Symptoms and Signs
Two types of powdery mildew infect artichokes. Leveillula taurica is more commonly found and primarily colonizes the undersides of older leaves. Careful examination of leaf undersides reveals spores produced singly or in very short chains; however, the profuse white hairs of the leaf may obscure this sign. Severely infected leaves will turn yellow, then brown. With time the brown leaves may collapse and dry up. Leveillula infects only the older leaves; the younger leaves escape infection until they mature.
Powdery mildew caused by Erysiphe cichoracearum causes less severe symptoms. The flat, low-growing white to gray mycelia and spores of this fungus develop on the outside of flower bracts and on upper surfaces of both young and old leaves. The fungus produces abundant spores in long chains. Underlying tissue will turn brown.
Comments on the Disease
Spores are dispersed by wind. Reports suggest that L. taurica from artichoke may be a different race than the L. taurica that occurs on tomato and other hosts.
Management
If you see early symptoms, check weekly to monitor progress of the disease. Fungicides are not needed unless the disease becomes severe.
| 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. | TRIFLOXYSTROBIN | |||
| (Gem 500 SC, Flint Extra) | 3.0–3.8 fl oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| B. | MYCLOBUTANIL | |||
| (Rally 40WSP) | 4 oz | 24 | 3 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) | ||||
| COMMENTS: Do not apply more than 0.4 lb a.i./acre per year or exceed 4 applications per year. | ||||
| C. | AZOXYSTROBIN | |||
| (Quadris) | 11–15.5 fl oz | 4 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| COMMENTS: Do not apply more than one application before alternating with a fungicide that has a different mode of action group number. Do not make more than 4 applications/acre per crop year. Do not apply more than 2.88 qt (1.5 lb a.i.)/acre per crop year. | ||||
| D. | FLUOPYRAM/TRIFLOXYSTROBIN | |||
| (Luna Sensation) | 7.6 fl oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate-dehydrogenase inhibitor (7)/quinone outside inhibitor (11) | ||||
| E. | QUINOXYFEN | |||
| (Quintec) | 4–6 fl oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Azanapthalenes (13) | ||||
| F. | BACILLUS PUMILUS | |||
| (Sonata)# | 2–4 qt | 4 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Microbial (44) | ||||
| COMMENTS: Check with organic certifier to determine which products are organically acceptable. | ||||
| G. | SULFUR | |||
| (Microthiol Disperss)# | 10–20 lb | 24 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M2) | ||||
| COMMENTS: Begin application when disease first appears and repeat at 7- to 10-day intervals as needed. | ||||
| ‡ | 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 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. |