Symptoms and Signs
Common leaf spot first appears as small, deep purple spots on the upper surface of leaves. Spots enlarge to 0.125 to 0.25 inch (3–6 mm) in diameter with the center portion of the lesion turning brown then gray to white, depending on the age of the leaf and environmental conditions. Numerous spots may coalesce to kill the leaf.
On petioles, stolons, calyxes, and fruit trusses, elongated lesions may form and interfere with water transport in the plant, weaken the structure, or allow invasion by secondary organisms.
Comments on the Disease
Common leaf spot is one of the more important fungal leaf spot diseases of strawberry in California and is extremely common in areas with high rainfall. The pathogen is introduced into fruit production fields as small, black sclerotia on infected nursery material. Germination of sclerotia is initiated by fall and winter rains or sprinkler irrigation. Spores are dispersed by wind-driven rain.
Management
Reducing inoculum on planting stock greatly reduces the likelihood of disease development.
Cultural Control
Use drip irrigation, remove infected leaves when practical, and be sure planting stock is clean. Choose a growing area with environmental conditions that are not conducive to disease development.
Organically Acceptable Methods
Cultural controls are acceptable for use on an organically certified crop.
Treatment Decisions
Common leaf spot is a relatively minor disease on production strawberries in California; use fungicides only when monitoring indicates they are necessary.
| 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. | ||||
| A. | CHLOROTHALONIL | |||
| (Bravo Weather Stik) | 1.5 pt | 12 | NA | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M5) | ||||
| COMMENTS: May be used in nonbearing nurseries and as a preplant dip of transplants. Apply in nursery before disease establishment. | ||||
| B. | MYCLOBUTANIL | |||
| (Rally 40W) | 2.5–5 oz | 24 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) | ||||
| COMMENTS: Apply in a minimum of 50 gal water/acre. Do not apply more than 30 oz/acre per year. | ||||
| ** | Apply all pesticides in 200 gal water/acre to ensure adequate coverage. |
| ‡ | 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. |
| 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. |
| NA | Not applicable. |