Symptoms and Signs
Individual leaves on spurs or shoots wither and die in early summer. The fungus kills the petioles and the axillary buds. Leaf blades disintegrate, but diseased petioles stick on tree during winter. When the axillary bud is killed, spurs do not develop.
Comments on the Disease
The fungus survives on dead petioles. Spores are spread by rain, and disease is favored by wet spring weather. Leaf blight is usually not very severe or widespread; it rarely destroys more than 20% of the leaves in one season. Repeated early death of leaves will weaken trees, however, and may contribute to loss in yield as a result of the loss of spur development.
Management
Apply a fungicide during the period from bloom through early spring. Make the first application during early leafing, which usually occurs at full bloom to petal fall. Pink bud is too early for control.
| 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 | |||
| (Abound) | 12.0–15.5 oz | 4 | 28 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| COMMENTS: Do not apply more than two sequential sprays before alternating with a fungicide that has a different mode of action. Do not apply more than four applications of strobilurin fungicides per year or apply more than 92.3 fl oz/acre per season. | ||||
| B. | TRIFLOXYSTROBIN | |||
| (Gem 500SC) | 1.9–3.8 oz | 12 | 14 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| COMMENTS: Do not apply within 14 days of harvest or after hullsplit. Do not make more than four applications per season and no more than two sequential sprays of QoI or SDHI fungicides to limit the potential for the development of resistance. | ||||
| C. | MYCLOBUTANIL | |||
| (Laredo EW) | 9.6–15.3 fl oz | 24 | 90 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation (sterol) inhibitor (3) | ||||
| COMMENTS: Apply in 400 gallons water/acre. Do not make more than two successive applications and no more than three per season to limit the development of resistance. Use in rotation with different FRAC groups. | ||||
| D. | CAPTAN | |||
| (various 50WP) | 8 lb | 96 (4 days)
|
See label | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M4) | ||||
| COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays. | ||||
| E. | ZIRAM | |||
| (Ziram 76DF) | 8 lb | 48 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3) | ||||
| COMMENTS: Do not apply more than 32 lb/acre per season. | ||||
| ‡ | 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 these two intervals is the minimum time that must elapse before harvest may occur. |
| 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. |