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Strawberry fruit infected with leather rot (right).

Strawberry

Leather Rot

Pathogen: Phytophthora cactorum

(Reviewed 6/08, updated 6/08)

In this Guideline:


SYMPTOMS AND SIGNS

All stages of fruit are susceptible to leather rot. Infected fruit develop diseased areas that are brown to shades of purple in color. The decay often expands throughout the fruit, resulting in a brown, leathery berry. The external infected area becomes tough while the internal tissue is somewhat softer. The central hollow cavity of the fruit may contain the white mycelium of the pathogen, and the fruit tastes bitter.

COMMENTS ON THE DISEASE

The leather rot pathogen requires splashing rain to transport the zoospores (motile spores) to the fruit, or in very wet conditions (i.e., flooding, standing water or pools of water on beds) the zoospores can swim to the plant.

MANAGEMENT

Leather rot is not common on annual plantings of strawberries in California because it is usually controlled by preplant fumigation and plastic mulches. Cultural practices play an important role in disease prevention; soil solarization may also provide control. Plantings held for 2 or 3 years, however, could be infected by the leather rot pathogen.

Cultural Control
Ensure that fields are prepared so that they have adequate water drainage. Remove diseased fruit and use plastic mulches. Avoid overhead irrigation; use drip irrigation. Straw mulch has been effective in controlling this disease in the eastern United States.

Soil Solarization
In warmer areas of the state, solarization has been shown to be effective for the control of soilborne pathogens and weeds. Solarization is carried out after the beds are formed and can be effective if weather conditions are ideal (30-45 days of hot weather that promotes soil temperatures of at least 122°F). The effectiveness of solarization can be increased by solarizing after incorporating the residue of a cruciferous crop, in particular broccoli or mustards, into the soil or following an application of metam sodium (40 gal/acre). For more details on how to effectively solarize soil, see Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds, UC ANR Publication 21377.

Organically Acceptable Methods
Field sanitation, proper irrigation, soil solarization, and mulches are acceptable management tools in an organically certified crop.

Treatment Decisions
If drip fumigation is planned, good results have been obtained with a sequential application of chloropicrin (200 lb/acre) or 1,3-dichloropropene/chloropicrin (300 lb/acre) followed 7 days later with metam sodium (45 gal/acre) or metam potassium (37 gal/acre). During the growing season, research data from the eastern United States indicate that mefenoxam (Ridomil Gold), fosetyl-aluminum, and phosphorus acid (Fosphite) are effective in controlling this disease. Treat before the advent of splashing rains or very damp conditions.

Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
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.
 
PREPLANT FUMIGATION
A. METHYL BROMIDE*/CHLOROPICRIN* 300–400 lb 48 0
  COMMENTS: The current Critical Use List only allows use where 1,3-dichloropropene can't be used because of local township limits. Fumigants such as methyl bromide are a source of volatile organic compounds (VOCs) but are not reactive with other air contaminants that form ozone: methyl bromide depletes ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
 
B. Sequential application of:
  (Note: Fumigants such as 1,3-dichloropropene and metam products are a source of volatile organic compounds (VOCs) but minimally reactive with other air contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.)
  1,3-DICHLOROPROPENE*/CHLOROPICRIN*
  (Telone C35) 9–12 gal (shank) 5 days 0
  COMMENTS: Effective for control of nematodes, soilborne fungal pathogens, and insects. One gallon of product weighs 11.1 lb.
 
  1,3-DICHLOROPROPENE*/CHLOROPICRIN*
  (InLine) 28–33 gal (drip) 5 days 0
  COMMENTS: Effective for control of nematodes, soilborne fungal pathogens, and insects. Requires plastic mulch. Using higher rates or plastic mulch, especially virtually impermeable film (VIF), improves weed and nematode control. One gallon of product weighs 11.2 lb.
  . . . or . . .
  CHLOROPICRIN*
  (MetaPicrin) 15–30 gal (shank) 48 0
  (Tri-Clor) 15–21.85 gal (drip) 48 0
  COMMENTS: A liquid that diffuses as a gas through soil. Very effective for control of soilborne fungal pathogens and insects. Drip irrigation requires an emulsifier. For shank fumigation, using higher rates or plastic mulch, especially virtually impermeable film (VIF), improves weed control. For drip fumigation the use of VIF will improve both nematode and weed control. One gallon of Tri-Clor weighs 13.7 lb; one gallon of MetaPicrin weighs 13.8 lb.
 
  Followed 5-7 days later by:
  METAM SODIUM*
  (Vapam HL, Sectagon 42) 37.5–75 gal 48 0
  COMMENTS: Water-soluble liquid that decomposes to a gaseous fumigant (methyl isothiocyanate). Efficacy affected by soil texture, moisture, temperature, and percent organic matter. One gallon of product contains 4.26 lb of metam sodium.
  . . . or . . .
  METAM POTASSIUM*
  (K-Pam HL) 30–60 gal 48 0
  COMMENTS: Water-soluble liquid that decomposes to a gaseous fumigant (methyl isothiocyanate). Efficacy affected by soil texture, moisture, temperature, and percent organic matter. One gallon of product contains 5.8 lb of metam potassium.
 
GROWING SEASON
A. FOSETYL-ALUMINUM
  (Aliette WDG) Label rates 12 5
  MODE OF ACTION GROUP NAME (NUMBER1): Phosphonate (33)
 
B. MEFENOXAM
  (Ridomil Gold EC) Label rates 48 30
  MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)
 
C. PHOSPHOROUS ACID
  (Fosphite) 1–2 qt 4 0
  MODE OF ACTION GROUP NAME (NUMBER1): Phosphonate (33)
  COMMENTS: Do not apply with copper-based fungicides or fertilizers; allow 20 days after or 10 days before a copper treatment.
 
** Rates are per treated acre; for bed applications, the rate per acre may be lower.
+ 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.
* Permit required from county agricultural commissioner for purchase or use.
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 County
G. T. Browne, USDA Crops Pathology and Genetics, UC Davis
T. R. Gordon, Plant Pathology, UC Davis
Acknowledgment for contributions to Diseases:
W. D. Gubler, Plant Pathology, UC Davis

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