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 area of the fruit, if hollow, 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 to prevent soil splashing 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
Use field sanitation, good drainage, proper irrigation, soil solarization, and mulches in an organically certified crop.
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. During the growing season, research data from the eastern United States indicate that mefenoxam (Ridomil Gold), fosetyl-aluminum (Aliette), and phosphorous acid (Fosphite) are effective in controlling this disease. Treat before the advent of splashing rains or very damp conditions.
| 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 | ||||
| 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. | ||||
| Followed 5-7 days after fumigation by 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. | ||||
| C. | FOSETYL-AL | |||
| (Aliette WDG) | Label rates | 12 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Phosphonate (33) | ||||
| COMMENTS: Apply as a preplant dip to strawberry roots and crowns for 15 to 30 minutes; plant within 24 hours after dipping. | ||||
| GROWING SEASON | ||||
| A. | FOSETYL-AL | |||
| (Aliette WDG) | Label rates | 12 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Phosphonate (33) | ||||
| B. | MEFENOXAM | |||
| (Ridomil Gold SL) | Label rates | 48 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Phenylamide (4) | ||||
| C. | 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. | ||||
| ** | 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. |