTION GROUP NAME (NUMBER1): Chloronitrile (M5)
  COMMENTS: Use allowed under a Section 24 (c) Special Local Needs registration. May be used in nonbearing nurseries and as a preplant dip of transplants. Apply in nursery before disease establishment.
 
B. MYCLOBUTANIL
  (Rally) 40W 2.5–5 oz 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Apply in a minimum of 50 gal water/acre. Do not apply more than 30 oz/acre/year.
 
C. TRIFLUMIZOLE
  (Procure) 50WS 4–8 oz 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
N.A. Not applicable.
** Apply all materials in 200 gal water/acre to ensure adequate coverage.
+ 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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468
Diseases
S. T. Koike, UC Cooperative Extension, Monterey Co.
W. D. Gubler, Plant Pathology, UC Davis
G. T. Browne, USDA Crops Pathology and Genetics, UC Davis

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