Description of the Pest
Prune limb borer and American plum borer are sporadic pests in young almond orchards and in bark injuries on mature trees. They occur from Tehama to Merced counties on all major almond cultivars, but in young trees are found mostly on Carmel, Sonora, and Price. Adult moths have gray forewings with brown and black marks and have a wingspan of about 0.75 inch. They overwinter in a cocoon within the tree. Adult moths emerge in April and May. The mature larva is about 1 inch long with a dull white or pinkish body. Females lay eggs near pruning wounds, in scaffold crotches of young trees, in areas where bark has been damaged by trunk shakers on mature trees, or near graft unions or on crown galls.
Damage
Larvae bore into trees, leaving reddish orange frass and gum pockets. The boring is most damaging to the scaffold crotches or graft unions of young trees. Vigorous trees will heal over, but with heavy, prolonged infestations, scaffolds may break with wind or a heavy crop. Boring in callus formed under trunk-shaker bark injuries can greatly enlarge the initial injury, and also introduces spores of the Ceratocystis canker fungus, leading to subsequent trunk cankers that can girdle scaffolds and may ultimately lead to tree death.
Management
- Monitor young orchards in spring and summer for frass and gum pockets.
- If larvae are present, spray trees with a hand-held sprayer from 1 foot above the scaffold crotch to 1 foot below, two to three times during the growing season.
- Make the first application in mid- to late April, and subsequent applications at 6-week intervals.
Efficacy is improved if the trunk is painted with a latex paint to protect against sunburn immediately following a trunk spray. The paint helps to preserve the insecticide and give protection over a longer period of time. On mature trees, loose bark can be removed from trunk shaker injuries and wounds treated as described above for young trees.
| 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 harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used. | ||||
| A. | CARBARYL* | |||
| (Sevin XLR Plus) | 2–5 qt | 12 | 14 | |
| MODE-OF-ACTION GROUP NUMBER1: 1A | ||||
| COMMENTS: Do not exceed 15 lb/acre per season. | ||||
| * | Permit required from county agricultural commissioner for purchase or use. |
| ‡ | 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 | Rotate pesticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; pesticides with a 1B group number should be alternated with pesticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee). |