Symptoms and Signs
Small yellow spots, visible on both sides of the leaf, are the first symptom of early blight. Spots eventually grow into gray, circular lesions between 0.25 and 0.75 inches (6–19 mm) in diameter. As leaf spots dry out, the tissue becomes papery and often splits and cracks. Thus far for outbreaks in California, petioles have remained symptomless even if leaves have substantial spotting. Under conditions favorable to disease development (temperatures between 60° and 86°F), the lesions will coalesce and cause a blighting effect on the leaves. Gray, fuzzy growth of the fungus occurs in the centers of leaf spots, but distinct structures such as the small, dark, round reproductive bodies (pycnidia) of celery late blight fungus are not formed by this pathogen.
Even though the names are similar, do not confuse this disease with the early blight disease that occurs on tomato and potato, which is caused by an Alternaria species and does not infect celery.
Comments on the Disease
Early blight is not as common as late blight in California celery. C. 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 C. apii.
Organically Acceptable Methods
Use cultural controls in a certified organic crop.
Treatment Decisions
Fungicide applications 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 inhibitors (SBI: Class I) (3) | ||||
| B. | AZOXYSTROBIN | |||
| (Quadris) | 9.2–15.4 fl oz | 4 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| C. | TRIFLOXYSTROBIN | |||
| (Flint) | 2–3 oz | 12 | 7 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| D. | CHLOROTHALONIL | |||
| (Bravo Ultrex) | 1.4–2.7 lb | 12 | 7 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Chloronitriles (phthalonitriles) (M5) | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the 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. |