Description of the Pest

(View aphid identification photos online)

The leaf curl plum aphid is often found inside curled leaves. It is shiny, has no wax covering, and varies considerably in color from green to brownish green or brownish yellow. This aphid overwinters in the egg stage near the base of buds. In spring it rapidly increases in number on new foliage, causing affected spurs to develop tightly curled leaves. In May, the aphids migrate from the orchard to summer host plants in the family Asteraceae (members include daisy, dandelion, and sunflower). Leaf curl plum aphid migrates back to prune orchards in the fall (September) to feed, mate, and lay eggs. The eggs hatch just before bloom, generally in late February.

Damage

Colonies of this pest cause leaves to curl tightly. Often only one limb or a portion of a limb is infested early in the year. Leaf curl plum aphid produces plenty of honeydew and large numbers of this pest may reduce the tree growth and fruit sugar content.

Management

Several natural enemies are important in the control of aphids in the orchard, but large aphid numbers may require pesticide application. The best indicator of leaf curl plum aphid infestation risk is the orchard history.

Biological Control

There are many natural enemies that feed on leaf curl plum aphid; however, fruit size may still be reduced and curled leaves will not uncurl after aphids are suppressed. The relatively recent introductions of Aphidius colemani has led to substantial levels of parasitism of this aphid. Important predators include brown lacewings, green lacewings, lady beetles, soldier beetles, and syrphid flies.

Organically Acceptable Methods

Use biological control and sprays of mineral oil (narrow range oil), neem oil, or neem oil plus insecticidal soap in a certified organic crop.

Monitoring and Treatment Decisions

The best time to treat is from late October through the delayed-dormant period. The timing of aphid control treatment is largely determined by past aphid pressure and scale control plans. If aphids are a chronic problem in the orchard and scale control in the dormant/delayed-dormant is not needed, treatment in late fall or early dormancy (late October through November) is a very effective way to manage these pests and is less likely to create water quality problems caused by pesticide runoff than applications during the rainier season in January and February. If scale treatment is needed, a dormant scale spray can be combined with aphid treatment to save costs (one spray for both pests compared with a fall spray for aphid and a dormant/delayed-dormant spray for scale).

If leaves are still on trees after mid-October, which is common in many orchards, both aphids and parasites can be present. Oil treatments are not recommended at this time because they are very damaging to parasite populations and not effective for aphid control.

A postharvest foliar zinc sulfate application will provide zinc to the trees as well as hasten leaf fall. Without the leaves on the tree, the aphid life cycle is disrupted. Zinc sulfate (36%) foliar fertilizer applied at 10 to 20 pounds per acre in early to mid-October helps in this process. When orchards are dry in the fall, zinc sulfate sprays may not accelerate defoliation.

Dormant Monitoring

If the fall treatment is not applied, be sure to monitor during dormancy (for more information, see Dormant Spur Sample) or in the spring. If dormant monitoring indicates treatment is necessary and scale control is not needed, two applications of oil at bloom can control aphid very effectively without the need of a dormant spray. Parasites are not active at bloom, and therefore, are not affected by the bloom oil sprays.

Spring Monitoring

If aphids have been a problem in the past or if a dormant or delayed-dormant application was not applied, monitor leaf curl plum aphid in spring along with mealy plum aphid. Follow the monitoring guidelines in Spring/Summer Monitoring to determine if treatment is necessary.

Dormant and Delayed-Dormant Sprays

Dormant or delayed-dormant applications of many pesticides applied within 48 hours prior to rain events carry increased risks of surface water contamination resulting from orchard runoff, especially when the ground is saturated. Follow the Dormant Insecticide Contamination Prevention regulations when applying during this time of the year. Be especially careful when applying pyrethroid (MOA 3A) or organophosphate (OP; MOA 1B) insecticides, because they are highly toxic to aquatic life.

Pesticide spray drift risk is highest during dormant or delayed-dormant spray applications due to lack of leaves to slow the progress of spray through the canopy. Growers should consider using Gear Up, Throttle Down or other spray practice to reduce spray drift including low drift nozzles, reduced sprayer fan speeds and use of synchronized sprayers to restrict spray movement. Currently, spray drift from pyrethroid and, to a lesser degree, organophosphate pesticide applications are of major concern regarding spray drift impacting surface water quality.

Pesticides and Natural Enemy Releases

Important Links

• Photos of aphids