Symptoms and Signs
Small yellow spots, visible on both sides of the leaf, are the first symptom of early blight. Later the spots grow into gray, circular lesions that may be 0.25 to 0.75 inch in diameter. As leaf spots dry out, the tissue becomes papery in texture and often splits and cracks. Elongated lesions may develop on petioles. Under favorable conditions (temperatures between 60° and 86°F), the lesions will coalesce and cause a blighting effect on the leaves. The gray, fuzzy growth of the fungus may be observed in the centers of leaf and petiole lesions, but distinct structures (such as those found for celery late blight) are not formed by this pathogen. Even though the fungus growth is similar, do not confuse this disease with the early blight disease that occurs on tomato and potato, which is caused by an Alternaria sp. that does not infect celery.
Comments on the Disease
Early blight is not as common as late blight in California celery. Cercospora apii is a seedborne pathogen and may also survive in the field on celery debris. Spores are spread via wind and splashing water. Celeriac is also a host of this pathogen.
Management
Cultural Control
Use Cercospora-indexed seed. Do not plant transplants infected with Cercospora apii.
Organically Acceptable Methods
Cultural controls and some copper sprays are acceptable for use on organically grown produce.
Treatment Decisions
Chemical treatments are usually not needed, but if they are, the same fungicides that control late blight will also help suppress this disease.
| Common name | Amount to use | 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. | PROPICONAZOLE | |||
| (Tilt) | 4 fl oz | 24 | 14 | |
| MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) | ||||
| COMMENTS: Apply on a 7-day schedule but do not exceed 16 fl oz of product/crop. Ground or aerial application. | ||||
| B. | AZOXYSTROBIN | |||
| (Quadris) | 9.2-15.4 fl oz | 4 | 0 | |
| MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| COMMENTS: Alternate applications with a fungicide that has a different mode of action. Do not apply more than 2.88 qt/acre/season. | ||||
| C. | TRIFLOXYSTROBIN | |||
| (Flint) | 2–3 oz | 12 | 7 | |
| MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| COMMENTS: Do not apply more than 12 oz/acre/season or more than 4 applications of strobilurin fungicides/season. Use allowed under a supplemental label. | ||||
| D. | CHLOROTHALONIL | |||
| (Bravo Ultrex) 82.5% | 1.8–2.7 lb/acre | 12 | 7 | |
| (Echo 720) 54% | 2–3 pt/acre | |||
| MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5) | ||||
| COMMENTS: Do not apply more than 18 lb a.i./acre/season. | ||||
| E. | COPPER HYDROXIDE | Label rates | ||
| (Kocide 101) | 2 lb | 24 | 0 | |
| (Champ) | 1.33 pt | 24 | 0 | |
| MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1) | ||||
| ‡ | 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 different group numbers are suitable to alternate in a resistance management program. In California, make no more than one application of a fungicide with a mode-of-action group number associated with high resistance risk before rotating to a fungicide with a different mode-of-action group number; for other fungicides, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number. |