Symptoms and Signs
Septoria petroselini only affects parsley. Typical early symptoms are small, sunken, somewhat angular tan to brown spots. The leaf spots may be surrounded with defined red-brown margins. As the disease progresses the centers of the spots become gray-brown and tiny black fungal fruiting bodies (pycnidia) may be visible on the surface of lesions. Lesions may develop on petioles.
Comments on the Disease
Septoria leaf spot is initiated via infested seed. Spores may survive and remain infectious on dead or dried leaf material for several years. Volunteer, overwintered plants and cross-infection between neighboring crops are also potential sources of infection.
Spread occurs under wet conditions (wind-driven rain, dew drips, overhead irrigation) and byequipment or people moving through wet plants. Mild temperatures and high humidity are conducive to disease.
Management
Cultural Control
- Use quality, clean, pathogen free seed or seed that has been treated to reduce seedborne diseases.
- Cultivars may vary in susceptibility; select the cultivars with known resistance to Septoria leaf spot.
- Where the disease has recently occurred rotate to nonhost crops to reduce inoculum levels in soil or infected debris. Four-year rotations are recommended for diseased fields; 2 to 3 years for nondiseased fields.
- Incorporate crop debris into the soil to speed up decomposition.
- A change from sprinkler to furrow or drip irrigation to minimize leaf wetness will reduce the spread of this disease.
- The movement of equipment or workers through severely affected fields while the canopy is wet should be avoided.
Hot water seed treatment (122°F for 25 minutes) will significantly reduce seedborne inoculum, but may reduce seed germination.
Organically Acceptable Methods
Use cultural controls and products like potassium bicarbonate (Kaligreen) in an organically certified crop.
Treatment Decisions
Use strobilurin fungicides like azoxystrobin (Azoxystar) to control this disease.
Use pathogen-free seeds or treat seeds with fungicide prior to planting.
| 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. | AZOXYSTROBIN | |||
| (Azoxystar) | 6.0–15.5 fl oz | 4 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): 11 | ||||
| COMMENTS: Apply in 7- to 14-day intervals. May be applied the day of harvest. | ||||
| B. | PENTHIOPYRAD | |||
| (Fontelis) | 14–24 fl oz | 12 | 3 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): 7 | ||||
| COMMENTS: Registered on parsley, not on cilantro.. Apply in 7- to 14-day intervals. Do not make more than two sequential applications before alternating to a labeled fungicide with a different mode of action (non-Group 7). | ||||
| C. | POTASSIUM BICARBONATE | |||
| (Kaligreen)# | 2.5–3 lb | 4 | 1 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): An inorganic salt | ||||
| COMMENTS: Research is lacking for use of this product in parsley. | ||||
| ‡ | 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. |
| # | Acceptable for use on organically grown produce. |
| 1 | Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group number are suitable to alternate in a resistance management program. For fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17, make no more than one application 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 fungicide with a different mode-of-action group number. |