INSECTS
If an insect problem seems likely, it is most helpful to know the type of plant and when the damage occurred (month/season). Insects have varied mouthparts and cause specific damage.
A chewing/rasping insect feeds on plant tissue and can cause ragged/chewed or missing leaves (caterpillars, slugs, beetles, grasshoppers); rolled leaves (leafroller); and tunnels in between upper and lower leaf surfaces (leaf miners). This family of insects can also cause holes in stems, branches or trunk; sections of the tree to die; premature yellowing (wood borers); girdled or dead stems (cutms, twig girdlers, or stem borers); or general decline of plants due to root damage (soil- dwelling insects).
A sucking insect feeds on plant fluids and injects toxins into the plant. The toxins can cause leaf spotting or stippling (aphids, leafhoppers, spider mites); leaf distortion such as curling or puckering–more commonly this can be damage from leafhoppers and thrips–or poisoning of entire plants, resulting in stunted growth and/or yellowing (scale, mealybugs, mites, aphids, whitefly).
Encourage beneficial insects in your landscape by planting what they prefer and avoiding broad spectrum insecticides which kill pests, as well as beneficial insects. Naturally occurring predators and parasites of harmful insects are found in gardens, orchards, and fields. Browse the 2024 Pest Management Guide.
Beneficial Insects and Mites. Many species of beneficial insects and mites can be purchased. Beneficial insects are target specific and require gardener knowledge of existing pests. Timing of release is an important factor and if pests are not present then neighboring gardens may benefit more than your garden. Beneficial insects and mites, in general, have specific requirements for long-term survival and may need to be released anew each season. Learn more about attacting beneficial insects to your yard.
Important Practices
- Reduce insect and pest populations by hand removal and regular clean up
- Learn which insects are common to plants growing in your landscape or garden
- Monitor plants in the landscape regularly to recognize when pests are present
- Maintain healthy plants by meeting their cultural requirements (sun, shade, wet, dry…) with the goal of using no or few pesticides which kill beneficial insects, too
- Establish thresholds for acceptable levels of insect infestation
Provide a sample of an unknown insect to the Help Desk for diagnosis. Mondays and Tuesdays are the best days to bring in samples; hours are 8 am – 5pm at 8033 Ashton Av, Suite 105, Manassas, 20109. Please call (703) 792-7747 or email mastergardener@pwcgov.org before bringing in a plant or insect so that we may make best use of time.
If an insect problem requires chemical controls, contact the Help Desk for more information. Use the least toxic materials according to the label. An Extension agent can help you identify the proper and legal pesticide and its best usage.
Additional Resources
Insect Identification and Diagnosis Request, Virginia Tech is a form for requesting assistance from the Help Desk or State scientists concerning difficult insect problems. Form to request insect Identification.
Garden Insects and Pests, Virginia Tech Publications and Educational Resources provides numerous links to more detailed information on specific insects and pests.
Specific Insects and Solutions
There are numerous insects that have evolved over the years to thrive on ornamental plants, vegetables, fruit trees, woody shrubs, lawn turf, and virtually every botanical species. Do not hesitate to ask for assistance.
While not complete, the following are insects that are commonly diagnosed by our Help Desk volunteers:
Aphids: Aphids are one of the most common spring and early summer insects. Any plant that is curled or puckered should be checked for aphids on the underside of the leaves. While they can distort and stunt growth, and spread diseases, they are often attacked by various predators and parasites before they do any serious damage. Affected leaves can often be pinched off, literally “nipping the problem in the bud”. The number of susceptible plants is numerous. VT Extension APHIDS Publication.
Borers:
- Azalea Stem Borer: Look for tips dying back and yellow legless grubs up to ½ inch long boring in twigs and trunk. Plants susceptible are azalea, rhododendron, mountain-laurel, and blueberry. See http://www.ces.ncsu.edu/depts/ent/notes/O&T/shrubs/ort076e/ort076e.htm
- Bronze Birch Borer: Look for the top of the tree dying back and up to 1-inch-long flat-headed borers under the bark. Plants susceptible are birch, cottonwood, poplar, and aspen. Learn more about the Bronze Birch Borer.
- Rhododendron Borer: Larvae bore in the sapwood just under the bark, causing the branches to wilt and die. Adults are clear-winged moths. Plants susceptible are rhododendron, sometimes azalea, and mountain-laurel. Learn more about the Rhododendron Borer
- Bagworm: Caterpillars form “bags” around their bodies made of silk and plant debris. They overwinter as eggs in the bags; the eggs hatch in late May and early June. Plants susceptible are conifers, maples, sycamores, box-elder, and many others. Talk with an Extension Agent to determine the time of year that caterpillars are most susceptible to chemical controls.
- Tomato hornworms quickly defoliate plants. They are often parasitized by beneficial wasps. Learn more about Tomato Hornworms.
Lace Bugs:
Azalea Lace Bug: Prefers plants in full sun because predators prefer shadier locations. The tops of the affected leaves are stippled, or bleached out by feeding damage, while the leaf bottoms are covered with small dare excrement spots. Typically, damage starts to show up in mid-summer. Plants susceptible are azalea, cotoneaster, and pyracantha. Learn more about Lace Bugs.
Leaf Miners:
- Boxwood leaf miner: Look for yellowed leaves and leaves with small brown spots. Depending on the time of the year, you may see adult yellow flies on the foliage.
- Holly leaf miner: Look for long serpentine or blotch mines in the leaves. Heavily infested leaves turn yellow-brown. Inside the leaves will be small pale larvae. Plants susceptible are native and English holly.
- Learn more about Leaf Miners.
Scale:
Scale insects come in many varieties and are generally plant specific. Proper identification is necessary for optimal control. Learn more about Scale.
- Azalea bark scale: Look for white cottony sacs covering dark red females and eggs on the forks of branches and twigs. Plants susceptible are azalea, blueberry, and rhododendron.
- Juniper scale: Scales have an elongated white covering with a yellow cap at one end. Crawler stage is from June 5-20.
- Maple scale: Look for cottony masses on the undersides of twigs and branches. Foliage on affected branches may turn yellow and the branches may die. Plants susceptible are all maples, locust, white ash, red mulberry, linden boxwood, and many others.
- Wax scale: A globular off-white scale found on the twigs and leaves. This scale is so named because of its waxy color. Plants susceptible are holly, euonymus, pyracantha, boxwood, hemlock, and others.
Squash Bug:
Nymphs are grayish white with dark heads and appendages. Adults are oval elongate, light gray and mottled yellow on the underside. Nymphs tend to be found on the basal portions of the vine. Plants susceptible are squash, pumpkin, cucumber, and melon, in that order. Learn more about Squash Bugs.
Stink Bug: Barrel shaped eggs are laid on the undersides of leaves, nymphs are black and white or red or green. Adults are green or tan. All stages have piercing-sucking mouth parts. Damage to pepper and tomato appears as white halos and deformations on the fruits. Susceptible crop plants are many, especially pepper and tomato. Learn more about Stink Bugs.
Beneficial Insects:
While not complete, the following list of insects are among those beneficial to the garden and landscape. These insects feed on and control the populations of harmful insects. Spot use pesticides should be a last resort since they may kill beneficial insects and allow harmful insects to run rampant.
- Assassin bug – Reduviidaye – The assassin bug feeds mainly on aphids, caterpillars, Colorado potato beetles, Japanese beetles, leafhoppers, and Mexican bean beetles.
- Damsel bug – Nabidae – The damsel bug feeds on aphids, leafhoppers, mites, and caterpillars
- Big-eyed bug – Lygaeidae – Big-eyed bugs feed on aphids, caterpillar eggs and larvae, immature bugs, leafhoppers, and spider mites
- Predacious stink bug – Pentatomidae – Predacious stink bugs feed on Colorado potato beetles and various caterpillar larvae
- Syrphid fly larvae – Syrphidae – Fly larvae of this species feed on aphids and mealybugs
- Lady beetle – Hippodamia convergens – The lady beetle feeds mainly on aphids and other soft- bodied insects, such as mealybugs and spider mites
- Green lacewing larvae – Chrysopa camea – Lacewing larvae, known as aphid lions, feed on insect eggs, aphids, spider mites, thrips, leafhopper nymphs, and small caterpillar larvae. Adult lacewings are not predacious
- Predatory mites – Phytoseiulus persimilus and several other species, feed on many mite pests, including the two-spotted spider mite
- Trichogramma wasp – Trichogrammatidae – This tiny wasp attacks eggs of more than 200 pest species, including cutworms, corn borers, corn earworms, armyworms, codling moths, and cabbage moths. Release time is critical for their effectiveness since they only attack pest eggs.
- Encarsia wasp – Encyrtidae – The greenhouse whitefly is parasitized by this wasp in third and fourth larval instars when Encarsia lay their eggs inside the whitefly scale.
Browse the 2023 Pest Management Guide to learn more.