How to Manage Pests

UC Pest Management Guidelines

Strawberry

Red Stele

Pathogen: Phytophthora fragariae var. fragariae

(Reviewed 6/08, updated 6/08)

In this Guideline:


SYMPTOMS AND SIGNS

Symptoms of red stele include severe stunting, occasionally followed by death of plants. Symptoms first appear on plants located in low, poorly drained parts of the field. Affected plants become stunted as older leaves die and are replaced by smaller, younger leaves with short petioles. Young lateral roots are often completely rotted. New crown roots die from their tips back, producing a symptom called "rat tail." Splitting affected roots reveals the red stele symptom (red coloration in the core of the root above the rotted end) from which the disease gets its name.

COMMENTS ON THE DISEASE

Most infections are limited to winter and early spring in California. Optimum conditions for disease development occur when the soil is saturated and temperatures are cool. Under these conditions the pathogen produces zoospores (motile spores) that swim to the roots and infect them. Well-drained soil can minimize disease incidence and severity.

MANAGEMENT

Disease incidence and severity can be minimized by locating strawberry fields on well-drained soil, planting annually with certified transplants, fumigating the soil before planting, and using raised beds to provide optimum drainage. The use of systemic fungicides may be helpful. Avoid excessive or insufficient amounts of irrigation water. There are no commercially available California strawberry cultivars with resistance to the pathogen that causes red stele.

Cultural Control
Use raised beds and carefully managed drip irrigation; plant in noninfested soils that have good drainage. Also, use clean plant stock and consult your farm advisor about cultivar susceptibility. Soil solarization can also provide control.

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
Control red stele in an organically certified crop with cultural controls.

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). Preplant dips and foliar sprays with fosetyl-aluminum or postplant ground or drip applications of mefenoxam are advisable when field history or environmental conditions suggest significant disease risk.

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.
  . . . or . . .
  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.
 
DURING AND AFTER PLANTING
A. PHOSPHORUS 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.
 
B. FOSETYL-ALUMINUM 2.5 lb/100 gal for plant dips 12 0
  (Aliette WDG ) or
    2.5–5 lb/acre for postplant foliar sprays 12 5
  MODE OF ACTION GROUP NAME (NUMBER1): Phosphonate (33)
  COMMENTS: May be applied as a preplant dip and as a foliar spray, beginning 14 to 21 days after planting and continuing at 30- to 60-day intervals as long as conditions favor disease development. See manufacturer precautions on product label regarding copper, buffering, adjuvants, and surfactants.
 
C. MEFENOXAM
  (Ridomil Gold EC) 1 pt 48 0
  MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)
  COMMENTS: May be applied with ground application equipment or through drip irrigation systems. In fruit production fields, apply just after planting; up to two additional applications may be made according to label guidelines. Do not apply more than 1.5 qt/acre/year.
 
** 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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