Garden and houseplant pests

Aphids

• Most established plants tolerate aphid feeding and outgrow the damage; aphids can curl leaves and leave sticky honeydew that draws ants and sooty mold.^[1][10]
• Prune infested leaves and stems, don't over-fertilize (use slow-release products), and protect seedlings with covers or aluminum foil mulch.^[1]
• A strong spray of water from a hose knocks aphids off sturdy plants and washes off honeydew; most dislodged aphids can't get back onto the plant. Spraying early in the day lets plants dry quickly.^[1][10]
• Lady beetles, lacewings, syrphid fly larvae, soldier beetles and tiny parasitic wasps (which leave round, discolored aphid 'mummies') are common natural enemies.^[1][10]
• Natural enemies need time. Minnesota Extension notes that because aphids multiply very fast, predators may take a while to catch up, and UC IPM says that once you see mummies, the aphid population is likely to drop substantially within a week or two.^[10][1]
• Soaps and oils work by smothering aphids, so apply them thoroughly. Soaps and oils only kill the aphids they touch, so spray the undersides of leaves as well as the tops and repeat if needed. Aphids hidden inside curled leaves won't be reached; prune those out.^[1][10]
• Insecticides such as malathion and permethrin may kill more aphids than soaps and oils, but they also kill the natural enemies that give long-term control. Minnesota Extension says longer-lasting products like these can make aphid problems worse.^[1][10]
• Rules on systemic aphid products differ by place. UC IPM, which writes for California, says that as of January 2025 these materials are only available to licensed pest control professionals. Minnesota Extension describes soil-applied imidacloprid and dinotefuran for trees and warns both are very toxic to pollinators, so wait until plants have finished blooming before treating.^[1][10]

Scale insects

• Most plants tolerate low to moderate numbers. Armored scales are tiny and flat with removable covers and no honeydew; soft scales are larger, rounded, and excrete honeydew.^[2][11]
• Look for predators and for parasite emergence holes in scale covers before treating, and control scale-tending ants with sticky barriers or baits.^[2]
• Time sprays to the crawlers, the young mobile stage. To spot them, shake infested branches over white paper or wrap branches with double-sided sticky tape and check it at least once a week; spray after crawler numbers have peaked and begun to decline.^[11][2]
• On fruit trees and smaller plants, a thorough horticultural oil spray during the dormant season or when crawlers are active works. Soaps and oils have minimal impact on natural enemies but only kill crawlers they contact, so scales with a long egg hatch may need repeat sprays.^[2][11]
• A dormant oil spray only works on scales that overwinter as crawlers or adults, not on species that overwinter as eggs. UC IPM says not to spray oystershell or olive scales during the dormant season, because the susceptible stages aren't present then.^[11][2]
• For larger plants, UC IPM suggests considering soil-applied imidacloprid, but says it isn't effective against some scales, including armored scales, and may cause outbreaks of cottony cushion scale. Minnesota Extension agrees it controls most soft scales but not armored scales, and says dinotefuran reduces both. Apply systemics after flowering to protect bees, and always read the label.^[2][11]

Whiteflies

• Inspect new plants before bringing them home. Missouri Extension suggests keeping new plants apart for a few days and checking them before placing them with established plants.^[3][14]
• Hose adults off with a strong stream of water and hang yellow sticky traps, about one per medium-size vegetable plant.^[3]
• Advice on trap numbers varies with plant size: UC IPM's quick guide says one trap for every medium-size vegetable plant, while its longer Pest Note and Missouri Extension say as many as one trap for every two large plants. Missouri suggests putting traps up when whiteflies first appear and taking them down once numbers seem to be dropping, to avoid trapping too many natural enemies.^[3][14]
• A small handheld vacuum can remove adults: vacuum in the early morning, when it's cool and they're slow, then put the vacuum bag in a large plastic bag and freeze it for 24 hours. It helps most when an infestation is just starting.^[14][15]
• Use reflective mulch to protect young plants, and reduce dusty conditions, which disrupt natural enemies.^[3]
• If needed, spray insecticidal soaps or oils, or remove heavily infested plants.^[3][14]
• Even the most toxic insecticides are only partially effective against whiteflies. Whiteflies have developed resistance to some chemicals, and eggs and nonfeeding pupae are less susceptible, so Missouri Extension says eradication usually takes four to five applications at five- to seven-day intervals, aimed at the lower leaf surface.^[3][14]

Spider mites

• Damage is worst in hot, dusty conditions and on water-stressed plants; keep plants watered and dust down. Minnesota Extension suggests checking garden plants every 3-5 days, especially during drought, and says most plants need about one inch of water a week to avoid stress.^[4][12]
• Spray water or mist on the undersides of leaves at least once a day on infested plants.^[4][12][13]
• Forceful hosing also removes the dust that interferes with mite predators.^[13]
• If a pesticide is needed, use an insecticidal oil or soap; broad-spectrum sprays for other pests frequently cause mite outbreaks. Colorado State calls oils at the 2 percent summer rate perhaps the most effective miticide available for home use. Neither soaps nor oils have residual activity, so they only kill mites they hit.^[4][13][12]
• Don't make your own soap solution for mites; Minnesota Extension warns a homemade mix can burn and damage plants.^[12]
• Carbaryl devastates most spider mite natural enemies, and Minnesota Extension says long-lasting bifenthrin and permethrin kill natural enemies and could make infestations worse in the long run.^[13][12]

Mealybugs

• Inspect plants before bringing them home, and discard infested ones. Isolation advice ranges: Wisconsin Extension suggests keeping new houseplants separate for a week or so, Colorado State for at least three weeks.^[5][16][15]
• On houseplants, hand-pick or prune them out, and for serious problems dab them with 70% (or weaker) isopropyl alcohol. Wisconsin Extension suggests a cotton swab or cloth dipped in rubbing alcohol, working best on large-leaved plants; test a small area first, since damage may take a day or two to show.^[5][16]
• On a few small plants, a moderately strong spray of warm water dislodges most mealybugs, though it rarely gets all of them, so check again and repeat.^[16]
• Soaps, horticultural oils and neem oil applied directly to young mealybugs reduce numbers; avoid broad-spectrum insecticides.^[5][16]
• Mealybugs survive on cut plant parts as long as they stay moist, so dispose of prunings right away. Root mealybugs are especially hard to control, and replacing the plant is often the most practical fix.^[16]

Snails and slugs

• Remove daytime hiding places such as boards, stones, weeds and flowerpots, and handpick at night. Water in the morning and at the base of plants, using drip or soaker hoses, so leaves and soil dry before slugs come out at night.^[6][17][18]
• Trap them under a board raised on 1-inch runners and scrape them off daily, or use beer traps buried at ground level. Beer traps attract slugs from only a few feet away, so you'll need several.^[6][18]
• Install a 4- to 6-inch-wide copper band around beds. Minnesota Extension cautions that not all copper tape sold for slugs is wide enough; it must be wide enough that a whole slug can't bridge it.^[6][17]
• Iron phosphate baits are safer around dogs, children and wildlife; metaldehyde baits can poison dogs and birds. Minnesota Extension says iron phosphate keeps working for two weeks even when wet, and Colorado State says it's generally comparable in effectiveness to metaldehyde. Both warn that metaldehyde is hazardous to dogs.^[6][17][18]
• Sources differ on dry barriers. Colorado State says diatomaceous earth, wood ashes and similar materials may give some protection, though moisture reduces the effect; Minnesota Extension says diatomaceous earth is generally not an effective slug deterrent.^[18][17]

Protect the natural enemies

Lady beetles, lacewings, syrphid fly larvae, soldier beetles and tiny parasitic wasps attack aphids and other soft-bodied pests; round, discolored aphid 'mummies' are a sign parasitic wasps are at work.^[1][10]

Broad-spectrum insecticides kill these predators and parasites along with the pests. That's why sprays aimed at other pests frequently cause spider mite outbreaks, and why whitefly outbreaks often follow insecticide use; UC IPM warns that persistent broad-spectrum sprays can cause outbreaks of spider mites or other pests. Dusty conditions also disrupt natural enemies.^[4][3][2][1]

To keep natural enemies around, Minnesota Extension suggests avoiding pesticides or using low-risk products and planting flowers that bloom at different times through the season.^[10]

Cucumber beetles

• Adults are shiny, about 1/4 inch long, with black heads and long, threadlike antennae; they're either greenish yellow with 12 black spots or yellow-orange with three black stripes. Lady beetles look similar but have short, stubby antennae.^[7][20]
• Adults chew leaves, shoots, blossoms and soft fruit, and can spread cucumber mosaic virus and wilts in cucurbits. Nothing will save a plant once it has bacterial wilt; the only way to avoid it is to keep beetles from feeding.^[7][20]
• Most older plants tolerate substantial numbers. Cover emerging plants with protective cloth and remove it once they're big enough to tolerate damage. Take row covers off when plants start flowering, because most cucurbits need insects to pollinate them.^[7][20][19]
• Feeding matters most on small plants. Minnesota Extension says squash and pumpkins can tolerate some feeding once they have four or more leaves, but melons and cucumbers stay vulnerable all season because of bacterial wilt.^[19]
• Remove plants that show bacterial wilt before more beetles feed on them, clear weeds, and clean up garden debris after the season to reduce overwintering sites. A few beetles can be knocked into a bucket of soapy water.^[19]

Tomato hornworms

• Hornworms have a distinctive horn at the rear and grow up to 4 inches long; large black or green droppings under tomato plants usually give them away.^[8][22][23]
• They eat whole leaves and small stems and chew pieces out of green fruit, mostly in midsummer.^[8]
• Larvae hide during the day, so scout in the early morning or evening, and look for dark droppings on leaves and the ground.^[23][22]
• Handpick them or snip them with shears. Natural enemies such as Trichogramma wasps usually keep them in check; Bt or spinosad work on smaller larvae. Utah State suggests dropping them into soapy water.^[8][23]
• If a hornworm is covered with white, rice-like cocoons, leave it: braconid wasp larvae inside are killing it, and the adult wasps that emerge will look for other hornworms.^[22][23]
• Bt only works if the caterpillars eat it.^[22]
• Rototilling after harvest destroys pupae in the soil.^[8][22][23]

Japanese beetles

• Shake beetles off small plants early in the morning, when they're sluggish, into a bucket of soapy water; cover valued plants such as roses with fine netting during peak activity.^[9][21]
• Don't cover plants in bloom that need pollination; Minnesota Extension suggests handpicking until they're done blooming and starting to set fruit, then covering them.^[21]
• Choose plants that are less attractive to the beetles when replacing landscape plants.^[9]
• Skip the traps: University of Kentucky research found they attract many more beetles than they catch, so nearby plants get more damage.^[9][21]
• Controlling grubs in the lawn won't protect landscape plants, because adults fly in from a distance.^[9]
• If you spray, treat foliage thoroughly, avoid windy conditions and times when bees are foraging, and check the label's harvest interval on food crops.^[9]

Using soaps and oils without hurting plants

Insecticidal soaps are usually used as a 1 to 2% solution (2½ to 5 tablespoons per gallon); follow the label and don't mix them stronger. Don't spray in full sun, when it's above 90°F, or on water-stressed plants.^[24][1]

Some plants are sensitive. Spray a small area and wait 24 hours to check for damage before treating the whole plant.^[24][1]

Cover the tops and especially the undersides of leaves. Soap only works while it's wet and has no residual action, so repeat sprays may be needed every 4 to 7 days, following the label.^[24]

Hard water makes soap less effective. To check, mix the soap with your tap water in a glass jar, shake it and let it stand 15 minutes; if scum forms on top, use distilled or bottled water.^[24]

Clemson says homemade soap mixes carry a much higher risk of plant injury, and laundry and dry dish detergents are far too harsh for plants.^[24]

Common questions

Do Japanese beetle traps protect my garden?

No. University of Kentucky research found the traps attract many more beetles than they catch, so nearby plants usually get more damage than with no trap, and Minnesota Extension says not to use them.^[9][21]

Can I make my own insecticidal soap?

It's riskier than buying one. Clemson says homemade mixes carry a substantially higher risk of plant injury, and Minnesota Extension warns a homemade soap solution can burn plants.^[24][12]

Should I kill a hornworm covered in white cocoons?

Leave it. The cocoons belong to a parasitic braconid wasp that kills the hornworm, and the new wasps go on to parasitize other hornworms.^[22][23]

Full guides for each pest

Each pest above has its own guide on this site with identification, life cycle and every treatment option.

• Aphids
• Scale insects
• Whiteflies
• Spider mites
• Mealybugs
• Slugs and snails
• Cucumber beetles
• Tomato hornworms
• Japanese beetles
• Insecticidal soap and horticultural oil

Sources

1. University of California Statewide IPM Program, “Aphids (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/aphids/ (accessed 2026-11-11)
2. University of California Statewide IPM Program, “Scales (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/scales/ (accessed 2026-11-11)
3. University of California Statewide IPM Program, “Whiteflies (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/whiteflies/ (accessed 2026-11-11)
4. University of California Statewide IPM Program, “Spider Mites (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/spider-mites/ (accessed 2026-11-11)
5. University of California Statewide IPM Program, “Mealybugs (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/mealybugs/ (accessed 2026-11-11)
6. University of California Statewide IPM Program, “Snails and Slugs (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/snails-and-slugs/ (accessed 2026-11-11)
7. University of California Statewide IPM Program, “Cucumber Beetles (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/cucumber-beetles/ (accessed 2026-11-11)
8. University of California Statewide IPM Program, “Hornworms (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/hornworms/ (accessed 2026-11-11)
9. University of Kentucky Entomology, “ENTFACT-451: Japanese Beetles in the Urban Landscape (revised March 2026).” entomology.mgcafe.uky.edu/ef451 (accessed 2026-11-11)
10. University of Minnesota Extension, “Aphids in home yards and gardens.” extension.umn.edu/yard-and-garden-insects/aphids (accessed 2026-11-11)
11. University of Minnesota Extension, “Scale insects on Minnesota trees and shrubs.” extension.umn.edu/garden-and-home/yard-and-garden/yard-and-garden-insects/scale-insects (accessed 2026-11-11)
12. University of Minnesota Extension, “Twospotted spider mites in home gardens (J. Hahn, S. Wold-Burkness).” extension.umn.edu/yard-and-garden-insects/spider-mites (accessed 2026-11-11)
13. Colorado State University Extension, “Spider Mites (Fact Sheet 5.507).” extension.colostate.edu/topic-areas/insects/spider-mites-5-507/ (accessed 2026-11-11)
14. University of Missouri Extension, “Whiteflies (G7275, B. A. Barrett).” extension.missouri.edu/sites/default/files/legacy_media/wysiwyg/Extensiondata/Pub/pdf/agguides/pests/g07275.pdf (accessed 2026-11-11)
15. Colorado State University Extension, “Managing Houseplant Pests.” extension.colostate.edu/resource/managing-houseplant-pests/ (accessed 2026-11-11)
16. University of Wisconsin-Madison Extension, Wisconsin Horticulture, “Mealybugs.” hort.extension.wisc.edu/articles/mealybugs-2/ (accessed 2026-11-11)
17. University of Minnesota Extension, “Slugs in home gardens.” extension.umn.edu/yard-and-garden-insects/slugs (accessed 2026-11-11)
18. Colorado State University Extension, “Slugs.” extension.colostate.edu/resource/slugs/ (accessed 2026-11-11)
19. University of Minnesota Extension, “Cucumber beetles.” extension.umn.edu/yard-and-garden-insects/cucumber-beetles (accessed 2026-11-11)
20. University of Kentucky Entomology, “ENTFACT-311: Cucumber Beetles (revised January 2026).” entomology.ca.uky.edu/ef311 (accessed 2026-11-11)
21. University of Minnesota Extension, “Japanese beetles in yards and gardens.” extension.umn.edu/yard-and-garden-insects/japanese-beetles (accessed 2026-11-11)
22. University of Minnesota Extension, “Tomato hornworms in home gardens.” extension.umn.edu/yard-and-garden-insects/tomato-hornworms (accessed 2026-11-11)
23. Utah State University Extension, “Tomato and Tobacco Hornworms.” extension.usu.edu/pests/research/tomato-tobacco-hornworms (accessed 2026-11-11)
24. Clemson Cooperative Extension Home and Garden Information Center, “Insecticidal Soaps for Garden Pest Control (HGIC 2771).” hgic.clemson.edu/factsheet/insecticidal-soaps-for-garden-pest-control/ (accessed 2026-11-11)