Giant conifer aphid christmas tree

Contents

Aphids Tree Disease – How To Treat Tree Aphids And Honeydew Dripping

When you see tree leaves dripping sap, the usual cause is tree aphids. These pesky insect pests can cause serious stress to your trees and lead to disease. Learn more about aphids on tree limbs and foliage and what you can do for tree aphid treatment.

What are Tree Aphids?

These tiny, soft-bodied, pear-shaped insects can be almost any color. Aphids on tree foliage and shoots feed by sucking fluid from the tree through a slender mouthpart called a proboscis. They feed in clusters, usually on the undersides of leaves near the point where the leaf attaches to the stem, or on tender young shoots and buds. As they feed, they secrete a sticky fluid called honeydew. When enough aphids are feeding on the tree, this honeydew will begin dripping from the leaves.

Aphids Tree Disease Issues

Some tree diseases are spread by aphids, especially fungal diseases. Tree disease is much more serious than aphid infestations, and can kill or seriously damage a tree. To prevent the spread of aphid tree disease, keep the tree as healthy as possible to support its natural defense against disease and control the aphids as much as possible.

Tree Aphid Treatment

The first step in controlling aphids is to control the ants that feed on the honeydew they secrete. Ants protect aphids from their natural enemies to ensure a continued supply of honeydew. Bait traps are effective, but read the label carefully, and only use traps that are safe around children, pets and wildlife.

Tree aphids have a number of natural enemies that help keep their populations in check. When trying to control aphids, keep in mind that you want to preserve these beneficial insect populations. Beneficial insects are much more effective at controlling aphids than insecticides, and the use of strong insecticides can make aphid infestations worse.

You can remove aphids from small trees with a strong spray of water from a hose. Aphids that are knocked off of a tree are unable to return. Spraying the tree with neem oil or insecticidal soap helps control aphids without harming beneficial insects, but the spray has to come into direct contact with the aphid to be effective. Spray the tree until the insecticide drips from the foliage. It may take several applications to eliminate the aphids.

Insecticides that contain ingredients such as permethrin, acephate, malathion, diazinon, or chlorpyrifos are effective against aphids, but they are also effective against beneficial insects and may only make the problem worse. Use them only as a last resort.

Now that you know a little about what causes tree leaves dripping sap, you can take the correct steps in preventing and treating aphids on tree foliage.

Colorado State University

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by W.S. Cranshaw 1 (1/19)

Quick Facts…

  • Aphids are found on almost all types of plants and a few species can cause plant injury.
  • Some aphid species can curl the new leaves of some types of plant.
  • Feeding aphids excrete honeydew, a sticky fluid that can cause nuisance problems.
  • Natural enemies of aphids include lady beetles, flower fly larvae, lacewing larvae, and parasitic wasps.
  • Exposed aphids can be controlled by insecticides, insecticidal soaps and sometimes with a strong jet of water.

Figure 1: Aphids on the underside of an oak leaf.

Figure 2: Leafcurling produced by aphids on snowball viburnum.

Aphids are the most common insects found on trees, shrubs, and garden ornamental plants. Over 350 different aphid species occur in the state but most can feed on only a few species of plants. However, with so many kinds of aphids, few plants grown in Colorado do not support at least one aphid. Most species rarely injure plants or even attract attention, but a few aphid species do cause problems (Table 1).

Aphids feed by sucking sap from plants. When the number of aphids on a plant are very high for an extended period, their feeding can cause wilting and sometimes even dieback of shoots and buds. Some aphids can cause leaf curling when the insect infests emerging leaves.

Sometimes problems with aphids do not primarily involve plant injury but instead their production of sticky honeydew. Honeydew is the waste material excreted by aphids and certain other phloem-sucking insects (e.g., soft scales, whiteflies, some leafhoppers). It may cover leaves, branches, sidewalks and anything that lies beneath a infested plant material. Grayish sooty mold grows on the honeydew, further detracting from plant appearance. Ants, yellowjacket wasps, flies, and bees are usually attracted to plants that are covered with honeydew.

Table 1: Some common aphids associated with trees, shrubs and ornamentals in Colorado. Those marked with an * commonly cause leaf curling distortions in new growth.

Scientific name(Common name) Host plant
Acyrthosiphum pisum (pea aphid) Sweet pea, other legumes
Aphis helianthi (sunflower aphid) Red twig dogwood, yucca and many flowering plants in summer
Aphis nerii (yellow milkweed aphid) Milkweeds (Asclepias)
Aphis spiraecola (spirea aphid) Spirea
Aphis viburnicola (snowball aphid) Snowball viburnum
*Brachycaudus helichrysi (leafcurl plum aphid) American Plum
Caveriella aegopodii (willow-carrot aphid) Various European willows
Chaitophorus populicola Populus
Chaitophorus populifolii Populus
Chaitophorus viminalis Willow
Cindara spp. (giant conifer aphids) Pines, juniper, spruce
*Cryptomyzus ribis (currant aphid) Currant
*Dysaphis plantaginea (rosy apple aphid) Apple
Dysaphis tulipae (tulip bulb aphid) Dutch iris, tulip
Eriosoma lanigerum (woolly apple aphid) Elm, apple, crabapple
*Eriosoma amiercanum (woolly elm aphid) Elm, amelanchier/Serviceberry
Essigella spp. Pines
Eulachnus spp. Pines
*Hyadaphis tataricae (honeysuckle witches’ broom aphid) Tatarian honeysuckle
Hyalopterus pruni (mealy plum aphid) Prunus
Macrosiphum rosae (rose aphid) Rose
Macrosiphum euphorbiae (potato aphid) Rose, many flowers
Macrosiphum albifrons (lupine aphid) Lupine
*Meliarhizophagous fraxinifolii (leafcurl ash aphid) Green ash
Monellia caryae (American walnut aphid) Walnut
Myzocallis tiliae (linden aphid) Linden
Myzocallis alhambra (western dusky-winged oak aphid) Bur oak
Myzocallis ulmifolii (elm leaf aphid) Elm
*Myzus ceraki (black cherry aphid) Tart Cherry
*Myzus persicae (green peach aphid) Peach, apricot, other Prunus
Nasonovia aquilegiae (columbine aphid) Columbine
Nearctaphis bakeri (shortbeaked clover aphid) Hawthorn
Periphyllus lyropictus (Norway maple aphid) Norway maple
Prociphilus fagi (woolly beech aphid) Beech
Pterocomma bicolor Populus
Pterocomma smithiae (black willow aphid) Willow
Rhopalosiphum cerasifoliae (chokecherry aphid) Chokecherry, pin cherry
Rhopalosiphum nymphaeae (water lily aphid) Prunus, various aquatic plants
Thecabius lysimachiae (moneywort aphid) Black poplar, moneywort (Lysimachia)
Tuberolachnus salignus (Giant willow aphid) Willow
Uroleucon sp. Many flowers

Life History and Habits

Aphids are small insects that may be found on leaves, stems and sometimes branches of plants. They have an oval body form and a pair of pipe-like structures (cornicles) usually can be seen protruding from the back of the body. Colors are widely variable among the different aphid species – ranging from very pale yellow to dark, nearly black. Most have shades of green or orange and a few species are even bright red. Upon close inspection, many aphids can be seen to have intricate body patterning. All aphids are small, ranging from 1.5-5.0mm, with the larger species found on stems and branches.

Figure 3: Honeydew produced by aphids covering oak leaves. Photograph courtesy of Jim Kalisch, University of Nebraska.

Figure 4: Sooty mold growing on a wall and walkway underneath a linden tree that is chronically infested with linden aphid.

Figure 5: Yellowjacket wasp feeding on honeydew produced by linden aphid.

Some aphids obscure their body by covering themselves with waxy threads. These are known as “woolly aphids.” The woolly apple aphid is a common woolly aphid that clusters on the limbs of apples and crabapples. Aphids that cluster within leaves that curl, such as the leafcurl ash aphid, are wax covered as are most aphids that live on plant roots. On conifers a related group of insects occur, the adelgids, which similarly cover themselves with waxy threads.

Figure 6: Giant willow aphids that develop on willow stems are the largest aphids found in Colorado. Photograph courtesy of Jim Kalisch, University of Nebraska.

Figure 7: Colony of aphids on the leaves of willow.

Colonies of aphids often consist of a mixture of winged and wingless forms. The great majority of aphids usually develop into the wingless form to remain and reproduce on the plant. More winged forms tend to be produced when colonies get overcrowded, plants decline in quality, or environmental cues favor dispersal to new plants.

Essentially all aphids, regardless of their form, are females. Males, if they do occur, are present only in late summer/early autumn, during the last outdoor generation. The normal habit of aphids is for a female to give live birth to a genetically identical daughter aphid through asexual reproduction (parthenogenesis). The newly born aphid can develop rapidly, typically becoming full-grown in about 10 to14 days. Adults usually can produce three to five young per day over the course of their lifetime, which may extend to about a month but is usually shortened by natural enemy activities.

There is a shift in the life cycle of aphids to handle the challenge of winter, when plants are not active and cold temperatures would be lethal. At the end of the summer, different forms of aphids are produced, including special sexual form males and females.After mating, these females can lay eggs, with they typically lay eggs in crevices around buds or on stems. This egg is the stage that the aphid normally survives winter during outdoor conditions in Colorado. Eggs hatch the following spring, shortly after bud break, and the normal life cycle resumes.

Some aphids have even more complicated life cycles that involve alternating among host plants. With these species, eggs are laid at the end of the growing season on a tree or shrub (winter host). The eggs hatch on this plant in the spring and the aphids have several generations on this plant. Later, all winged forms are produced and the leave the winter host and move to feed on a different kind of plant (summer host). The summer hosts of these plants include several garden plants and weeds. Some of the more common aphids that have host alternation in Colorado are listed in Table 2.

Table 2: Some common Colorado aphids that alternate between woody and herbaceous hosts.

Aphid Overwintering Host Summer host
Black cherry aphid Woolly elm aphid Wild mustards
Currant aphid Currant Wild mustards
Green peach aphid Peach, plum, apricot Peppers, cabbage, potato, many garden plants
Leafcurl plum aphid Plum Various aster-family plants,
clover, vinca, thistle
Mealy plum aphid Plum Cattail, reeds
Potato aphid Rose Potatoes, tomatoes and many
other garden plants
Rosy apple aphid Apple, pear, mountain-ash Plantain
Shortbeaked clover aphid Hawthorn Legumes
Sunflower aphid Dogwood Sunflower, yucca, parsley,
cilantro, pigweed, many other
herbaceous plants
Thecabius lysimachiae Black poplar Moneywort (Lysimachia)
Water lily aphid Plum, other Prunus Water lily and many other
aquatic plants
Willow-carrot aphid Willow Carrot, parsley, dill
Woolly elm aphid American elm Serviceberry (roots)

Management

Natural Enemies

Figure 8: Leafcurl ash aphids, a type of woolly aphid. These aphids curl the leaves of green ash.

Figure 9: Aphid on cottonwood giving live birth to a daughter aphid.

Figure 10: Winged and wingless forms of the green peach aphid.

Figure 11. Eggs of the Norway maple aphid tucked around the base of buds. Photograph courtesy of Ken Gray Collection, Oregon State University.

Figure 12a-b: Adult (a) and larva (b) of a lady beetle.

Figure 13a-b: Larvae of a green lacewing (as) and a flower fly (b).

Figure 14: Adult of a parasitoid wasp next to two aphid mummies.

Aphids are quite defenseless and there are numerous insects that feed on them (Fact sheet 5.550, Beneficial Insects and Other Arthropods). The best known of these natural enemies are lady beetles, with lady beetle larvae being particularly voracious predators of aphids. Other common aphid predators include the larvae of green lacewings and flower (syrphid) flies.

Several species of minute stingless wasps parasitize aphids. These parasitoid wasps insert their eggs into the body of the aphid and the larvae consume it internally. Aphids that have been killed by parasitoid wasps (“aphid mummies”) have a conspicuous appearance, becoming bloated, turning light brown or black and sticking to the plant.

Physical and Cultural Controls

On shrubs and garden plants, aphids can sometimes be managed by simply washing them off of plants with a forceful jet of water. Hosing plants may lethally injure aphids and very few surviving aphids that are knocked to the ground can successfully find their way back onto their host plant.

Some flowers that are perennial, but dieback to the ground in fall, have problems with aphids in the spring. Columbine, lupines and perennial asters are examples. With these plants the eggs of the aphids are laid on the leaves and stems in fall. The eggs hatch in spring and if new growth has emerged at that time some of the newly hatched aphids can make it to the growing plant. This can be prevented by removing the old top growth that contains the eggs before plants emerge in spring. This plant material can then be safely composted or piled elsewhere as any aphids that hatch from the eggs will only be able to move very short distances (inches) before dying.

Chemical Controls

Where high numbers of aphids regularly occur and injure plants or outbreaks are not sufficiently controlled by biological controls, insecticides can be used to manage aphids. These are used in several ways.

Dormant Season Oil Applications. Horticultural oils (Fact sheet 5.569, Insect Control: Horticultural Oils) have a special place in aphid control, to kill egg stages during the dormant season. Horticultural oils act largely by smothering insects their use for aphid control would require that they cover the eggs, which are the overwintering stage on some kinds of aphids on trees and shrubs. They would be applied as sprays sometime before bud break, during the dormant season.

Most aphids on fruit trees, aspen/poplars, willows, poplars, pines, rose, lindens, maples, oaks, hawthorn and viburnum survive winter as eggs on the plant and can be controlled with horticultural oils. Other aphids, such as the leafcurling aphids on ash, do not survive winter in this stage and cannot be controlled with horticultural oils.

Non-persistent Contact Insecticide Sprays. Insecticidal soaps and pyrethrins are two commonly available and popular insecticides that can be used to control aphids. Neither of these persists for long (minutes to hours) on the foliage. Only insects that are covered with sprays during application can be killed with these types of products. Neither will move systemically in the plant and they cannot control aphids that have curled leaves and cannot be reached with sprays.

A main advantage of both insecticidal soaps and pyrethrins is that they are selective in their effects, posing minimal hazard to beneficial insects (e.g. pollinators, natural enemies of pests) and have very low toxicity to mammals and birds.

Persistent Contact Insecticide Sprays. Many of the insecticides sold at retail stores will persist for awhile in their ability to kill aphids – and other insects. Some may be able to continue to kill insects for several hours, some for several days.

Most of these types of insecticides found on for sale to control aphids are some type of pyrethroid insecticide. (Pyrethroids are synthetic derivatives of the natural product pyrethrins, which is extracted from flowers of the pyrethrum daisy/Dalmatian daisy.) Pyrethroids can be identified by looking at the active ingredients. Those that end in “thrin” are some pyrethroid: bifenthrin, cypermethrin, cyhalothrin, cyfluthrin, permethrin. None of these move systemically in the plant so they are not effective for aphids present in curled leaves. Malathion is another insecticide that can kill aphids on contact, although its availability is diminishing.

Because of their persistence these insecticides may give better initial control of aphids than a non-persistent insecticide. However, they can have serious effects on the natural enemies of aphids, which may diminish longer term control. Persistent insecticides cannot be applied to plants that are in bloom and being visited by bees.

Systemic Insecticide Sprays. A few types of insecticides have the ability to move into the plant and move systemically. Because of this mobility these systemic insecticides can provide better plant coverage and often provide better control of aphids than do non-systemic insecticides. Systemic insecticides are also able to kill aphids that are protected within a leaf they have curled. Acetamiprid and imidacloprid are the active ingredients of systemic insecticides gardeners can purchase and use as spray. Both may continue to kill insects for a couple of days to a couple of weeks after application.

Sprays of systemic insecticides come with the same limitations as the non-systemic persistent insecticides mentioned above – they may kill natural enemies of aphids and pose risks to pollinators if applied to plants in bloom.

Soil-Applied Systemic Insecticides. The systemic insecticide imidacloprid can be applied to the soil where it may be picked up by plant roots then moved through the plant, concentrating in the newer leaves. This insecticide is widely available at retail and sold under several different trade names. In some formulations used on trees it is combined with a second systemic insecticide, chlothianidan.

These insecticides are normally mixed with water, then poured around the base of the plant. If mulch is present over the treated area, that must be removed before application, but can then be replaced. After application the soil needs to be kept a bit moist to allow the insecticide to move to and be absorbed by roots. There will be some delay between the time of application and when insects will be killed by a soil application of imidacloprid. Normally this will take a couple of weeks if conditions are suitable for root uptake (warm temperatures, moist soil).

Once the insecticide has moved within the plant these treatments will usually be able to kill aphids – and other susceptible insects – for several weeks, perhaps a couple of months. This long persistence can provide very good aphid control. However, it also can increase potential to harm beneficial insects. At particular risk are insects that feed on pollen and nectar, such as bees and some insect natural enemies, since imidacloprid can occur in pollen and nectar. To prevent injury to pollinators, soil-applied systemic insecticides should not be applied to plants that are flowering or soon will be flowering.

1Colorado State University Extension entomologist and professor, bioagricultural sciences and pest management. 4/96. Revised 1/19.

Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating. Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.

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(Answer)

You don’t mention seeing any aphids, themselves. They would be highly visible if present, clustered on the soft tissues. If they are present, the easiest control methods are mechanical: simply squish them with your gloved fingers and/or knock them off with a strong blast of water from a hose. Inspect your tree from time to time and repeat as necessary.

If not aphids, it will be difficult to diagnose your problem and suggest a solution without seeing your tree. However, here are a couple of possibilities to investigate:

Are the ants all over the tree, or only on certain branches? As this is a maple tree, which produces a sweet sap, one possibility for the sticky substance (and ants) might be sap over-production encouraged by the full-west location on a hot day. Or, if the activity is restricted to only certain branches, could there have been slight damage to a branch, or pruning at the wrong time, opening it to leaking sap? If this sounds like your problem, you can hose down your tree to wash off or dilute sap. Japanese maples tend to bleed from cut or damaged tissues and should only be pruned either while dormant in winter or during midsummer, when sap isn’t running.

Another possibility might be scale, a sucking insect which can be harder to see than aphids. Ants are also drawn to areas where scale feeds. Scale insects get their name from the hard, waxy or sometimes fluffy shells they produce to protect the eggs and female. The scale larvae, called crawlers, can be quite small and move along young branches to feed through thinner bark (such as where twigs branch off) or on leaves.

Inspect the trunk and older branches of your maple, away from these feeding areas, looking for the small, shell-like bumps. Depending on the scale species, these bumps might be round or elongated like an oyster shell or even cottony. If you see anything suspicious like that, try to crush or gently scrape one off with a fingernail. This will confirm a scale problem.

Areas in the U.S. are also reporting a newer species of scale specific to Japanese maples. If scale is your problem, controlling it could be tricky – Japanese maples are said to be sensitive to horticultural oil sprays which are the usual treatment. However, the University of Tennessee suggests that lighter, more refined oils (called summer oils) might be appropriate to use. The insecticides mentioned in this last sheet, on the other hand, are banned for cosmetic use in Ontario.

Check back with us once you’ve had a closer look at your tree and let us know if you have further questions. Good luck!

An insect that damages leaves and produces honeydew

Aphids are one of the most common insects found on trees and shrubs. There are over 400 species of aphids that feed on numerous hosts. Aphids use their piercing-sucking mouthparts to extract sap from the tender new growth of plants. Aphids excrete a sticky substance called honeydew that can be a nuisance when it gets on sidewalks, vehicles and other structures.

Infested trees and shrubs can be readily treated
Most shrubs and trees are susceptible to aphids and can be treated with a systemic or topical insecticide. The insect rarely kills its host but can cause unsightly leaf deformation and reduce overall health.

What to look for
• Curled, stunted, wilted, or discolored leaves.
• Plant sap excreted as honeydew making the plant sticky.
• A black fungus called sooty mold may be growing on the honeydew.
• Spots of sap on cars, sidewalks, houses, etc.

Treatment and Prevention
• Plant flowers to provide nectar sources for aphid predators & parasites: lady beetles, green lacewings, hover flies, and parasitic wasps.
• Do not treat unless natural sources of control are not working.
• Aphids can be controlled by both systemic and topical insecticides.
• Insecticidal soap sprays are a “green” option for aphid control.
• Treatment should occur when it becomes an aesthetic nuisance to the landscape or reduces the overall health of the tree.

Contact Aspen Arboriculture today to learn more about the insects that are damaging your shrubs, plants and trees! Serving the Sioux Falls, South Dakota and surrounding areas.

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Sometimes I assume that, given our dry and cool environment, I have seen the vast majority of pest and disease issues in the area. I seem to know when the questions about aspens will arrive:

Early summer: “What is the orange liquid coming out of the trunk?” Answer: could be Cytospora canker. Usually doesn’t end well.

Mid-summer: “How do I get rid of all these aspen shoots coming up in my lawn?” Answer: You won’t. Moving would solve the problem.

Late-summer: “All the leaves on my aspens get this black spot, and the leaves fall off. Is my tree dying?” Answer: It probably is, because it’s an aspen tree, but the fungal disease, Marssonina leaf spot, is the cause. Rake up your leaves in the fall and discard them.

Similarly, I tend to know when the questions about the lawn going brown (mid-July), the powdery substance on the leaves of the squash plant (August) or the worms in apples (October) will start coming in.

But this year has been different. Way different. All that rain (4-6 inches, depending on location) and snow, followed by two weeks of temperatures near 90 has created the ideal conditions for diseases and insects. And by ideal, I mean the “perfect storm.”

During the past seven years, I have never seen aphids this bad. Leaf-curling plum aphids (fruit trees), black cherry aphids (tart cherries), green peach aphids (peaches, apricots and most vegetables), cabbage aphids (cole crops, including, you guessed it, cabbage) and pea aphids, most commonly found on, you guessed it, alfalfa.

At this point in the season, if the insects haven’t curled the leaves yet, you can always try a forceful jet of water to wash them off. If the aphids lose a leg, or get displaced to the ground, the odds of them getting back on the plant are slim. Other than that, there really isn’t much you can do about controlling them. But as my friend Courtney does, cut out this article, stick it in a drawer and save it for next winter, because that’s when you can start the control of the upcoming invasion.

On trees and shrubs that get hammered by aphids, try applying a horticultural oil during the dormant season. The best time would be late February through early April before bud break. The oils, a highly-refined petroleum product, are applied to the trunk and branches, smothering the eggs and overwintering females.

If you see aphids during the season, and the hose isn’t doing the job, try insecticidal soaps and oils, focusing on the undersides of the leaf. The nice thing about these products is they leave no toxic residue, so they don’t kill natural enemies that migrate in after the spray.

Lastly, and maybe most importantly, use flowering plants in your landscape, as the nectar and pollen are valuable food sources for the adult stages of beneficial insects, such as lady beetles, green lacewings and syrphid flies. Their larval stages are voracious consumers of aphids – much more than when they are adults – and could end up being the most effective form of aphid control in the garden.

Darrin Parmenter is the director and horticulture agent of the La Plata County Extension Office. Reach him at [email protected]

Chaitophorus tremulae

Identification & Distribution:

Chaitophorus tremulae apterae are elongate oval with the dorsum solidly blackish sclerotic, rather densely sculptured with denticular spinules, and very often with a paler line along the mid-dorsum (see first picture below). Except in the fundatrix, abdominal tergite 1 is more or less completely fused with the carapace on tergites 2-6. The antennae are usually dark and half the length of the body, and the terminal process is 2.1-2.8 times as long as the base of the last antennal segment. The siphunculi are dark and the legs are brown with the hind pair darker. The body length of Chaitophorus tremulae is 1.2-2.5 mm.

Alates have very broad black dorsal abdominal cross-bands which tend to coalesce. Immature Chaitophorus tremulae are bright green.

Aspen leaf aphids live in small colonies on undersides of leaves of Aspen (Populus tremula) and a few related species of Populus (Populus canescens, Populus davidiana, Populus gracilis, Populus laurifolia, Populus maximowiczii, Populus sieboldii, Populus simonii, Populus suaveolens). They have also been found in leaves spun together by other insects, or in leaf-nest galls made by another group of aphids (Pemphiginae). Oviparae and alate males occur in October. Chaitophorus tremulae occurs throughout Europe and as subspecies in the Far East.

Biology & Ecology:

In Britain Stroyan (1977) describes Chaitophorus tremulae as being locally common which is also our experience. We have found it in most woodlands where aspen is common, sometimes as quite large colonies.

One feature of the picture of the alate above is the large droplet of honeydew. You can also see some smaller globules of honeydew on the leaves in some of the other pictures.

With some species the honeydew would be avidly consumed by attending ants. But honeydew of Chaitophorus tremulae has a much lower content of the sugar melizitose (Fischer & Shingleton, 2001) and is not very attractive to ants.

The colony below consisted largely of apterous adults with very few nymphs present. Although not reported elsewhere, perhaps they have a period of reproductive diapause in mid-summer.

Chaitophorus tremulae was recorded from Wales for the first time by Baker & Broad (2009). They found that the common garden ant Lasius niger ignored Chaitophorus tremulae when attending Chaitophorus populeti feeding at the same time on the same leaves. In contrast Novgorodova (2005) records Lasius fuliginosus and Myrmica rubra as attending Chaitophorus tremulae. So far none of the colonies we have found has been attended by ants.

Other aphids on same host:

Blackman & Eastop list 17 species of aphid as feeding on European aspen (Populus tremula) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 11 as occurring in Britain (Show British list).

Damage and control

Aspen is grown commercially for its wood which has a number of uses. We know of no studies that have examined the impact of aspen leaf aphid on tree growth, but its usual low numbers would make it unlikely to affect tree growth.

Acknowledgements

Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

Useful weblinks

Leafcurl ash aphid

Description of leafcurl ash aphid

The leafcurl ash aphid (Prociphilus fraxinifolii) is a consistent pest of green ash trees. Leafcurl ash aphids are small light-green insects covered with off-white waxy threads. They remain on the underside of the leaves, inside the curled leaves. Biological controls, especially syrphid fly larvae and lady beetle larvae are often abundant among the aphids.

Damage caused by leafcurl ash aphid

Presence of the aphids on the undersides of the foliage causes a distinctive gnarled deformation at the ends of the twigs. The clusters of tightly coiled leaflets are noticeable throughout the second half of the summer. Damage is annoying and aesthetically displeasing but has no significant impact on otherwise healthy trees.

Damage occurs only on new growth that emerges after the aphids arrive in mid to late May. Expanded leaves are not susceptible to leaf curling. Consequently, the damage remains confined to a very limited proportion of the tree’s total foliage.

Management of leafcurl ash aphid

Spraying insecticides is generally not warranted for this problem. By the time damage is apparent it is too late for effective treatment. Spraying would have to precede deformation, as curled leaves will not return to normal even if the aphids are killed. Damage is aesthetic and of no consequence on healthy, well-established trees and spraying will be harmful to biological controls. If preventive chemical treatment can be justified use a foliar systemic insecticide such as Orthene or Dimethoate.

As a practical consideration, prune off and discard the deformed terminals that can be reached and ignore the rest.

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Please see our website for current forms, fees, and instructions on preserving and mailing insects.

Contact information for each states diagnostic laboratory for U.S. residents. If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic

North Dakota State University

Ash leaf curl aphids (Figure 1) are common on urban trees (ash) in Fargo and other cities (Beulah in Mercer County), possibly due to the warm winter. Ash leaf curl aphids are woolly aphids (<1/8 inch) that produce white waxy threads that cover their bodies (hence the name “woolly aphids”). Aphids feed on the plant juices on the underside of leaves causing leaves to curl and become deformed (Figure 2). Natural enemies (lady beetles, green lacewings, syrphid flies and small parasitic wasps) do a great job controlling aphids most years. However, aphid populations can explode quickly due to their rapid reproductive rate and short life cycle. In those situations, using a strong stream of water under high pressure can wash and drown aphids on small to medium size trees. Larger trees can usually tolerate aphid infestations unless stressed from drought or other factors. Keep trees healthy by watering in hot and dry conditions. If insecticides are necessary, insecticidal soap, horticultural oil, neem insecticide and insecticides such as Orthene (active ingredient acephate) are recommended as foliar insecticides. The systemic imidacloprid soil drenches applied in the root zone also can reduce aphid populations, but are slower to work and it can take up to a month or more to see results on larger trees.

Janet J. Knodel

Extension Entomologist

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