Agriculture: Strawberry Pest Management Guidelines

Red Stele

Phytophthora fragariae var. fragariae

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 back from their tips, 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. Red stele can also cause a dark brown discoloration of the crown; this symptom is identical to that caused by other Phytophthora species that infect strawberry.

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 water-saturated during cool weather. 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

To minimize disease incidence and severity:

  • Locate strawberry fields on well-drained soil.
  • Plant annually with certified transplants.
  • Fumigate the soil before planting.
  • Use raised beds to provide optimum drainage.
  • Avoid excessive or insufficient amounts of irrigation water.
  • Consider using systemic fungicides.

There are no commercially available California strawberry cultivars with resistance to the pathogen that causes red stele.

Cultural Control

  • Use raised beds.
  • Carefully manage drip irrigation.
  • Plant in noninfested soils that have good drainage.
  • Use clean plant stock.
  • Consider soil solarization.

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 with cultural controls in organically certified strawberries.

Treatment Decisions

If drip fumigation is planned, good results have been obtained with a sequential application of chloropicrin or 1,3-dichloropropene plus chloropicrin followed 7 days later with metam sodium or metam potassium. 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 per acre** REI‡ PHI‡
(Example trade name)   (hours) (days)
Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
 
PREPLANT FUMIGATION
 
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.
 
A. METHYL BROMIDE*§/CHLOROPICRIN*§
  (Tri-Con 50/50) 300–400 lb See label 0
  COMMENTS: Methyl bromide use is allowed only in strawberry nurseries through the quarantine and pre-shipment (QPS) exemption. 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.
 
B. SEQUENTIAL APPLICATION
 
  First, apply one of the following
 
1,3-DICHLOROPROPENE*§/CHLOROPICRIN*§
  (Telone C35) Label rates See label 0
  (InLine) Label rates (drip) See label 0
  COMMENTS: Effective for control of nematodes, soilborne fungal pathogens, and insects. InLine requires a plastic tarp. Use higher rates or impermeable films to improve weed and nematode control. One gallon of product weighs 11.2 lb.
  . . . or . . .
CHLOROPICRIN*§
  (Tri-Clor) 150–350 lb (shank) See label 0
  (Tri-Clor EC) 200–300 lb (drip) See label 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, use higher rates or impermeable films to improve weed and nematode control. For drip fumigation the use of TIF will improve both nematode and weed control. Tri-Clor: One gallon of product weighs 13.88 lb; Tri-Clor EC: One gallon of product weighs 13.46 lb.
 
  Then, 5–7 days after fumigation apply one of the following
 
METAM SODIUM*§
  (Vapam HL, Sectagon 42) 37.5–75 gal See label 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) 30–62 gal See label 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. PHOSPHOROUS ACID
  (Fosphite) 1–3 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-AL
  (Aliette WDG) 2.5 lb/100 gal for plant dips 12 0
    . . . or . . .
    2.5–5 lb/acre for postplant foliar sprays 12 0
  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 SL) 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.
** Rates are per treated acre; for bed applications, the rate per acre may be lower.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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.
§ Do not exceed the maximum rates allowed under the California Code of Regulations Restricted Materials Use Requirements, which may be lower than maximum label rates.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. 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 a fungicide with a different mode-of-action group number.
Text Updated: 07/18
Treatment Table Updated: 07/18