Hackberry Woolly Aphid

HACKBERRY WOOLLY APHID Integrated Pest Management for Home Gardeners and Landscape Professionals An introduced woolly aphid (Shivaphis celti), sometimes called Asian woolly hackberry aphid, infests the widely planted Chinese hackberry (Celtis sinensis) and other Celtis species. This hackberry woolly aphid also occurs from Florida to Texas and northward to at least Illinois. It also occurs in much of Asia. IDENTIFICATION Often the first observed sign of a hackberry woolly aphid infestation is the Figure 1. Honeydew drops and aphid Figure 2. Winged adult woolly hack- nymphs on Chinese hackberry fruit sticky honeydew it produces (Figure 1). berry aphid. petiole. The aphids also secrete pale wax, which covers their bodies (Figure 2). These woolly aphids on shoot terminals and leaves appear as fuzzy, bluish or white masses, each about 1/10 inch or less in diameter (Figure 3). Winged forms have distinct black borders along the forewing veins and their antennae have alternating dark and light bands (Figure 4). Check for the insects to confirm that the cause of honeydew is aphids and not the citricola scale (Figure 5). Citri- cola scale (Coccus pseudomagnoliarum) Figure 3. Wax-covered aphids and Figure 4. Dark antenna and wing marks is the only other honeydew-producing honeydew on Chinese hackberry. on a hackberry woolly aphid. insect that infests hackberry at annoying levels in California, and it is most common in the Central Valley on citrus and hackberry. Citricola scale females and older nymphs (immatures) are brownish to gray, oval, slightly dome shaped, and occur on twig bark from fall through spring (Figure 6). Because the scales are immobile most of their life and their mottled gray to brown color blends in with bark, these scales are easily overlooked. In the spring female scales pro- duce tiny flattened, orangish nymphs Figure 5. A just-born aphid nymph (cen- Figure 6. Citricola scale females on twig that settle and feed on the underside ter), wax-covered aphid adult, and citri- and tiny nymphs on underside of leaves. of leaves during spring and summer, cola scale nymphs (bottom right). then move in fall to overwinter on bark. PEST NOTES Publication 74111 Statewide Integrated Pest Management Program August 2014 August 2014 Hackberry Woolly Aphid For more information, see Pest Notes: can be warranted on tall trees where Scales. the honeydew-producing insects may be located too high to easily observe, DAMAGE where there is a low tolerance for drip- This aphid is a pest because it produces ping honeydew, and when managing copious honeydew excretions upon many trees, such as along city streets which blackish sooty mold grows and parking lots. creating a sticky mess on leaves and surfaces beneath infested trees. How- Monitor honeydew with the bright ever, no long-term or serious damage yellow cards sold for evaluating insec- to hackberry trees has been found after ticide spray coverage and calibrating years of aphid infestations. Insecticides sprayers. Cards develop distinct blue apparently are not warranted to protect dots upon contact with honeydew or Figure 7. A black aphid egg overwinter- the health or survival of infested trees water droplets. These droplet monitoring on a twig bud. but are applied when honeydew excre- ing cards generally must be mail or- enemies is one long-term possibility for tions are intolerable to people. dered and are different from the yellow managing this pest. sticky traps used to monitor winged insects. Regularly monitor honeydew LIFE CYCLE In many California situations, natural beneath plants, such as the number of Hackberry woolly aphid adults, either enemies do not provide adequate bio- drops during four hours on the same winged or wingless, give live birth to logical control of this aphid. Neverthe- time of day once a week. Label and aphid nymphs during most of the sea- less, avoid spraying hackberry with save the cards from each monitoring son when hackberry leaves are present. broad-spectrum, persistent insecticides date, and visually compare the cards Spring and summer adults are all re- that kill natural enemies; because the among sample dates. For more infor- productive females. In the fall, winged citricola scale, another major hackberry mation on monitoring honeydew, see males are produced; the aphids mate, pest, is well controlled by parasites in Pests of Landscape Trees and Shrubs: An and females lay eggs that overwinter some locations. Integrated Pest Management Guide. on branch terminals (Figure 7). Eggs hatch in the spring as the hackberry Cultural Control Chemical Control produces leaves. In the San Joaquin Before applying insecticide, make sure Valley, hackberry woolly aphid popula- Provide trees with appropriate soil plants are receiving appropriate cul- tions typically are highest in the spring moisture, avoid compacting topsoil, tural care and take steps to conserve and fall with lower numbers and less and prevent prolonged waterlogging natural enemies. Completely read and honeydew production during the sum- of soil near trunks. Excess irrigation follow the product label instructions mer. The insect has many generations promotes certain root decay pathogens for the safe and effective use of the per year. and may contribute to a malady of un- determined cause that has killed many insecticide. Insecticides can have unin- MANAGEMENT Chinese hackberry in some locations in tended effects, such as contaminating California. Avoid fertilizing hackberry water, poisoning pollinators and natu- Inspect leaves for waxy masses and unless nutrient deficiency has definitely ral enemies, and causing secondary insects to be sure that aphids are the been diagnosed. Excess nitrogen has pest outbreaks. cause of annoying honeydew. Citricola been shown to increase aphid num- scale, described above, also produces bers on certain other plant species. A Nonresidual, Contact honeydew and is easily overlooked. forceful stream of water will dislodge Insecticides Because plant health apparently is and kill some aphids and wash away not threatened, apply insecticide only Where trees can be sprayed, completely honeydew on plants small enough for where annoyance from honeydew can- covering shoot terminals and the un- hosing to be practical. not be tolerated. dersides of leaves with a nonpersistent, contact insecticide can provide partial Honeydew Monitoring. Water- Biological Control control of hackberry aphids. Available sensitive cards can be used by land- The convergent lady beetle, multicol- nonpersistent, contact insecticides scape managers to efficiently monitor ored Asian lady beetle, syrphid flies, include narrow-range or horticultural honeydew dripping from trees. This and lacewing larvae are common aphid oils (e.g., Bonide Horticultural Oil), in- technique provides a consistent mea- predators. No parasitic wasps or other secticidal soap (Safer Brand Insect Kill- sure of changes in aphid abundance natural enemies specific to this pest ing Soap Concentrate II), and pyrethrin and helps you decide when to take con- species have been reported in Cali- products, which are often combined trol action and afterwards to evaluate fornia. Several parasitic wasps of the with piperonyl butoxide (Ace Flower t h e e ff e c t i v e n e s s o f y o u r a c t i o n s . T h e Trioxys species attack this aphid in Asia, & Vegetable Insect Spray, Garden Tech effort required to monitor honeydew and the introduction of these natural Worry Free Brand Concentrate). ◆ 2 of 4 ◆ August 2014 Hackberry Woolly Aphid These insecticides have low toxicity to people and pets and relatively little adverse impact on the populations of pollinators and natural enemies and the benefits they provide. These products will give only partial control because aphids’ woolly wax protects them from sprays; and it is difficult to obtain thorough spray coverage of aphids, especially on large trees. Be- cause these insecticides provide no residual control and aphids have several generations each year, more than one application per season is generally needed. Dormant Spray. Thorough application Figure 8. When applying systemic pesticides to trees, spray bark or drench or inject of horticultural oil (sometimes also soil whenever possible as directed on product labels instead of injecting or im- called supreme, superior, or narrow- planting trees with pesticide. range oil) to twig terminals during the dormant or delayed dormant season (after buds swell, but before leaves Bonide Annual Tree & Shrub Insect and pollinators that feed on nectar and open) can kill overwintering eggs on Control Concentrate), which can easily pollen. Although hackberry’s tiny flow- twigs. Delayed dormant spraying is be drenched into soil around the tree ers are wind pollinated, do not apply unlikely to give complete control of trunk using the mix-and-pour method systemic insecticides to plants during aphids and will not control aphids that as directed on the product labels. The flowering or shortly before flowering; fly in from other hackberry trees after neonicotinoid dinotefuran is also avail- wait until after plants have completed leaves have opened. However, dormant able for aphid control by home users their seasonal flowering unless the oil spray provides good control of cit- (Green Light Tree & Shrub Insect Con- product’s label directions say other- ricola scale, and aphid reduction could trol with Safari 2G and Ortho Tree & be a side benefit if treatment is needed Shrub Insect Control Granules). Dinote- wise. With soil application, when pos- for scales.

Load more