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The Woolly Ash Aphid, Prociphilus franxinifolii, is one of the most troublesome insects found on Modesto ash, Fraxinus velutina. These aphids attack the young foliage in the spring as soon as the leaves open. Feeding aphids cause leaves to curl and form pseudo galls in masses on tips of twigs. Colonies of aphids can be found in curled leaves and shower honeydew on cars and sidewalks beneath the trees. In the summer and fall, winged aphids can fly about creating a nuisance to homeowners and their pets.
Host: Ash species in the genus Fraxinus are the preferred host. Modesto ash is a common host of this aphid.
Injury: Aphid feeding distorts the new spring growth, causing curled and cupped leaves that remain affixed at the ends of twigs. Honeydew, or undigested tree sap, is excreted by the aphids and falls on cars and sidewalks beneath the trees. The sooty mold that often develops on honeydew can inhibit photosynthesis and harm the finish on cars.
Description: An adult woolly ash aphid is approximately 2.5 mm long. Aphids are covered by a woolly wax and globs of clear fluid. Glands, located on the head, and in three longitudinal rows on the abdomen, exude a wax that gives the aphid it's woolly appearance. The head, thorax, antennae, and legs are blackish-brown, while the abdomen is yellow-green.
Life Cycle: The woolly ash aphid overwinters on ash. The spring generation lives in colonies under curled leaves at the tips of twigs. The preferred habitat is the sucker growth around the base of the tree as well as suckers that grow from the trunk within the inner tree canopy. When these suckers are pruned away, the remaining aphid population may be so small as to be rarely noticed, but if the main outer branches are pruned severely in such a way as to encourage rapid, extensive sucker growth in the canopy, the pest problem may become severe.
Controls: Natural predators such as green lacewing and syrphid fly larvae feed on this aphid, however, augmented releases may be necessary in spring to achieve better control. Natural predators may be available through your local farm supply or gardening store. Sources for biological control agents can be found in the Department of Pesticide Regulations' publication, Suppliers of Beneficial Organisms in North America.
Insecticidal soap, horticultural oils and Merit have been recommended for use against the aphid. Merit is a broad spectrum, systemic insecticide, that controls by both contact and ingestion and can be sprayed on the foliage or soil, or injected into the soil. Consider adding a wetting agent to foliar applications, to assist in penetrating the aphid's waxy defense. Soil applications have the added benefit of reduced drift. It may be difficult to reach the tops of ash trees without the use of high pressure sprayers, not often readily available to homeowners. Applications should occur during the early spring, before massive leaf curling occurs. Consult a professional pest control company for assistance in treating this problem.
| Santa Barbara County Agricultural Commissioner's Office 263 Camino del Remedio Santa Barbara CA 93110 (805)681-5600 | July 1998 |