“Pests, Pests & More Pests”
by Duane Farmen
Several years ago Dr. Art Antonelli published a list of the 30 most common pests that every Master Gardener should know. We recently were advised that this list was still appropriate. With that in mind, over the next few months a brief discussion will be provided on those pests. In addition, the related reference materials that discuss control and management of these pests will be included.
The pests to be discussed in this issue are: Aphids; Scales; Tent Caterpillars; Root Weevils; Slugs and the European Cranefly.
Adelgids - aphids – Insect Order of Homoptera’
These are piercing-sucking insects and cause damage to a variety of plants. There are several species, 5 which are common and attack ornamental plants:
Note:
There is also reference to Aphids in EB1229 Rhody & Azalea Problems p17.
Scales – Insect Order of ‘Homoptera’
These are piercing-sucking pests that feed on plant juices of a variety of host plants, which include fruit trees, small fruits, dogwood, maple, roses, and cherry laurel. Damage usually results in stunting and/or wilting. The most frequent problem is the unsightliness, which results from sticky, sweet honeydew that scales excrete. The excretion can proliferate the growth of black sooty mold.
As with the Aphids there are several species. Most common in our area are:
Tent Caterpillars – Insect Order of Lepidoptera
There are two kinds of tent caterpillars in Washington; Forest tent caterpillar and the more numerous Western tent caterpillar, which is the species discussed here. It has orange and black markings and spins tents on the tips of branches of deciduous trees in the spring. The larvae feed on the leaves resulting in defoliation. The plant normally survives even serious infestations, unless it is under stress from other problems.
Refer to EB1106, EB1229 Rhody & Azalea Problems p2 and EB 0826 p54.
Root Weevils – Insect Order of Coleoptera
These are chewing insects. Their presence is identified by the marginal notching of the leaves. This is the most important insect pest of rhododendrons and azaleas. They are several species of the root weevil with only 3 of primary importance; obscure root weevil,
black vine root weevil and the woods weevil. Their coloration varies by species but usually brown or black with flecks of yellow, white or gray. The larvae can cause root injury, while the adults feed on the leaves.In some instances, they feed on the bark and can cause girdling of the plant trunk.
Refer to EB0970, EB0826 p53 and PNW Landscape IPM Manual p127, 128.
Slugs – ‘Gastropod’ – Order of Stylomatophora
There are several slug species in Washington. The most common are the gray garden slug and European slug. However, the only
slug native to our area is the Banana slug, which prefers wooded areas. Slugs are soft-bodied animals, without a backbone, that move on a muscular foot over a mucous trail. They are a “rasping” pest that feeds primarily on young plants. They are not considered a “chewing” pest. The obvious sign of their presence is the slime trail that appears silver when dry.
Refer to EB0968, Q&A 92, EB0826 p53 and “Sustainable Gardening” (refer to page 520 of the index for all references).
European Crane Fly – Insect Order of Diptera
This is largely a turf and pasture pest. The adult looks like a large mosquito with a body about one inch long. The adult females lay their eggs in the grass, which hatch into small, gray, tough-skin larvae. Thlarvae feed on the grass roots through the winter, hatching into adults in late summer and early fall.
Refer to EB0856, EB0482 Home Lawns p14 and “Sustainable Gardening” p277-280.
Several years ago Dr. Art Antonelli published a list of the 30 most common pests that every Master Gardener should know. We recently were advised that this list was still appropriate. With that in mind, over the next few months a brief discussion will be provided on those pests. In addition, the related reference materials that discuss control and management of these pests will be included.
The pests to be discussed in this issue are: Aphids; Scales; Tent Caterpillars; Root Weevils; Slugs and the European Cranefly.
Adelgids - aphids – Insect Order of Homoptera’
These are piercing-sucking insects and cause damage to a variety of plants. There are several species, 5 which are common and attack ornamental plants:
- Balsam Woolly Adelgid – These appear as white, woolly masses or dirty white encrustations on the trunk and limbs on true firs. On terminals they cause a swelling making twigs appear to end in solid knobs. Infestations weaken the tree, thin foliage and may cause death of the tree. Refer to EB0826p22 (see Firs) and PNW Landscape IPM Manual p161.
- Cooley Spruce Gall Adelgid – This “aphid” alternates between spruce and Douglas fir. On Douglas fir they appear as white cottony masses on needles causing yellowing and needle distortion. On spruce the plant responds to the feeding insect by forming a cone-shaped gall around the adelgids. Galls can be green or purplish, then turn brown and dry. Refer to EB0966 and the PNW Landscape IPM Manual p33 & 153.
- Pine Bark Adelgid – The infestation appears as tiny, woolly clumps on the trunk, branches & twigs. The woolly clumps are the adelgids covered by waxy material, which they exude. These insects feed on the surface of the bark. Refer to EB0826 p37 and PNW Landscape IPM Manual p111, 112.
- Spruce Aphid – This winter aphid is a dull green. It causes severe needle drop to spruce trees during spring and summer.Symptoms of infestation are yellow blotches on the needles and most commonly occur on lower, inner foliage of the tree. This insect injects a killing toxin into the needle. Refer to EB1053, EB0826 p45 and the PNW Landscape IPM Manual
p154. - Rose Aphid – These are most commonly known to attack the new growth on roses. They cause chlorosis, may have a toxin that kills leaf tissue and excrete a honeydew that can lead to sooty mold. Refer to the PNW Landscape IPM Manual p138,139, EB0826 p41 and Fact Sheet #13.
- Hemlock Woolly Adelgid – These are small insects, generally brownish-reddish in color, oval shaped and about 0.8mm long. Both the immature nymphs and adults damage trees by sucking sap from the twigs. The tree loses vigor and prematurely drops its needles to a point of defoliation. Evidence of this insect is the presence of dirty white, globular masses of woolly puffs attached to the twigs or base of the needles. In our area, this pest is found mostly on hemlock hedges. Refer to EB0826 p25 (see “hemlock chermes”).
Note:
There is also reference to Aphids in EB1229 Rhody & Azalea Problems p17.
Scales – Insect Order of ‘Homoptera’
These are piercing-sucking pests that feed on plant juices of a variety of host plants, which include fruit trees, small fruits, dogwood, maple, roses, and cherry laurel. Damage usually results in stunting and/or wilting. The most frequent problem is the unsightliness, which results from sticky, sweet honeydew that scales excrete. The excretion can proliferate the growth of black sooty mold.
As with the Aphids there are several species. Most common in our area are:
- Lecanium Scale – There are many species ranging from mottled to a shiny brown. They are turtle-shaped and cluster in large numbers on small branches at leaf axils, nodes or fruit spurs. The plant loses vigor, leaves are smaller or do not form. They feed on a large variety of trees & shrubs. Refer to EB0746, EB0826 p32, EB1552 p8, and the PNW Landscape IPM Manual
pages 29-31. - Soft Camellia Scale - Also known as the “brown soft scale”,this is a very small insect (1/8 –3/16” in length) oval, flattened, soft shell, green-brown in color. In the crawler stage they are a yellow-brown. When abundant, their presence is noted by a sooty mold. They feed on the undersurface of the leaf, especially camellia, holly and daphne. However, they are also a pest of greenhouse ornamentals and houseplants. Refer to EB0826 p50 and EB1552 p13.
- Pine Needle Scale - These are elongated, flat, white scales that appear on leaves. Heavy infestation can cause severe damage. Host plants are primarily pines, occasionally Douglas fir, spruce and cedar. Damage is evident from a weakening of the plant, slow growth, foliage becomes yellowish and in heavy infestations foliage appears white. Refer to EB1552 p7, EB0826 p37 and PNW Landscape IPM Manual p112.
- Oyster Shell Scale - This scale resembles miniature oysters and is light to dark brown. They live under a shell of wax and form solid crusts on twigs & limbs and may kill the tree. They are found on a large number of broadleaf trees. Refer to EB0826 p32, Em1552 p9 and PNW Landscape IPM Manual p30-31.
Tent Caterpillars – Insect Order of Lepidoptera
There are two kinds of tent caterpillars in Washington; Forest tent caterpillar and the more numerous Western tent caterpillar, which is the species discussed here. It has orange and black markings and spins tents on the tips of branches of deciduous trees in the spring. The larvae feed on the leaves resulting in defoliation. The plant normally survives even serious infestations, unless it is under stress from other problems.
Refer to EB1106, EB1229 Rhody & Azalea Problems p2 and EB 0826 p54.
Root Weevils – Insect Order of Coleoptera
These are chewing insects. Their presence is identified by the marginal notching of the leaves. This is the most important insect pest of rhododendrons and azaleas. They are several species of the root weevil with only 3 of primary importance; obscure root weevil,
black vine root weevil and the woods weevil. Their coloration varies by species but usually brown or black with flecks of yellow, white or gray. The larvae can cause root injury, while the adults feed on the leaves.In some instances, they feed on the bark and can cause girdling of the plant trunk.
Refer to EB0970, EB0826 p53 and PNW Landscape IPM Manual p127, 128.
Slugs – ‘Gastropod’ – Order of Stylomatophora
There are several slug species in Washington. The most common are the gray garden slug and European slug. However, the only
slug native to our area is the Banana slug, which prefers wooded areas. Slugs are soft-bodied animals, without a backbone, that move on a muscular foot over a mucous trail. They are a “rasping” pest that feeds primarily on young plants. They are not considered a “chewing” pest. The obvious sign of their presence is the slime trail that appears silver when dry.
Refer to EB0968, Q&A 92, EB0826 p53 and “Sustainable Gardening” (refer to page 520 of the index for all references).
European Crane Fly – Insect Order of Diptera
This is largely a turf and pasture pest. The adult looks like a large mosquito with a body about one inch long. The adult females lay their eggs in the grass, which hatch into small, gray, tough-skin larvae. Thlarvae feed on the grass roots through the winter, hatching into adults in late summer and early fall.
Refer to EB0856, EB0482 Home Lawns p14 and “Sustainable Gardening” p277-280.