From beetles to worms and everything in between, garden pests are out in full force during the summer months in Michigan. Whether you're growing vegetables, annuals, perennials, or houseplants, chances are you've encountered at least one of these unwelcome visitors. Below, we’ve rounded up 10 of the most common pests we see this time of year—along with what to look for, symptoms to watch, and the most effective treatment options using products we carry right here at Deneweth’s.
⚠️ Product Use Reminder:
Always read and follow label directions for safe, effective application.
Scroll to learn more about Aphids, Spider Mites, Tomato Hornworms, Japanese Beetles, Slugs, Sawfly Larvae, Thrips, Mealybugs, Whiteflies, Cabbage Worms.
Aphids
Aphids are tiny, sap-sucking insects that multiply quickly and cluster on new growth. They’re especially common in mid to late summer and can cause serious damage if left untreated.
What to Look For:
Tiny green, black, brown, or white insects clustering on the undersides of leaves, along stems, or around flower buds. They often appear in large groups and can be found on vegetables, roses, annuals, and perennials.
Symptoms
- Sticky residue on leaves (called honeydew)
- Yellowing, curling, or distorted new growth
- Ants crawling on the plant (they’re attracted to the honeydew)
Solutions
- Rinse with water: Spray plants with a strong blast of water to knock aphids off. This can reduce light infestations, especially when repeated every couple of days.
- Use Insecticidal soap or neem oil: Both products are safe and effective on soft-bodied pests like aphids. Apply thoroughly to stems and the undersides of leaves. Repeat every 5–7 days as needed.
- Try a Soapy Water Spray: Mix a few drops of dish soap into water and spray affected areas. Reapply every 2–3 days for up to 2 weeks. (Avoid using in direct sun or high heat.)
- Treat Heavier Infestations with Contact or Systemic Control: For larger outbreaks or persistent problems, try products that kill on contact or systemically protect the plant from within.
Recommended Products
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Bonide Insecticidal Soap
Fast-acting contact spray that knocks down aphids quickly. Safe for use on vegetables, herbs, houseplants, and flowering plants. -
Bonide Neem Oil
Organic option that smothers aphids and helps prevent future outbreaks. -
Bonide Eight Insect Control
Powerful contact insecticide that provides strong knockdown of aphids. Best for outdoor ornamentals and woody plants. Not recommended for use on edibles—check label for details. -
Bonide Systemic Insect Spray
Absorbs into the plant for long-lasting internal protection. Ideal for shrubs, roses, and other landscape ornamentals. -
Sevin Insect Killer
Effective contact control for heavy infestations on non-edible plants. -
Ferti-lome Triple Action (VPG)
A 3-in-1 solution that targets aphids, mites, and fungus all at once.
Spider Mites
Spider mites thrive in hot, dry weather and dusty conditions, making late summer a prime time for outbreaks in Michigan gardens.
What to Look For:
Extremely tiny red, yellow, or greenish mites, often too small to see without a magnifying glass. Check the undersides of leaves for activity.
Symptoms
- Fine webbing between leaves or on undersides
- Leaves look dusty, speckled, or bronze
- Leaves may curl, drop early, or appear scorched or faded
Solutions
- Rinse Regularly: Spray plants with a strong stream of water—especially the undersides of leaves—to dislodge mites. Repeat every few days, as spider mites multiply quickly.
- Increase Humidity: Spider mites thrive in dry conditions.
- Apply Insecticidal Soap or Horticultural Oil: Thoroughly coat both sides of the leaves—these products must contact the mites to be effective. Repeat every 5–7 days for 2–3 cycles to break the life cycle.
- Use a Targeted Miticide: Some insecticides won’t work on mites. For heavy infestations, use a product specifically labeled for spider mite control.
Recommended Products
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Bonide Mite-X
All-natural botanical miticide that kills mites on contact. Best used early in the infestation. -
Bonide All Seasons Horticultural Spray Oil
Smothers mites and their eggs. Great for both active outbreaks and dormant season protection.
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Bonide Neem Oil
A triple-action organic option that targets eggs, larvae, and adult mites while also managing fungal issues.
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Bonide Insecticidal Soap
A gentle, fast-acting contact spray. Safe for vegetables, herbs, and flowers. -
Ferti-lome Triple Action (VPG)
A powerhouse 3-in-1 that controls mites, insects, and fungal diseases. Great for ornamental and edible plants.
Tomato Hornworms
Tomato hornworms are large, green caterpillars that can quickly defoliate your tomato plants—and they’re most active in mid to late summer. They also feed on peppers, eggplant, and potatoes, but tomatoes are their favorite target.
What to Look For:
Big green caterpillars (up to 4 inches long) with white diagonal stripes and a curved horn on their rear end. They blend in with tomato leaves, so look closely!
Symptoms of Tomato Hornworms
- Large, chewed holes in leaves and stems
- Missing sections of tomatoes (especially green fruit)
- Frass (droppings)—dark green or black pellets on leaves or around the base of the plant
- Significant defoliation at the top of the plant
- Wilting or slowed growth in severe cases
Solutions
- Handpick Daily: The most effective and immediate method. Look early in the morning or late in the day. Drop hornworms into a container of soapy water to dispose of them.
- Apply Bt (Bacillus thuringiensis): An organic treatment that targets caterpillars. Hornworms ingest Bt as they feed, which stops them from eating and kills them within days.
- Use a Targeted Spray: For quicker results or heavier infestations, use contact insecticides that are safe for use on edible plants.
Recommended Products
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Bonide Bt (Thuricide)
Organic biological control that targets caterpillars only—safe for pollinators and people. -
Bonide Captain Jack’s Deadbug Brew
Contains Spinosad for effective control of hornworms and other chewing insects. Safe for use on edibles. -
Bonide Tomato & Vegetable Insect Control Concentrate
Fast-acting insecticide formulated specifically for use on vegetables like tomatoes, peppers, and eggplant. - Ferti-lome Triple Action (VPG) A 3-in-1 product that works against insects, mites, and fungal issues. Safe for use on tomatoes and other vegetables.
Japanese Beetles
Japanese beetles are one of the most recognizable—and destructive—garden pests in Michigan during mid to late summer. These metallic green beetles chew through leaves, flowers, and fruit, often feeding in large groups.
What to Look For:
Shiny green and copper beetles, often seen feeding in clusters on roses, hibiscus, grapes, fruit trees, beans, and other ornamentals.
Symptoms
- Skeletonized leaves—only the veins remain
- Flowers chewed from the edges inward
- Clusters of beetles feeding on the same plant
- Rapid defoliation and plant stress
Solutions
- Handpick in the Morning: Beetles are sluggish early in the day. Drop them into a bucket of soapy water to reduce population quickly.
- Avoid Beetle Traps Near Gardens: Traps attract beetles from a wide area and can worsen infestations if placed too close to your plants.
- Use Contact Insecticides: Apply sprays directly to beetles and foliage. Reapply after rain or every few days during heavy feeding periods.
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Use Systemic Protection on Ornamentals:
For long-lasting control, use systemic products that protect plants from the inside out (not recommended for edible plants).
Recommend Products
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Bonide Japanese Beetle Killer
Ready-to-use contact spray that kills beetles on contact. Ideal for roses and ornamentals. -
Bonide Eight Insect Control
Broad-spectrum spray that kills on contact and provides residual protection. Best for ornamentals. -
Bonide Systemic Insect Spray
Absorbs into plant tissue for long-lasting protection. Ideal for trees, shrubs, and flowers—not for use on edibles.
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BioAdvanced 12 Month Tree & Shrub Protect & Feed
Provides year-long systemic protection from Japanese beetles and other pests. Great for large landscape plants.
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Sevin Insect Killer
Fast knockdown of beetles on contact. Effective on ornamentals; use with caution and avoid spraying during pollinator activity.
Slugs
Slugs may be slow, but the damage they cause happens fast—especially during cool, damp weather or after watering. They're especially active at night and love feeding on tender leaves, flowers, and seedlings.
What to Look For:
Soft-bodied, gray or brown mollusks hiding under mulch, pots, or dense foliage. They’re usually spotted in early morning, evening, or after rain.
Symptoms
- Irregular, ragged holes in leaves, especially on hostas, lettuce, marigolds, and young seedlings
- Silvery slime trails on soil, pots, or plant surfaces
- Damage concentrated in shady, moist areas of the garden
- In severe cases, plants may be chewed down to stems overnight
Solutions
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Handpick in the Evening or Early Morning: Check plants at dawn or dusk and remove slugs manually. Drop them into soapy water to dispose of them.
- Eliminate Hiding Spots: Remove excess mulch, wood boards, or dense ground cover where slugs can hide during the day. Lay pieces of cardboard on the bare soil around your plantings. Leave the cardboard overnight and check underneath it in the morning and dispose of the slugs found there.
- Apply Iron Phosphate Baits: Iron phosphate-based slug baits are effective and safe for use around pets, people, and wildlife. Reapply as needed, especially after rain or heavy watering.
Recommend Products
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Sluggo
Pet-safe, organic slug and snail bait that uses iron phosphate to eliminate pests. Can be used around vegetables, flowers, and ornamentals. Rain-resistant and OMRI listed for organic gardening.
Sawfly Larvae
Sawfly larvae look like small caterpillars, but they’re actually related to wasps—and they can quickly skeletonize leaves on roses, hibiscus, dogwoods, and more. These pests are active from spring through late summer, depending on the species.
What to Look For:
Green or yellowish worm-like larvae (often with black spots or heads), usually seen feeding in groups on leaf surfaces. Unlike true caterpillars, sawfly larvae have more than 5 pairs of prolegs.
Symptoms
- Holes or skeletonized leaves, often starting at the edges
- Leaf surfaces stripped clean, leaving just the veins
- Groups of larvae feeding together, especially on young, tender foliage
- Damaged areas may turn brown and drop prematurely
Solutions
- Handpick When Possible: If the infestation is small, remove larvae by hand and dispose of them in soapy water.
- Apply Bt? Nope! Bt (Bacillus thuringiensis) only works on true caterpillars, not sawflies. You’ll need products specifically labeled for chewing insects.
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Use Contact or Systemic Insecticides: Apply sprays when larvae are actively feeding. Focus on coating leaves thoroughly—especially the undersides.
Recommend Products
- Bonide Eight Insect Control - A highly effective contact insecticide for sawfly larvae on roses, hibiscus, dogwoods, and other ornamentals. Provides residual protection. Best for outdoor use on non-edible plants. Kills on contact—great for fast control.
- Bonide Systemic Insect Spray - Absorbs into the plant to offer long-lasting protection against chewing pests like sawfly larvae. Ideal for trees, shrubs, and landscape ornamentals. Not for use on edibles.
- Sevin Insect Killer - Strong knockdown insecticide for contact control of sawfly larvae. Use on ornamentals only—check label for application guidelines. Avoid use during pollinator activity
- BioAdvanced 12 Month Tree & Shrub Protect & Feed - Provides extended systemic protection against sawflies and other pests. Great for larger trees and shrubs where spraying is difficult. Not for edible plants. Also offers feeding benefits to strengthen plants.
- Bonide Captain Jack’s Deadbug Brew - Contains Spinosad—may offer some control on young larvae, though it's not highly effective for sawflies. Best used when treating mixed pest problems like caterpillars or thrips alongside sawfly larvae.
Thrips
Thrips are tiny, slender insects that feed by puncturing plant cells and sucking out the contents. This causes distortion, discoloration, and scarring on flowers and leaves. They thrive in warm, dry conditions and can be tough to spot without close inspection.
What to Look For:
Tiny, fast-moving insects—often yellow, brown, or black—usually found inside flowers, on buds, or between tightly curled leaves.
Sypmtoms
- Silvery or bronze streaks on leaves or petals
- Distorted, curled, or stunted new growth
- Deformed flowers or buds that fail to open
- Tiny black specks (thrips droppings) on leaves
- General decline or loss of vigor in affected plants
Solutions
- Rinse or Prune Heavily Affected Areas: Use a strong stream of water to knock off thrips and remove badly damaged plant parts to reduce population.
- Apply Contact Sprays Thoroughly: Thrips are tiny and fast, so thorough coverage—especially of buds and leaf undersides—is key. Repeat applications may be needed.
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Use Systemic Insecticides on Ornamentals: For ongoing control in trees, shrubs, or flowers, systemic products can offer long-lasting protection.
Recommended Products
- Bonide Insecticidal Soap - A great first step for thrips on houseplants, herbs, vegetables, and flowers. Kills on contact by disrupting soft-bodied insects. Safe for edibles and indoor use. Must be applied directly to insects—repeat every few days.
- Bonide Captain Jack’s Deadbug Brew - Contains Spinosad—excellent for controlling thrips, especially on vegetables and flowers.
- Bonide Neem Oil - Organic, multipurpose treatment that helps control thrips at all life stages—eggs, larvae, and adults. Best for early infestations and repeat use.
- Ferti-lome Triple Action (VPG) - A 3-in-1 insecticide, miticide, and fungicide. Very effective for ornamentals and edibles alike when dealing with complex pest issues.
- Bonide Systemic Insect Spray - Long-lasting internal protection for non-edible ornamentals like roses and shrubs.
- Sevin Insect Killer - Fast knockdown of thrips on contact. Best for ornamental use—avoid spraying during pollinator activity.
Mealybugs
Mealybugs are soft-bodied insects covered in a white, cotton-like coating. They cluster in leaf joints, stem nodes, and roots, feeding on plant sap and weakening your plants over time. They’re especially common on houseplants, succulents, and greenhouse plants—but can also show up on garden ornamentals in warm, humid conditions.
What to Look For:
White, fuzzy clusters in crevices where leaves meet stems, or on roots if you unpot the plant. They may look like bits of cotton or fluff.
Symptoms
- Sticky residue (honeydew) on leaves or nearby surfaces
- Yellowing, curling, or stunted growth
- Black sooty mold developing on honeydew
- Leaves dropping or general plant decline
- On houseplants: white fuzz on soil, stems, or leaf undersides
Solutions
- Isolate Infected Plants (Indoors): Prevent spreading by moving affected plants away from others, especially in indoor settings.
- Remove with Rubbing Alcohol: Dab mealybugs with a cotton swab dipped in 70% isopropyl alcohol. This dissolves their protective coating and kills them on contact.
- Apply Insecticidal Soap or Neem Oil: Spray thoroughly, making sure to coat hidden areas like leaf axils and stem joints. Repeat every 5–7 days until the infestation is gone.
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Use a Systemic Insecticide (For Ornamentals): Systemic products protect from within the plant and are effective against hidden infestations, especially for outdoor shrubs and trees.
Recommended Products
- Bonide Insecticidal Soap - A safe and effective contact spray for soft-bodied pests like mealybugs. Works well on houseplants, succulents, herbs, and ornamentals. Must come into direct contact with the pest.
- Bonide Neem Oil - A natural, organic option that smothers mealybugs and helps manage the black sooty mold that grows on honeydew. Safe for edibles and indoor plants. Also treats fungal issues.
- Bonide Systemic Insect Spray - Long-lasting protection for ornamental plants—great for preventing reinfestation.
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Ferti-lome Triple Action (VPG) - A 3-in-1 product that tackles insects, mites, and fungal diseases—especially useful for outdoor container plants, or where multiple problems occur.
Whiteflies
Whiteflies are small, moth-like insects that fly up in clouds when plants are disturbed. They cluster on the undersides of leaves and suck plant sap, weakening your plants and leaving behind sticky residue that encourages disease. They're especially common in vegetable gardens and on houseplants during the warm summer months.
What to Look For:
Tiny white insects (about 1⁄16") fluttering around plants when touched. Adults and their tiny oval eggs or larvae are usually found on the undersides of leaves.
Sypmtoms
- Leaves turning yellow, wilting, or dropping prematurely
- Sticky honeydew on foliage, often followed by black sooty mold
- Reduced plant vigor and slow growth
- Clouds of tiny white bugs flying off when plants are disturbed
Solutions
- Rinse with Water: A strong spray can dislodge adults and larvae. Focus on leaf undersides and repeat regularly.
- Use Sticky Traps (for Monitoring): Yellow sticky traps help monitor whitefly populations and reduce adults indoors.
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Use Systemic Insecticides on Ornamentals: For ongoing control in trees, shrubs, or flowers, systemic products can offer long-lasting protection.
Recommended Products
- Bonide Insecticidal Soap - Excellent for knocking down whiteflies on contact. Safe for use on vegetables, herbs, flowering plants, and houseplants. Must be sprayed directly on the insects—focus on leaf undersides.
- Bonide Neem Oil - Organic option that works on whitefly adults, eggs, and larvae. Also helps reduce black sooty mold that forms on honeydew. Safe for use indoors and on edibles
- Bonide Systemic Insect Spray - For non-edible ornamentals, this product absorbs into plant tissue to protect from within. Helpful for tough or repeated infestations.
- Ferti-lome Triple Action (VPG) - A highly effective 3-in-1 product that acts as an insecticide, miticide, and fungicide. Great for whiteflies and related fungal issues. Works on vegetables, flowers, shrubs, and ornamentals
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Sevin Insect Killer - Powerful contact control for large outbreaks. Use on ornamentals; avoid spraying when pollinators are active.
- Bonide Captain Jack’s Deadbug Brew - Contains Spinosad, which is effective on whiteflies, especially in container gardens, and ornamentals. Safe for use on edibles. Offers strong control with minimal impact on pollinators when applied responsibly.
Cabbage Worm
These green caterpillars are common in vegetable gardens, especially on members of the cabbage family—broccoli, kale, cauliflower, Brussels sprouts, and more. They feed heavily on leaves, making ragged holes and leaving behind droppings. Active from spring through fall, they’re a major problem in Michigan gardens during late summer and fall harvests.
What to Look For:
Light green caterpillars (often inching like a “looper”), hiding on leaf undersides and along leaf veins. You may also notice small, white moths fluttering nearby—these are the adult stage of the pest.
Sypmtoms
- Irregular holes in leaves, especially on younger plants
- Frass (dark droppings) on leaves or around the base of the plant
- Leaves chewed down to veins or stems
- Reduced harvest size and plant vigor
Solutions
- Handpick Caterpillars: Inspect plants regularly, especially the undersides of leaves. Remove caterpillars and drop into soapy water.
- Apply Bt (Bacillus thuringiensis): This natural bacteria targets caterpillars only—safe for bees, pets, and people. Works best when caterpillars are young and actively feeding.
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Use Organic or Contact Insecticides: Apply thoroughly and repeat as needed. Always coat both sides of the leaves, especially in cool, shaded areas where caterpillars hide.
Recommended Products
- Bonide Bt (Thuricide) - A top-choice organic solution for cabbage worms and loopers. Contains Bacillus thuringiensis (Bt), which kills caterpillars after ingestion without harming people, pets, or beneficial insects. Safe for edible crops like cabbage, kale, broccoli, and cauliflower
- Bonide Captain Jack’s Deadbug Brew - Contains Spinosad, which is very effective for controlling cabbage worms and other chewing insects. Quick knockdown and ideal for larger infestations. Safe for pollinators once dry.
- Bonide Tomato & Vegetable Insect Control Concentrate - Designed for fast knockdown of insects on edible crops—perfect for your vegetable garden.
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Ferti-lome Triple Action (VPG) - A 3-in-1 solution that handles caterpillars, fungus, and mites on vegetables and herbs.