How to Manage Pests

UC Pest Management Guidelines

Strawberry

Phytophthora Crown Rot

Pathogens: Phytophthora cactorum, P. citricola, P. parasitica, and P. megasperma

(Reviewed 6/08, updated 6/08)

In this Guideline:


SYMPTOMS AND SIGNS

Initially, symptoms typically include plant stunting and small leaves. As the season progresses, plant collapse may occur rapidly or slowly. When infected plants are cut open, a brown discoloration can be seen in the crown vascular tissue or throughout the crown tissue. The same Phytophthora species also attack roots, causing a brown to black root rot.

COMMENTS ON THE DISEASES

Of the Phytophthora species involved, P. cactorum is the most common; the others are much less prevalent on strawberry. Phytophthora is soilborne. When the soil becomes saturated with water, the pathogen can produce and release zoospores, which swim through water-filled pores to infect plant tissue. Phytophthora species also produce resilient spores (chlamydospores, oospores) that enable them to survive in soil for long periods without a host or under adverse conditions. Infections can occur during cool to moderate temperatures, which are typical throughout coastal fruit-production cycles.

MANAGEMENT

Soil fumigation and good cultural practices provide adequate control of Phytophthora in production fields. Good cultural practices include the use of certified transplants, avoiding poorly drained soils, and preparing fields to provide good soil drainage during wet weather. Phytophthora can be moved in water that has drained from infested fields, so avoid using runoff water for irrigation or for wetting down field roads for dust control. In fields that are prone to Phytophthora problems, you may want to plant less susceptible cultivars. Even with tolerant cultivars, however, it is important to follow good cultural practices.

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
Good cultural practices such as using resistant or tolerant varieties and careful water and soil management (improving soil drainage; raised beds) can be used to manage Phytophthora crown rot 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). Preplant dips and foliar sprays with fosetyl-aluminum or postplant ground or drip applications of mefenoxam are advisable when Phytophthora-susceptible cultivars are used or 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 Critical Use List for 2007 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.
 
C. 1,3–DICHLOROPROPENE*/CHLOROPICRIN*
  (Telone C35) 425 lb 5 days 0
 
D. CHLOROPICRIN* 300 lb 48 0
 
DURING AND AFTER PLANTING
A. 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.
 
B. FOSETYL-ALUMINUM 2.5 lb/100 gal for plant dips 12 0
    or
  (Aliette WDG) 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 14–21 days after planting and continuing at 30- to 60-day intervals when conditions favor disease development. See manufacturer precautions on product label regarding copper, buffering, adjuvants, and surfactants.
 
C. MEFENOXAM
  (Ridomil Gold EC) 1 pt 48 30
  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 2 additional applications may be made according to label guidelines. Do not use 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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