How to Manage Pests

UC Pest Management Guidelines

Strawberry

Charcoal Rot

Pathogen: Macrophomina phaseolina

(Reviewed 1/13, updated 1/13)

In this Guideline:


SYMPTOMS AND SIGNS

Symptoms of charcoal rot in strawberries consist of wilting of foliage, plant stunting, and drying and death of older leaves, with the central youngest leaves often remaining green and alive. Symptoms usually first appear well after plants are established and after plants begin bearing fruit or are subjected to stress. Plants can eventually collapse and die completely. When internal tissues of plant crowns are examined, vascular and cortical tissues are dark to orange brown. Internal tissues of the main roots may also be discolored and show the same dark brown coloration.

COMMENTS ON THE DISEASE

Disease is often most severe if the infected plant is subject to stresses due to weather extremes, water stress, poor soil conditions, or heavy fruit loads. Confirmation of charcoal rot requires diagnostic procedures in a pathology lab. Note that foliar dieback and internal crown discoloration symptoms are identical to those caused by Fusarium wilt; only laboratory analysis can separate these two diseases. This soilborne fungus has a broad host range and can infect a number of other crops. The fungus persists in the soil in the form of small, black survival structures called sclerotia.

MANAGEMENT

Select locations that do not have a history of charcoal rot. Preplant fumigation, which historically has been an important component of managing Verticillium wilt in strawberry fields, will also help control Macrophomina. Fumigation will be most effective when crop residues have fully decomposed or removed. Consequently it is advisable to allow some time after incorporation before the fumigant is applied. Shank application of materials such as chloropicrin or chloropicrin/1,3 dichloropropene (Pic-Clor60) applied at high rates under retentive film can control fungal pathogens, such Fusarium and Macrophomina. Bed fumigation will not control these pathogens in the untreated furrows.

Crop rotation with broccoli has been shown to help reduce Verticillium levels in the soil; this practice may also help manage Macrophomina, although it has not yet been thoroughly researched with this disease.

Cultural Control
Strawberry cultivars

Greenhouse tests have shown that some strawberry cultivars, such as Seascape and Chandler, have some tolerance to Macrophomina, although none are completely resistant. Additional research is being conducted to develop new resistant cultivars.

Manage stress

Manage the strawberry crop so as to reduce stress on the plants. Irrigate the crop as appropriate for the stage of development, current evapotranspiration requirement, and soil moisture monitoring. Plants at the edge of the bed may be more prone to collapse due to drying or other factors associated with this location in the bed. Control pests, especially mites, which can exert significant stress on strawberry plants.

Crop Rotation

Rotating strawberries with broccoli can significantly reduce levels of the Verticillium pathogen in the soil. While not yet tested with Macrophomina, broccoli rotations may also be useful.

Organically Acceptable Methods

Select fields that do not have a history of charcoal rot. Plant tolerant cultivars. Rotate with nonsusceptible crops or with crops, such as broccoli, which have the capacity to suppress the pathogen. Avoid stressing plants.

Monitoring and 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).

Common name Amount per 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.
 
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.
 
PREPLANT FUMIGATION
A. METHYL BROMIDE* + CHLOROPICRIN* Label rates see label see label
  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
  First, apply one of the following:
 
  1. 1,3-DICHLOROPROPENE*
  (Telone II) 100-265 lb (shank) see label 0
  COMMENTS: Effective for control of nematodes, soilborne fungal pathogens, and insects. One gallon of product weighs 10.1 lb.
       . . . or . . .
  2. 1,3-DICHLOROPROPENE* + CHLOROPICRIN*
  (Telone C35) 200-400 lb (shank) see label 0
  COMMENTS: Effective for control of nematodes, soilborne fungal pathogens, and insects. One gallon of product weighs 11.2 lb.
       . . . or . . .
  3. 1,3-DICHLOROPROPENE* + CHLOROPICRIN*
  (InLine) 145-332 lb (drip) see label 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. According to state permit conditions, the maximum application rate of 1,3-dichloropropene is 332 pounds active ingredient per acre. One gallon of product weighs 11.2 lb.
       . . . or . . .
  4. CHLOROPICRIN*
  (Tri-Clor) 200-350 lb (shank) see label 0
  (Tri-Clor EC) 200-300 lb (drip) see label 0
  COMMENTS: 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. Tri-Clor: weighs 13.7 lb; Tri-Clor EC: One gallon of weighs 12.6 lb..
       . . . or . . .
  5. CHLOROPICRIN* + 1,3 DICHLOROPROPENE
  (Pic-Clor60) 300-332 lb (shank) see label 0
  (Pic-Clor60 EC) 200-300 lb see label 0
  COMMENTS: 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. According to state permit conditions, the maximum application rate of 1,3-dichloropropene is 332 pounds active ingredient per acre. Pic-Clor60: One gallon of weighs 12.1 lb; Pic-Clor60 EC: One gallon of weighs 11.8 lb.
 
  Then, 5-7 days after fumigation apply one of the following:
 
  1. 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 . . .
  2. METAM POTASSIUM*
  (K-Pam HL, Sectagon-K54) 30-45 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.
   
 C. DAZOMET*
  (Basamid) 200 lb see label 0
  COMMENTS: Powder incorporated into the soil, followed by irrigation or tarping. It decomposes to a gaseous fumigant (methyl isothiocyanate).
 
** Rates are per treated acre; for bed applications, the rate per acre may be lower.
* Permit required from county agricultural commissioner for purchase or use.
NA Not applicable.
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.

[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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