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Keep an Eye Out for These 6 Common Garden Pests

Identifying the problem is the first step in finding a healthy way to reduce — or even eliminate — the damage caused by insects. Here are 6 common garden pests you may encounter.

Adapted from Garden Gate magazine with permission


Spotted Cucumber Beetles

Spotted cucumber beetles’ favorite plants: Most any type of flower; also beans, tomatoes, cucumbers, melons and other edibles.

What type of damage do cucumber beetles cause?: Adults chew irregular holes in flowers, leaves and fruit from summer to fall, and larvae (known as Southern corn root-worm) often transmit bacterial wilt disease. In addition to chewing holes, the adult cucumber beetle can carry bacterial wilt and cucumber mosaic virus, both of which quickly kill plants.

How to control spotted cucumber beetles: Mix up and water beneficial nematodes into the soil late in the day in midsummer to control the larvae. To get rid of beetles, grow plants that attract natural predators, such as braconid wasps.


Japanese Beetles

Japanese beetles’ favorite plants: Clematis (Clematis spp. and hybrids), dahlia (Dahlia hybrids), rose (Rosa spp. and hybrids) and Japanese maple (Acer palmatum), to name just a few.

What type of damage do Japanese beetles cause?: Gnawed and ragged flower petals and almost entirely defoliated plants; grubs can be just as destructive, eating the roots of turf in spring and late summer.

How to control Japanese beetles: Pluck or shake beetles off of plants early in the morning and drop into soapy water. Systemic insecticides, such as those containing imidacloprid or thiamethoxam, give long-term protection, and contact insecticides like carbaryl, sold as Sevin®, can be applied as a spray or dust. Late spring to early fall, when grubs are near the soil’s surface, apply a control that contains imidacloprid or halofenozide. Want an organic control? Milky spore, a bacteria you mix with water and sprinkle on the lawn, has killed grubs in some regions.



Scale’s favorite plants: More than 200 species of these sap-sucking insects attack many shrubs and trees (including evergreen, deciduous and fruit).

What damage does scale cause?: Crawlers hatch in late spring and move around briefly before they attach to a leaf or stem to suck sap from tender growth. Leaves turn yellow and drop. Usually damage is minimal for mature trees but can stunt or kill young ones. Scale insects also secrete sticky honeydew.

How to control scale: Lady beetles, parasitic wasps and soldier beetles all feed on scale. For smaller numbers, remove the adults with a cotton swab dipped in soapy water or rubbing alcohol or blast them off with your garden hose. Suffocate adults and eggs by spraying with horticultural oil while the plant is dormant. Cut back and destroy any branches with heavy infestations. 



Grasshoppers’ favorite plants: From vegetables and fruit trees to flowers, grasshoppers aren’t picky eaters.

What type of damage do grasshoppers cause?: Blooms and foliage will look tattered, but a big outbreak can defoliate plants or ruin fruits and vegetables throughout the summer, decreasing your potential harvest later in the season.

How to control grasshoppers: There are pesticides and beneficial pathogens that cause disease in grasshoppers, but they’re hard to use because they have to come in contact with the insect to work, and new grasshoppers are always moving in. Cover important plants or crops with floating row cover or a fine wire mesh. Along with larger beneficial insects, such as the praying mantis, chickens make excellent natural controls.


Tobacco Budworm

Tobacco budworm’s favorite plants: Petunia (Petunia hybrids), flowering tobacco (Nicotiana spp. and hybrids), scented geranium (Pelargonium hybrids) and mum (Chrysanthemum spp. and hybrids), to name a few.

What type of damage do tobacco budworms cause?: Larvae tunnel into or eat entire flower buds, petals and leaf buds; most caterpillars appear in late summer.

How to control tobacco budworms: Handpick caterpillars around dusk, when they’re least active. Buy beneficial insects, such as green lacewing larvae and lady beetles, from sources like gardensalive.com or gardeningzone.com. Release insects on calm days in late spring (either in early morning or evening). Or mix up and spray plants with pyrethroid insecticides until leaves are dripping. These chemicals attack all stages of the insect.



Aphids’ favorite plants: There are thousands of different aphid species, but most pierce and suck sap from a specific kind of herbaceous or woody plant, such as rose (Rosa spp. and hybrids) and juniper (Juniperus chinensis). Other annuals and perennials like zinnia (Zinnia spp. and hybrids) aren’t safe, either.

What type of damage do aphids cause?: Stunted growth and leaf curling, distortion or yellowing; the honeydew (sticky, undigested sap) aphids promote the growth of sooty mold, a black fungus that forms on plants and nearby surfaces, and they also spread viral diseases from plant to plant.

How to control aphids: Knock them off with a strong jet of water or spray the insects thoroughly with insecticidal soap. You can also prune off infected stems and dispose of them in the trash.


How Effective are Organic Pesticides?

Bt (Spray, dust, granules, dunks)

Pests it kills: A specific strain of Bt attacks each type of pest.

  • Caterpillars: Bt kurstaki

  • Beetle larvae: Bt tenebrionis

  • Fly, gnat and mosquito larvae: Bt israelensis

How it works: Bt is a naturally occurring soil-born bacteria that destroys the targeted insect’s digestive system when it’s ingested, usually in the larval stage.

Tips for success: Breaks down in sunlight, so you may need to reapply every three to five days. Bt dunks can be dropped in water features to control mosquitoes. Scratch granules into houseplant soil and water to kill fungus gnat larvae.


Horticultural Oil (Ready-to-use spray or concentrate)

Pests it kills: Works best on insect eggs, juvenile stages and soft-bodied insects; most often used for: Aphids, Mites, Scale

How it works: Made of highly refined petroleum oils that coat and suffocate insects. Some oils may poison the insect by disrupting their feeding or metabolism as well.

Tips for success: Product needs to coat the insect thoroughly. Apply lightweight summer oil in the growing season to treat problems and heavy dormant oil in winter before insects do damage. Once dried, horticultural oil will not harm beneficial insects.


Horticultural Soap (Ready-to-use spray or concentrate)

Pests it kills: Kills all insects; most often used for: Aphids, Boxelder bug nymphs, Japanese beetles, Mealybugs

How it works: Specially formulated soap with fatty acids washes away the insect’s waxy protective outer coating so it dehydrates and ultimately dies.

Tips for success: Product needs to coat the insect thoroughly to be effective. Be sure to spray the undersides of leaves to reach insects hiding there.


Neem (Ready-to-use spray, dust, wettable powder)

Pests it kills: Kills all insects; most often used for: Aphids, Beetles, Mites, Scale, Whiteflies, Powdery mildew, Leaf spot

How it works: Oil from the seeds of the neem tree (Azadirachta indica) interferes with insects’ feeding, growth and reproductive hormones when eaten.

Tips for success: Neem also smothers fungus spores, making it a good fungicide to stop powdery mildew and leaf spot.


Pyrethrum (Ready-to-use spray, dust)

Pests it kills: Kills all insects; most often used for: Aphids, Beetles, Caterpillars, Wasps, Whiteflies

How it works: Pyrethrum is made from the seeds of Dalmation chrysanthemum (Chrysanthemum cinerariaefolium) and affects the transmission of impulses to and from the brain when eaten by insects. 

Tips for success: Breaks down quickly in sunlight, so it needs to be applied about every week. Pyrethrum works quickly, so it is used in many wasp sprays. It also works as a repellent for some insects.


Spinosad (Ready-to-use spray, dust, granules)

Pests it kills: Kills all insects; most often used for: Caterpillars, Flies, Leafminers, Thrips

How it works: Contains the soil-born bacterium Saccharopolyspora spinosa. When it’s eaten or absorbed, it disrupts the insect’s nervous system.

Tips for success: Apply it early in the morning or late at night so it dries before bees become active. Spinosad breaks down quickly in sunlight and may need to be reapplied as often as every few days, but it depends on the situation, so follow label directions.


See Also: How to Start a Truly Organic Garden

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