HONEYSUCKLE WITCHES` BROOM APHID
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HONEYSUCKLE WITCHES` BROOM APHID
PEST DIAGNOSTIC CLINIC Laboratory Services Division, University of Guelph 95 Stone Rd. West, Guelph, Ontario N1H 8J7 Phone: (519) 767-6299 E-mail: [email protected] Web: www.guelphlabservices.com HONEYSUCKLE WITCHES' BROOM APHID During the past several years, an aphid has caused injury to honeysuckle, Lonicera spp., in Ontario. This aphid, Hyadaphis tataricae, is of Asian origin, and was likely imported into Canada on infested Lonicera from Europe. Honeysuckle aphids are small (less than 2 mm), pale green to cream coloured, and covered with a powdery, waxy material. They feed in colonies of up to several hundred individuals on the tips of Lonicera branches. As a response to honeysuckle aphid feeding, growth of the new shoots is slowed considerably. In addition, numerous buds are produced in the axils of leaves and branches, which develop into shoots causing a broom-like effect on the tips of the branches called witches' brooming. Leaves in these witches' brooms are curled and dwarfed, and as the season progresses, they droop and eventually die. The witches' brooms caused by the aphids are obvious and unsightly, and are easily seen from a distance, especially in winter and early spring when most of the leaves have fallen. The entire life cycle of this aphid is completed on honeysuckle, which is the only known host. The aphids overwinter as eggs on infested branch tips, which hatch in early spring as the honeysuckle buds are swelling and beginning to grow. Young aphids feed on the mid-rib of the leaves, causing the infested leaf to fold upwards, enclosing the aphids in a pouch where they continue to feed. Initially the aphids are wingless; however, winged individuals may be found by the 3rd generation. Winged aphids disperse continuously throughout the remainder of the summer. The honeysuckle aphid reproduces throughout the summer by bearing live young. Egg laying female aphids begin to develop in late August and lay eggs from September to the end of the growing season, on honeysuckle branches. Honeysuckle has long been regarded a low maintenance plant, requiring very little in the way of pest control. However, these aphids can cause severe injury to the shrubs beginning with stunting and growth deformation in the early stages of infestation, and ending with the eventual death of the plant should the infestation go unchecked. Approximately 3 years are required from the onset of infestation for the shrub to be entirely infested. CONTROL 1. Lonicera spp. and varieties differ widely in their tolerance to these aphids. If you are contemplating using Lonicera as a landscape species, do not choose varieties that are susceptible to the aphid. If susceptible varieties are severely damaged in the landscape, consider replacing them with those that are resistant. Often botanical gardens and arboreta will have collections of these shrubs for viewing their various horticultural characteristics. The following list is adapted from published literature and from observations at the University of Guelph Arboretum: Resistant Lonicera caerulea * L. caerulea edulis Tolerant L. ledebourii L. maackii Susceptible L. x amoena L. x bella "Dropmore" PDCF-111 (Revised 2012-06-25) Resistant L. caerulea dependens L. caerulea viridifolia L. tatarica "Morden Orange" * L. heteroloba * L. altmannii Tolerant L. maximowiczii L. minutiflora L. x meundeniensis xanthocarpa L. orientalis L. syringantha L. discolor L. morrowii L. syringantha "Grandiflora" L. tatarica "Arnold Red" "Rubra" "Beavermor" L. x salicifolia L. tatarinovii L. xylosteum * L. standishii L. ruprechtiana * L. chrysantha Susceptible L. korolkowii "Zabelii" L. microphylla L. myrtilloides L. x notha L. tatarica "Grandiflora" "Rosea" "Bytown" "Hack's Red" "Red Giant" * Exceptional species in appearance, which are recommended as substitutes for susceptible Lonicera. 2. In order to remove the eggs, which are overwintering on the shrubs, prune out the infested branches well below the witches' broom present on the terminal from the previous year. This must be done before the buds begin to break. 3. In order to kill aphid eggs remaining on the plant after pruning, a dormant oil application should be made before the buds break in early spring. 4. After bud break, to protect young foliage from winged aphids, which can migrate to noninfested bushes, it may be wise to use chemical products. Please contact a local garden centre for product advice. You may also wish to visit the Ontario Ministry of Agriculture Food and Rural Affairs “Online Gardener’s Handbook” http://www.omafra.gov.on.ca/english/crops/gardbk/ghlinks.htm. ** Special thanks to Henry Kock for his observations at the University of Guelph Arboretum. R.T. Wukasch PDCF-111 (Revised 2012-06-25)