Woolly ash aphid is a key pest in nursery production of ash, Fraxinus spp. Damage from aphid feeding can be severe and lasting. Although this pest is relatively common, little information of its activity in nurseries and landscapes has been published.
Most of the aphids described on ash are in the tribe Pemphiginae. Some Pemphigid aphids can infest the root systems of conifers. These aphids are described as woolly aphids due to the light colored waxy strands secreted by some stages.
There are several species of aphids that have been listed as occurring on ash trees (Blackman and Eastop, 1994). Walker (1969) mentions Procipihilus (Pemphigus) americanus Wlk. specimens collected from ash in California, Colorado, Oregon, Utah, and Canada. In the Northwest Zak (1965) mentions P. americanus using ash as an alternate host in rotation with Noble fir, Abies procera Rehd. The aphid, Prociphilus fraxinifolii, (Meliarhizophagus fraxinifolii) occurs on the roots and leaves of ash trees in a mutualistic asociation with the ash-tree bolete fungus Boletinellus merulioides (Grundrett and Kendrick, 1987). In California, P. fraxinifolii, is reported on Modesto ash, F. velutina (Anonymous, 1998). Carver (1980) reports on a parasite of P. fraxinifolii (Riley) on ash in Iowa. In Sichuan Province in China, the aphid Prociphilus fraxini (F.) occurs on chinese ash, F. chinensis, occasional outbreaks causing considerable damage. P. bumeliae are reported from European Ash, Fraxinus excelsior (Blackman and Eastop, 1994). White Ash, Fraxinus americana, are listed as hosts of P. americanus, P. fraxinifolii, P. oriens, P. pergandei, and P. probosceus (Blackman and Eastop, 1994) . Green Ash, F. pennsylvanica, host P. americanus, P. fraxinifolii, and P. probosceus (Blackman and Eastop, 1994). Essig (1911) describes populations of P. americanus (Pemphigus fraxini-dipetalae) from California Mountain Ash, F. dipetala.
Last modified - 4/23/03
Aphids can have very complex biologies. They may have multiple host plants and widely varying shapes through the year. Additionally there may be confusion due to specialized terminology concerning aphid biology.
Ash trees are considered the primary host for P. americanus and noble fir trees, the secondary host. P. americanus is thought to overwinter on ash as eggs placed in bark crevices (Bugwood, 2000). The eggs hatch (eclose) in early spring and produce wingless females which reproduce without mating (parthenogenesis). This aphid form is the fundatrix or stem mother and her progeny are termed fundatrigenia, fundatripuriae, or apterous (wingless) viviparae (live birth) and also reproduce parthenogenetically. A wee bit confusing! Hang on, there's more.
The fundatrigenia give birth to winged (alate) aphids called Sexuparae. This winged stage allows the aphid to disperse, generally to the alternate host, the noble fir. This aphid form has both male and egg-laying (oviparae) female offspring. These offspring can mate and are known as Sexuales. The female Sexuales lay the overwintering eggs on the primary host, ash trees.
In the Pacific Northwest, root aphids can be found year round on both noble fir and ash trees according to nursery producers and research in Christmas tree production.
|
wingless ash aphid (apterous) |
waxy adult aphid (fundatrix) |
|
newly emerged winged aphid (alate) |
winged adult (alate) |
|
note the aphid stylet or beak |
root aphid stage |
|
winged aphid |
Last modified - 7/22/02
Damage from woolly aphid feeding can be extensive. Aphid feeding induces curling in growing plant tissue. Enation or cupping of tissue can occur from the feeding of a single aphid. This damage is long lasting and can gravely impact the quality of nursery grown ash trees. The most critical economic damage in shade tree production occurs when the tree terminals are affected, often causing cull trees.
Honeydew produced by the aphids is copious and may promote the growth of black sooty mold.
Last modified - 7/22/02
|
curled leaves on new growth |
aphid honeydew |
|
aphids under tape |
Little is know about specific natural enemies associated with wooly ash aphid. Carver (1980) reports on a parasitic wasp, Aphelinus prociphili, of P. fraxinifolii (Riley) on ash in Iowa. Wu and Fang (1987) report of the importance of the predatory ladybeetle Callicaria superba Muls. The author's research has indicated there are a variety of natural enemies associated with this aphid. The natural enemy complex generally does not keep plant damage below an acceptable level in nursery production. The natural enemies we have seen associated with wooly ash aphid in Oregon are as follows:
|
sryphid fly (egg) |
spiders |
| ladybeetles |
parasitic wasps |
Last modified - 7/22/02
Some factors to consider with chemical control are
- mode of action,
- residual,
- potential for phytotoxicity,
- selectivity,
- application efficiency,
- re-entry interval, and
- toxicity.
More selective aphidicides may be indicated for sites using biological control or interested in conserving natural enemies. Oils and soaps, though they can kill on contact, have no residual, leaving immigrating natural enemies unharmed. Although homemade concoctions of oil and soap applications may very well have an effect on the aphids, the base products are not formulated for plant use and may cause phytotoxicity. It is also important for applicators at commercial nurseries to use pesticides legally registered by the EPA and licensed in their state.
Toxicity and re-entry levels vary tremendously.
Check the PNW Insect Management Hanbook for current recommendations for control of aphids on nursery stock.
Last modified - 3/15/05
Anonymous. 1998. Woolly Ash Aphid. Urban Pest Notes. Agricultural Commissioner. Santa Barbara County. http://www.co.santa-barbara.ca.us/agcomm/ashaphid.htm
Blackman, R.L. and V.F. Eastop. 1994 Aphids on the World's Trees: An Identification and Information Guide. CAB International. 987 pp.
Brundrett, M.C. and B. Kendrick. 1987. The relationship between the ash bolete (Boletinellus merulioides) and an aphid parasitic on ash tree roots. Symbiosis. 3: 3, 315-320.
Bugwood. 2000. Woolly Ash Aphid: Guide to Ash Pests. The Bugwood Network. University of Georgia, Tifton, GA. http://www.bugwood.org.
Carver, M. 1980. A New Species of Aphelinus Dalman (Hymenoptera: Chalidoidea: Encyrtidae). Pro. Entomol. Soc. Wash. 82(4) pp. 536-540.
Essig, E.O. 1911. Aphididae of southern California. VII. Pomona Coll. J. Entomol. 3: 523-57.
Smith, Clyde F. 1969. Pemphiginae Associated with the roots of Conifers in North America (Homoptera: Aphididae). Annals of the Entomological Society of America. Vol.62, no. 5.
Wu, C.B. and S.Y. Fang. Biological notes on the Chinese ash woolly aphid Prociphilus fraxini Fabricus [Sichuan Province]. Acta ento Sinica. 26, no. 2 (May 1983): p. 161-164.
Zak, B. 1965. aphids feeding on mycorrhizae of Douglas-fir. Forest Sci. 11: 410-1.
Last modified - 4/23/03
Apterous Viviparae: Fundatrigenia, wingless aphid produced by live birth, parthenogenetically, from the fundatrix.
Fundatrices: pleural of fundatrix.
Fundatrix: mature wingless stem mother which hatches from over-wintering eggs.
Fundatrigenia: Apterous viviparae, wingless aphids produced by live birth, parthenogenetically, from the fundatrix. Fundatrispuriae is synonym.
Fundatrispuriae: Apterous viviparae, wingless aphid produced by live birth, parthenogenetically, from the fundatrix. Fundatrigenia is synonym.
Heteroecy: host alternation during life cycle. Usually involves a primary host and a secondary host.
Oviparae: sexual females
Pathenogenesis: reproduction without mating.
Sexuales: the mature, winged form of the sexuparae. These aphids mate and the females produce eggs.
Sexuparae: the progeny of the stem mother, males and females.
Stem mother: mature wingless fundatrix which hatches from over-wintering eggs.
Last modified - 4/23/03
The author would like to thank the following people for their contributions:
Thirza Collins, nursery research technician, for hours of trekking in the rain and mud to collect samples of ash and her wonderful diligence in all aspects of her work;
Becky , Master Gardener volunteer, for seemingly endless hours scrutinizing samples;
Dennis Brown, Master Gardener volunteer, for inspiring photography on a moment's notice.
The Oregon Department of Agriculture for their support of research on Woolly Ash Aphid.
Last modified - 4/23/03