House Plant Pests

 

Aphids are small insects, usually green or black, that suck the plant juices out of new growth or flower buds. Sprays containing botanical insecticides such as pyrethrin or insecticidal soap will kill aphids on contact. Repeated spray applications are necessary. Plants infested with aphids will have to be watched closely for some time. If aphids are only a problem on the flower buds, which often happens on hibiscus, remove all buds at the same time to eliminate the aphids.

 

Mealy Bugs are small, flat grayish-white insects that form clumps of damp wool-like cocoons. Mealy bugs are most often found in crotches where leaves join stems or where stems meet. These insects can be killed on contact with a botanical insecticide such as pyrethrin or insecticidal soap. Even with this treatment, plants will have to be watched very carefully for several months. Rather than spraying the whole plant only spray specific insects or cocoons or dab them with a cotton swab that has been dipped in a 50% water:rubbing alcohol solution Mealy bugs can attack almost any plant but prefer succulent plants like hoya, jade, and cacti.

 

Spider Mites are almost too small to see. Plants infested with spider mites will demonstrate tiny white specks on the underside of their leaves, especially near leaf mid-ribs. Later, fine silky webs are formed which are most obvious if plants are misted with water. Spider mites feed by sucking sap from the plant tissue causing a speckled leaf appearance. Spider mites are actually spiders, not true insects, so a specific mite killer is effective at killing them. Spray the undersides of the leaves with insecticide twice a week for a month . Mist the plant with a strong spray of water before spraying as spider mites do not like moist, humid conditions.

 

Fungus Gnats often mistaken for fruit flies, a fungus gnat infestation will most often be noticed in their adult form as tiny black flies hovering near overwatered plants. The adult flies lay their eggs in the soil which eventually hatch into tiny white maggots. These maggots can only damage healthy roots if they are present in massive numbers. Their main food source consists of dead, rotting roots and other decaying material like peat moss or fungus in the soil. Fungus gnats rarely kill plants. In fact, the plants they are infesting are most likely dying from overwatering or poor drainage. As a result of the excess moisture, the fine absorbent roots decay, supplying the gnat larvae with a source of food. To eliminate these pests water less if possible. Allow the top inch or so of soil to dry out as this is where the majority of larvae live. If this is ineffective, apply rotenone every few weeks to eliminate the population over time. Another method is to introduce Hypoaspis mites which attack fungus gnats.

 

Scale can look like drops of dried glue on stems or leaves. Plants with scale are best destroyed as chemical treatments are only a temporary measure. Scale spreads to other plants if the source is not eliminated. Scale is often mis-identified as leaf spot, sun burn, or a fungal infection. Bring a leaf in for positive identification under a magnifying glass.

 

Thrips are tiny dark, slender active, flying insects that swarm when disturbed. They suck sap from the leaves, causing silvery white streaking or blotching. Thrips are chemically controlled by Trounce or End-All.

 

White Flies are tiny white, moth-like, flying insects which swarm into white clouds when plant leaves are disturbed. They suck sap from primarily the undersides of leaves, causing them to discolor to yellow and then to die. Whiteflies secrete honeydew which favors dark fungal growth. Whiteflies overwinter only indoors in houses, but in summer infest outdoor annuals and perennials. They are controlled chemically by pyrethrins.

 

 

Garden Insect Pests

 

Ants do not eat plants or kill them directly. There are 8800 species worldwide, with 580 in North America and 100 species in Canada alone. These insects live in underground nests or in large soil mounds. As these mounds are pushed up plant roots are damaged. The unsightly mounds can smother turf or greatly reduce the vitality of vegetables, annuals, perennials, or even trees and shrubs. Ants are neither beneficial nor harmful to peonies. Water your lawn thoroughly after each treatment. Cultural controls such as digging up the nest or drowning can be very effective. Please see Golden Acre staff for chemical treatments.

 

Aphids are small green, gray, red or black insects with or without wings that attack almost any type of plant by sucking sap from leave or stems. The damage caused by aphids appears as stunted and curled new growth and is usually associated with the presence of a sticky shiny substance called honeydew. Aphids commonly attack honeysuckle, dogwood, mayday, elm, and apple trees. A sooty black mold often develops on plant tissue coated with honeydew. Control aphids with foliar applications of Ambush, insecticidal soap, or Trounce. A steady spray of water from the garden hose can dislodge the insects.

 

Cabbage Worms are green caterpillars which chew holes in the leaves of cabbage, cauliflower, broccoli, and brussels sprouts (cole crops). Control cabbage worms with repeated applications of Rotenone or BTK. Row covers stop butterflies from laying eggs on plants.

 

Caterpillars: This broad family of insects appear in most any color from yellow to black. Caterpillars cause damage to many different plants by actually chewing away large sections of leaf tissue. Most caterpillars are somewhat particular which type of plants they will feed on. Control caterpillars on food crops with pyrethrins or Rotenone dust. Contact chemicals such as Ambush will eliminate caterpillars from feeding on ornamental plants. Green leaf rollers are caterpillars that roll themselves in leaves and webbing. Leaf roller caterpillars can not be contacted with chemicals. Caterpillars are best controlled by manual removal or through BTK when they are very small.

 

Cutworms are green caterpillars with black heads. These caterpillars cut beans, peas, and many other tender young plants off at ground level. When touched, cutworms will always curl into a tight ball. Control cutworms by applying Rotenone to the soil prior to planting ornamental flowers. BTK may be effective when they are small. Other controls like placing barriers around the young seedlings can also work.

 

Flea Beetles are small shiny black or dark red beetles which attack almost any vegetable crop. They leave many small pinholes in the leaves. Flea beetles jump when disturbed. Control flea beetles with applications of Rotenone, insecticidal soap, or Trounce. Spray flea beetle infested plants twice weekly until the insects are under control.

 

Maggots are small white worm-like insects that attack vegetable crops such as cabbage, cauliflower, broccoli, brussels sprouts, radishes, carrots and onions. Prevention is the best cure for maggots.

Slugs (shell-less snails), are usually dark brown slimy creatures that attack almost any vegetation. Place Safer's Slug and Snail Bait (a new product consisting of ferric phosphate and perfectly safe for humans and animals) in a cool moist place where slugs hide during the day. These spots can be located by following, early in the morning, the slimy trails that slugs leave as they move. Keep soil free of mulch and dead plant material as these are ideal places for slugs to hide. Water in the morning, not in the evening, because they move less easily on dry soil. Cover soil surface with sharp sand to prevent slugs from moving around on soil surface.

 

Spider Mites are minute sap sucking pests that cause plant foliage to yellow, brown, and eventually dry up and drop. They are common on almost every type of plant including house plants (see House Plant Pests), deciduous and evergreen trees and shrubs, perennials, and annuals. Damage appears as spotted leaves or needles and dead patches in spruce or pyramidal junipers. A fine webbing is usually present which is often noticed after a rain. Spider mites are more common during hot dry weather than during cool damp weather. Control spider mite infestations on outdoor ornamentals with two applications, about a week apart, of Ambush. By hosing spider mite infested trees down once a week you can provide some natural control because they can not fly and may not climb back up into the tree.

 

 

Deciduous Tree and Shrub Insects

 

Birch Leaf Miner: The larvae of these insects tunnel or mine into the leaf tissue creating unsightly brown patches on the leaves. These areas can be pulled apart to reveal tiny larvae between the leaf layers. When damage is noticed, contact insecticides are not effective since larvae are safely hidden within the leaf tissue. Systemic pesticides were effective but are no longer available. Try to deal with the adult females as they lay eggs. Spray the foliage with Ambush, a synthetic pyrethroid, when the leaves are fully opened and repeat in mid-June and again in early July. Remember, birch and other trees under drought stress are prone to insect attack. Keep your birch deeply watered out to and beyond the dripline. If possible, also mulch this area to conserve soil moisture.

 

Cottony Ash Psyllid The nymph stage of this insect pierce leaf tissue, feed on plant juices and inject a toxin causing severely curled or "cauliflowered" leaves and leaf drop. It is a new insect to our area which attacks black and Manchurian ash trees. During summer, the feeding nymphs are covered in "cotton" and enclosed in the leaf. Spraying has little effect at this time, therefore it is best to spray the newly-hatched nymphs with Trounce (pyrethrin; insecticidal soap) just when leaf buds start to open, usually in late May or early June. Spraying again about one month later is less effective but may kill some of the second generation nymphs as they hatch in late July/early August.

 

Pear Slugs are the larvae of a sawfly species and appear as small dark slugs on the surface of plant leaves. Pear slugs skeletonize leaves as they scrape away upper leaf surfaces. They are common on Cotoneaster hedges, and Hawthorns. There are generally two generations of pear slugs during the growing season. The second generation which appears in August does the most leaf damage. Since these insects attack plants in the season they don’t do any measurable harm to the shrub. Earlier infestations of pear slug can be effectively controlled with spray applications of Ambush/permethrin.

 

Ash Bark Beetles have recently become a major problem on green, black, and Manchurian ash trees. Mountain ash, which are in the rose family, are unaffected by these insects. Trees infected with the larvae of ash bark beetles will show signs of wilted leaves and later dead branches will be evident throughout the crown area. Where dead and live branches meet you will see circular rings of tiny holes. Cut open the bark to reveal tunnels, called galleries, that restrict sap flow and disrupt plant growth beyond these rings.

 

Control: As soon as you notice these rings of beetle entry holes, prune damaged branches back beyond the damaged area; make cuts just above the nearest healthy branch or leaf cluster. The damaged branch portions that have been removed should be sealed with plastic bags to prevent the emergence of the beetles and their re-entry into other ash trees. If beetle infested trees are not pruned the beetles will emerge from the tunnels in late July to mid August. From here they travel down tree trunks and burrow into the bark close to tree bases. There are no available systemics and foliar sprays are not effective.