Bag WormsBagworms

Bagworms are caterpillars that form a small bag or cocoon - like pouch that hangs down on the leaves and branches of shrubs and trees. The bags are made of silk, with bits of twigs and leaves interwoven to disguise and strengthen the bag. The larvae or caterpillar eats the foliage of the plant. Their feeding can cause extensive damage to several different ornamental trees and shrubs.


Twenty species in the United States.


128 plants. Mostly Arborvitae, Juniper, Cedar, Elm, White Pine, Honeylocust, Norway Maple, Hemlock Spruce


If your shrubs have a small infestation, pick the bags off the plant. Put them inside a jar or coffee can and dispose of them in the garbage can. Bags left hanging on the shrub or tree contain females that can produce 500 to 1000 eggs within the bag. They will overwinter, and hatch the following May.
For larger infestations, spray the entire shrub. It will take 2 to 3 sprayings, with a one-week interval between each. For best results, treatment must be made when the bags are still small. Watch for bagworms in late May and early June and treat at the first signs of activity.
Spray with one of the following:. Pesticides vary in strength.


  • Garden Tech Sevin = Concentrate, Hose-end-Sprayer and Ready-to-Use trigger spray
  • Ortho Systemic Insect Killer = C, HES, RTU
  • Bonide Malathion Insect Control = C only
  • Bayer Advance Garden Power Force Multi-Insect Killer = C only
  • Bonide Eight Insect Control = C, HES, RTU
  • *Bonide Thuricide = ("BT"; i.e., Bacillus Thuringiensis) = C only
  • *Montery Garden Insect Spray = C only
  • *Safer Bio-Neem Insecticide & Repellant = C, HES, RTU
  • *Organocide = C, HSE, RTU

(* denotes Organic Product)


Borers are generally the larvae form of various beetles or moths that feed inside stems, trunks, branches or twigs. A few adult beetles will bore into plants. Borers are most destructive in trees and shrubs, but will feed on annuals, perennials and vegetables as well. Some common borers in this area attack Dogwood, Cherry, Lilac, Pine and Rhododendron. Borers are among the most destructive and difficult to control insect pests in the landscape.

The borer life cycle begins when eggs are laid in the cracks and crevices of bark, preferably in open wounds and protected locations, i.e. under tree wraps or mulch. Once the eggs hatch, the larvae begins to chew its way into the plant. This is when the damage occurs.

When borers feed, they destroy the tissues in the plant needed to conduct water and nutrients. The result is slow, stunted growth, branch dieback or death of the entire plant. Sap or sawdust may be visible at the entry or exit holes of the borer. When the borer reaches maturity, the adult moth or beetle will chew an exit hole, emerge from the plant and begin looking for a mate. This process, from egg to adult can take several weeks or several years, depending on the type of borer.



Non-Chemical Controls

Borers will infest weak, stressed plants. To reduce borer infestation, maintain plant health through watering, fertilizing and pest control.

  • Remove any mulch piled up against the base of trees and shrubs
  • Avoid wounding the bark and closely monitor any existing wounds for signs of borer activity
  • Remove and destroy heavily infested plants
  • Inject Parasitic nematodes into borer galleries as a biological control
  • Use floating row covers to prevent borers in vegetable crops

Chemical Controls

Spray the stem, trunk, branches or twigs of the susceptible plant during the egg-laying season of the borer. Timing is critical to successfully controlling borers. Once the borer has gained entry into the plant, pesticide applications are ineffective. The accompanying chart lists the treatment dates for several of the most common borers.

Recommended Pesticides

  • Borer-Miner Killer - applied every 4 weeks
  • Advanced Garden Tree & Shrub Insect Control - applied once per growing season. Flathead, Roundhead and Bronze Birch Borers only. Not for edibles

Please bring plant or insect samples to Merrifield Garden Centers' Plant Clinic for assistance identifying borers and selecting pest control products. ALWAYS READ AND FOLLOW LABEL DIRECTIONS WHEN USING PESTICIDES.

Pesticide applications need to be repeated throughout the treatment times at regular intervals as directed on the product label.


Deer ResistentDeer Resistant Plants

The destruction of landscape plants by deer has become widespread throughout the Washington D.C. area. As development destroys habitat and eliminates predators, deer have adapted to suburban life and their population has grown, increasing demand and competition for food. Landscape plants have become a primary source of food for deer, and deer have become a source of aggravation for gardeners. In late winter and early spring this becomes especially troublesome as sources of food are very limited.

There are several tactics available to deter deer. No single approach is completely effective. Experiment and combine these tactics to determine what is most effective in your garden.




A physical barrier is the most effective method to keep deer from foraging. A 7' tall fence is required to be effective. Deer fencing should be within easy view of the deer and should lean out towards the deer, away from your garden. A fine mesh is used for the black plastic fencing, which does not detract from the beauty of your landscape. If fencing is not practical, drape deer netting over vulnerable plants. Anchor or fasten deer netting to the ground to prevent the deer from pulling it off of the plants.


Deer repellents work either through taste, scent, or a combination of both. Repellents that leave a foul taste to the plant are more effective and last longer than scent repellents. There are many different repellents and results vary depending on feeding pressures. Begin using repellents early and alternate between different brands. As deer grow accustomed to a particular repellent, the repellant becomes less effective and it gets harder to deter the deer. The time between applications varies with weather. The following time frames are based on the experience of our customers and staff. Results will vary. Always read and follow label directions.


Deer have clear preferences in the plants they choose to feed on. Using plants that have prickly or fuzzy foliage or a strong aroma will discourage their feeding. Almost any plant is susceptible to deer damage, and when food is limited deer may feed on less favorable plants. Localized differences in deer taste do exist. The following is a generalized list compiled from many sources. For further information about controlling deer, please speak with a member of our professional staff.

  • Perennials
  • Vines
  • Trees
  • Shrubs
  • Herbs
  • Annuals & Tropicals
  • Bulbs

Gypsy Moths & Tent Caterpillars

Gypsy moths & tent caterpillars can do serious damage to ornamental & shade trees in our area. They are active in the early spring and similar in appearance. They are often confused with each other, but the controls are the same for both.


Gypsy moth larvae feed on the foliage of host plants in April to May for seven to eight weeks. They hide in shady places during the day and begin to feed at night. On heavily infested trees, they may feed during the day. Gypsy moth larvae are very hairy, with two rows of blue dots on the first third of their bodies and red dots on the last two thirds. They can grow up to 2 inches.
Most trees can withstand one or two consecutive years of defoliation before severe decline or death. Needle evergreens may die after one complete defoliation because they are unable to replenish all their needles.


Apple, Alder, Basswood, Hawthorn, Hemlock, Oak, Pine, River Birch, Spruce, Willow

Less Common Hosts

Black Birch, Paper Birch, Yellow Birch, Black Gum, Cherry, Cottonwood, Elm, Hickory, Hornbeam, Larch, Maple, Sassafras.

Chemical Control: Sevin, Eight, or Methoxychlor Non-Chemical: Thuricide, or Dipel are Bacillus Thuringiensis products. Montereys' Garden Insect Spray

Applications should be done in the early evening, as insects are active at night. Wrapping trees in burlap or sticky foil will help prevent insects from climbing to the tops of trees. Burlap must be removed during the day so that larva can be collected and killed. The control for adult moths is a trap for males that can prevent mating and subsequent generations.


The eastern tent caterpillar is the most prominent in this area. Larvae are black, with white stripes down their backs and yellow lines with blue dots down their sides. They hatch out and reach maturity at 2" in about six weeks. The caterpillars spin silky webs in the forks of trees in April to May. They enlarge the tent as they grow, sometimes covering entire branches.


Apple, Birch, Black Gum, Cherry, Crabapple, Hawthorn, Peach, Plum, Wild Cherry

Chemical Control: Sevin, Eight, or Methoxychlor Non-Chemical: Thuricide, Dipel. Montereys Garden Insect Spray

Early morning applications are the most effective as tent caterpillars feed during the day and return to the tent at night. Break open the tent if possible prior to spraying. You can also remove and destroy the tents at night. Control is only effective while caterpillars are still growing. Once mature, they stop eating and spin a cocoon.


Japanese BeetleJapanese Beetle

Japanese Beetles create havoc in area gardens by feeding on ornamental trees, shrubs, perennials and lawns. They begin life as a grub feeding on plant roots, maturing into adult beetles that feed on flowers and foliage. Japanese beetles are especially troublesome insect pests not only because they feed above ground and below ground, but also because they can occur in huge numbers capable of destroying lawns and gardens in a very short period of time. Fortunately, there are several different strategies to control this pest. A review of the history and life cycle of the Japanese Beetle may help you to decide on the best method of controlling this pest in your garden.


The Japanese Beetle was accidentally imported into this country in 1916 and has spread throughout the northeast and mid-Atlantic regions. Adult beetles emerge from the ground in late June or early July and live for 30-45 days. During this time, they feed on many favorite landscape plants including Crape Myrtle, Flowering Cherry, Grape, Hibiscus, Contorted Filbert, Linden, Roses and many others. Japanese Beetles have been reported feeding on almost 300 different plant species.
In late July to early August, the female will burrow into the soil, lay eggs and die. The eggs hatch within two weeks and the emerging grubs (larvae) begin feeding on plant roots. The grubs often concentrate in lawns where the dense, fibrous roots provide ample food. The grubs continue feeding and growing until cold temperatures drive them deep into the ground where they wait out the winter months. As spring approaches, the grubs resume feeding until reaching maturity in late spring.


To kill these beetles, use ONE of the following insecticides: (Please refer to the lawn care bulletins for information on grub control)
MALATHION, MERIT, METHOXYCHLOR, SEVIN, or TEMPO; repeat applications as necessary.



Traps can be used to reduce the number of Japanese Beetles, but will not provide total control of this pest. Traps should be placed 25' or more downwind from the plants you are trying to protect and placed 4'-5' above the ground.

Follow the direction on the trap you purchase as they vary with each type of trap.


Lace BugsLacebugs

Lacebugs are small insects (about 1/8 inch) that damage several ornamentals by sucking fluids out of the leaves. The damage shows up as a discoloration of the leaves, leaving them almost silver. It is similar in appearance to mite damage, except that the clorotic spots are larger. The most evident sign of present insects is a brownish-black, tar-like residue underneath the leaves. Feeding insects excrete this material. Usually the insects are rarely seen because they are small and appear on the undersides of the leaves.
Adults have lace-like, clear wings, but may be brown, tan, or white as there are over 27 different species in the U.S. Immature lacebugs are dark, wingless insects with spines radiating from the edges of their bodies. They move in a sideways manner, but are rarely seen. Eggs are inserted into the leaves along the midribs, on the undersides. Cone-like caps cover the eggs, projecting out from the bottoms of the leaves.

Several generations are present each year, the first generation usually in May, with most lacebugs over-wintering in egg form. (However, some lacebugs over-winter as adults, under bark of trees and shrubs.)


There are over 50 known hosts, but in our area the most common are Andromeda, Azalea, Beech, Birch, Chrysanthemum, Cotoneaster, Hawthorn, Linden, Oak, Pyracantha, Rhododendron, and Sycamore.


Lacebugs can be controlled with a variety of contact or systemic insecticides. Contact insecticides must be applied to the undersides of the leaves where the lacebug will come into contact with the insecticide. For this reason, systemic insecticides which are absorbed through the foliage and subsequently ingested by the lacebug, are often more practical for control of this pest. Insecticides should be applied anytime from May-September where lacebugs are active.


Ortho Systemic Insect Killer, Bayer Advanced Rose & Flower Insect Killer
Bayer Advanced Tree and Shrub Insect Control


Sevin, Pyrethrin, Insecticidal Soap, Horticultural Oil, Permethrin, Resmetherin

Slugs and SnailsSlugs and Snails

Slugs and snails feed on a variety of plants leaving ragged, irregular shaped holes in the leaves or devouring entire seedlings. Plants with soft, succulent leaves, like hosta, lettuce, peppers, marigolds, and dahlias, are their favorites. If there are ragged holes in your annuals, perennials, or vegetables, but you see no insects, slugs and snails have likely been dining in your garden. Slugs devour foliage, while snails eat decaying organic matter. In the Washington area, slugs are generally a greater problem than snails.
Slugs and snails emerge from winter resting-places to begin feeding in the spring. They lay egg masses repeatedly through the warm months. The eggs hatch in four weeks and mature in several months. Slugs and snails need cool, moist conditions to survive. They typically spend the daylight hours hiding under leaves, rocks, and sticks, waiting for cool wet evenings when they come out and feed. Slugs and snails may feed during the daytime on cool, overcast days.


Many methods of controlling slugs and snails have been tried with varying degrees of success. Early intervention, in April or May, will help reduce the population for the months to come. The first step is to remove excess leaf litter, boards or other hiding places.


Place cabbage leaves, grapefruit rinds, or boards in the garden to provide a place for slugs and snails to hide. Check these traps each morning and destroy the slugs. Concern makes an excellent trap called "The Pit" which works quite well.


Put copper tape around flowerpots or specimen plants. Slugs and snails will not crawl over the copper. Sprinkle Concern diatomaceous earth, wood ash or crushed eggshells on the surface of soil or mulch. These materials are abrasive and irritating. They must be reapplied after rainfall. Concern also makes a product called Slug Stop which works as a barrier.


Rosemary plants deter slugs and snails. Decollate snails are natural predators for garden snails. Merrifield carries decollate snails seasonally or can order them for you.


Pelletized, granular and liquid baits are available to attract and kill slugs and snails. They are convenient and effective. They need to be reapplied every two weeks. Do not use these products around children, dogs, cats, or other wildlife that may be attracted to the bait and accidentally poisoned. Apply to the soil, not the plants. Always read and follow label directions when using pesticides. Products include Bug-Geta, Bug Geta Plus, Deadline, and Sluggo.

Spider MitesSpider Mites

Description: Small, pepper sized, red, green, brown or yellow spider; barely visible to the eye. They have eight legs. Female lay six eggs per day, 72 eggs per lifetime, and can produce a dozen generations per year. Most favorable conditions for mite development is hot, dry weather.
Symptoms: Tiny cobwebs over leaves or needles, although not in all cases. Leaves and needles turn pale yellow and then brown. Leaves are mottled or spotted. The needle evergreens show a dull color and brown out.

Control: On trees, shrubs, evergreens and vegetables, use any one of the following pesticides:

  • Malathion
  • Cygon
  • Kelthane

Control: For around buildings, foundations, patios, picnic areas and lawns: Malathion

Spraying for mites is done when needed. Generally the problem occurs in June, and again in September. It may take from 2 to 3 sprayings at 7-10 day intervals to control spider mites. Cover the entire plant.