Symptoms and Signs
Initial symptoms of anthracnose are small, circular, water‑soaked lesions on both young and old leaves. Lesions later enlarge, turn brown to tan in color, and become thin and papery. In severe cases, lesions coalesce and result in severe blighting of foliage. In all cases, tiny black fruiting bodies (acervuli) form profusely in diseased tissue and are a characteristic feature of the disease. The presence of acervuli distinguishes anthracnose from Cladosporium and Stemphylium leaf spot diseases, both of which also form circular lesions.
Comments on the Disease
Anthracnose has occurred sporadically in California since first detected in the state in 1993. When the pathogen is present, spores are spread from plant‑to‑plant by splashing water from rains or sprinklers. The fungus survives in infected plant debris as dormant mycelium. However, seedborne inoculum is the most important source of initial inoculum. Infection and disease development are enhanced by very wet conditions; therefore this disease is more often seen if spring rains are common. The heavy canopy of densely planted spinach retains much moisture and particularly favors disease development on the lower leaves. Epidemics are usually more severe in fields with low fertility.
Management
Use disease-free seed. Reduce leaf moisture by avoiding sprinkler irrigation if possible. Be sure spinach fields are adequately fertilized. Resistant varieties are being developed by plant breeders. Copper fungicides have been used to slow epidemics, but they are generally ineffective, particularly under very wet conditions.
Organically Acceptable Methods
Cultural controls are acceptable for use on organically grown produce.
| 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 product being used. | ||||
| A. | COPPER HYDROXIDE | |||
| (various products) | Label rates | 24 | 0 | |
| MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1) | ||||
| COMMENTS: Copper sprays are not very effective. Apply as a protectant spray at 10–14 day intervals. Rate often depends upon disease severity. A suitable agricultural spray oil is recommended for use with some copper formulations. Consult label for specific application guidelines. | ||||
| ‡ | 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 actions. 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 fungicide with a different mode of action Group number. | |||