11 Dahlia Pests: How to Identify, Prevent, and Treat Them

Dahlias are beautiful flowers, but there are many pests that love to try to ruin even the most perfect flower gardens. In this article, certified master gardener Liz Jaros looks at the most common pests your dahilas will encounter this season. She also walks through how to identify, prevent, and treat each one of them.

dahlia pests

Bursting with pride as you drift through the dahlias you’ve so lovingly nurtured, your heart falls when something unsightly catches your eye near the garden gate. It might be a mottled leaf or a shredded bloom. It might be a sticky web or a broken stem. Your dahlias are clearly under some kind of attack from some type of pest, but from what?

Where there are flowers, there will be pests. And this is particularly true for dahlias, which are highly attractive to insects and critters. From aphids, to snails and slugs, there’s plenty of different harmful creatures that you’ll need to watch out for if you want to keep your dahlias blooming all season long.

Knowing what to watch for, how to identify them, and how to get rid of them is crucial to growing beautiful dahlias in your garden. Here we look at 11 of the dahlia’s most common pests and determine the best ways to send them packing.

Snails and Slugs

Snails and Slugs
In hot and dry weather, snails hide in secluded places in the garden, where it is always dark, cool and humid.

Yellow leaves with irregular shaped holes or shredded margins typically indicate that slugs or snails have made themselves at home in your dahlia patch. The presence of a slippery mucus trail helps distinguish these guys from other chewing insects. If you suspect snail/slug damage, take a flashlight out to the garden at night and examine the undersides of your leaves. You’ll likely see something that looks like a slimy foot creeping around.

Dahlias are most at risk to these pests early in the season when foliage is tender and easily munched, so it’s important to get out in front of snails and slugs. As always, prevention is the best practice for pest problems. Irrigation methods that soak the earth beneath your dahlias and keep leaves as dry as possible will deter slugs, since they require moisture for mobility. Tidy garden beds that are free of spent blooms and hiding places are also a less hospitable environment.

Once you’ve identified them, however, you’ll want to get them out before they can wreak any more havoc. You might have some luck with traps (a cup of beer or soda sunk beneath soil level) or deterrents (coffee grounds, egg shells, chives, mint, or garlic). You could also try working some copper flashing or screening into your garden scape, since copper often interacts negatively with their nervous systems.

A spinosad-based product like Sluggo can also work, but be careful with more powerful insecticides since they may kill beneficial insects as well. Sometimes the most effective way to rid your dahlia beds of snails is through diligent observation and hand picking or heavy spraying with the hose.

How to Identify

Yellowing leaves with chew holes or munched margins and a slimy trail will indicate the presence of snails and slugs.

How to Prevent

Keep beds tidy and free of hiding places. Use soaker hoses to water so leaves remain dry. Copper garden elements can also deter these pests. You can also plant dahlias in containers that are harder for slugs and snails to climb.

 

How to Remove

Try beer traps, hand removal, deterrent plants, hose spraying or slug killer.

Aphids

Aphids
If single colonies are found on dahlias, then they just need to be cut with leaves.

Yellow, distorted leaves and a sticky black substance on your dahlias might be an indication that aphids have settled in. These small sap sucking insects can come in an assortment of colors but they are typically green and pear shaped with long legs and antennae. They can do a lot of damage and harbor disease, so it’s important to address them promptly.

Pesticides are typically less effective than natural techniques for discouraging aphids and often cause more harm than good by killing beneficial insects. You can try spraying a hard stream of water on the undersides of leaves, where aphids congregate, or coat leaves with a horticultural oil.  Introducing predatory insects like ladybugs and lacewings to the garden can help keep the population down. You can also companion plant your dahlias. Garlic, chives, nasturtium and catnip can also be effective in repelling aphids.

The best way to prevent aphids from becoming a major headache in the dahlia garden is through careful monitoring. Catching the problem early is crucial to elimination.

How to Identify

Found in green, brown, red or black with pear shaped bodies and long antennae, aphids will give you distorted leaves and secrete a sticky honeydew substance that often attracts ants. Look for them on the undersides of leaves.

 

How to Prevent

Keep beds clean and remove weeds promptly. Monitor nearby plants for infestation.

 

How to Remove

A strong spray with the hose, aimed specifically at the undersides of leaves will knock them off. Horticultural oil and hand removal are also effective. Predatory insects like lady beetles and parasitic wasps can help.

Thrips

Thrips
Thrips usually settle on the underside of shaded leaves and suck the juice out of them.

Long and slender with two pairs of wings and body colors that range from transparent to black, these pests will leave little black puncture wounds on your dahlias’ leaves and create a stippled, yellow pattern. They may also leave you with pale or dropping petals.

When thrips are suspected, try forceful hose spraying several times a day. Or coat leaves with neem oil. Parasitic wasps, lacewings, and mites can all help control a thrip population, so insecticides will likely cause more harm than good when it comes to thrips. Prune off infested foliage as soon as thrips are identified.

Reflective mulch that includes flashes of silver or gray can be used to deter some flying pests, and as always, choose cultivars that are known to be pest resistant. A light mesh covering can also be effective, but not exactly what you want to look at in the dahlia garden.

How to Identify

Transparent to black bodies are long and slender with two sets of wings. Damage includes black puncture wounds and spotted yellow leaves.

 

How to Prevent

Reflective mulch, resistant plant choices, and careful monitoring will discourage infestation.

 

How to Remove

Neem oil, forceful hose spraying, prompt pruning and beneficial predators will help control thrips.

Spider Mites

Spider Mites
Spider Mites are one of the most dangerous dahlia pests. They carry diseases from plant to plant and inhibit their development, leading to death.

Tiny, fast-moving bugs with pale bodies are usually spider mites. Under a magnifying glass, you’ll see red eyes and 6 or 8 legs, depending on age. Mottled yellow leaves that curl up and have a sticky web presence are typically an indication that mites have moved in.

Mites typically work from the ground up, so removing the lowest leaves from your dahlias can help discourage an upward spread. Applying horticultural oils or soaps on the undersides can be effective as well. Plants that are overrun with mites should be destroyed to prevent spread. Mites are attracted to dry, stressed foliage, so keep your dahlias well watered, especially during times of drought.

How to Identify

If webs are present, use a magnifying glass to look for fast moving, pale colored spiders with red eyes. Leaves will appear mottled and dry.

 

How to Prevent

Keep dahlias moist and keep beds free from dust. Monitor nearby plants carefully for infestation.

 

How to Remove

Swift, aggressive pruning and hand shaking will help decrease populations. Oils and soaps can be used with some success. Insecticides not recommended.

Leafhoppers

Leafhoppers
Leafhoppers suck juices, and not from the petals, but from the dahlia stems.

Often confused with aphids, leafhoppers move faster and jump sideways. They can be bright green or camouflage in color, and they have red-tipped antennae and wings. Stippled, pale leaves may curl or drop off if leafhoppers are feeding on them. They may also leave black spots behind.

Because they are fast moving, leafhoppers are difficult to control. While they can occasionally harbor disease, most pose a relatively low threat to overall plant health. Damage from them can be unsightly, though, so they should be discouraged from settling in.

Remove faded blooms and foliage promptly from beds to eliminate shelter spots, and remove plant tops completely at the end of the season to discourage overwintering. A narrow range oil applied on the undersides of leaves can also reduce leafhopper numbers.

How to Identify

Look for these fast, slightly larger (up to ¼ inch) pests with red tipped antennae and wings. They will be hopping sideways on stippled, pale or curling leaves with little black spots.

 

How to Prevent

Spiders, lacewings and lady beetles are all leafhopper predators. Allowing these insects free range in our dahlias is good prevention. Keep garden beds tidy and free of debris in winter.

 

How to Remove

Forceful hose spraying and predatory insects can help reduce numbers. Oils can help discourage clinging to undersides of leaves.

Earwigs

Earwigs
Earwigs damage plants at night, gnaw holes in leaves, eat flower petals and growing shoots.

Damage from earwigs is usually signaled by shredded blooms and munched older leaves. Easy to identify because they are large (comparatively) and have rear pinchers that look like forceps, earwigs can do a lot of visual damage to dahlias. They are not typically life threatening, however, and they do control both aphid and mite populations efficiently. So their management should include reasonable attempts to keep them in check, without going overboard.

The key to discouraging earwigs lies in habitat management. Since they prefer dark, moist places to hide, keeping dahlia beds free of rocks, yard art, dense groundcover, and debris is a good place to start. You can also set traps using wet newspaper stuffed in toilet empty toilet paper rolls to lure earwigs away from your blooms and foliage. Chickens and toads both feast on earwigs, so they should be given free range in the dahlia garden when possible.

How to Identify

Adult earwigs are typically ¾ inch long and dark brown, with rear pinchers that look like curved forceps. They are particularly active at night. Leaf and petal damage will look like large bite marks.

 

How to Prevent

Reduce moist hiding places and don’t surround dahlias with groundcover or heavy mulch.

 

How to Remove

Introduce some chickens or toads as natural predators and keep beds free of rocks and natural earwig shelters. Set newspaper traps.

Caterpillars

Caterpillars
Caterpillars are usually found on inflorescences only when the blossoming inflorescence is disfigured.

In their larval stages, moth and butterfly caterpillars can do a lot of damage in the dahlia garden. Larvae have three pairs of legs behind their thorax. Leaves damaged from young caterpillars will often look like holes have been punched in them. Rolled leaves held together by webs are also tell-tale signs of caterpillar habitats.

Caterpillars can destroy dahlia seedlings, stems, and buds very quickly. Vigilant monitoring and hand picking will likely be your greatest weapons against them, but some management can also be done with microbial insecticides and predators (wasps, spiders, birds). Reflective mulch can be used to discourage them from settling in, as they find it disorienting. And stay on top of weeds.

How to Identify

Caterpillars are worm-like and green to brown, with three pairs of legs behind their heads. Damage includes chew holes and rolled, webbed leaves.

 

How to Prevent

Reflective mulch, weed-free beds, and bird-friendly environments will help prevent infestations.

 

Hot to Remove

Hand pick caterpillars and drop them into sudsy water. Purchase predatory wasps. Leaves can be coated with microbial oil as soon as caterpillars are identified.

Deer

Deer
Dahlias are herbaceous plants with carbohydrates, minerals and sufficient moisture that is useful for deer.

Since deer are opportunistic feeders and not particularly discriminating, they will eat dahlias if they happen upon them. Deer get carbohydrates, minerals and moisture from herbaceous plants, and dahlias can deliver all of those things in spades if well cared for.

Many dahlia varieties will reach heights within a deer’s browsing line (1-4 feet) and are very physically attractive, which makes them perfect targets. Look for shredded leaves and blooms to indicate the presence of deer, and watch for late night or early morning feeding sessions.

Habitat management is usually the best way to combat deer. Perimeter fencing at a height of 6 feet tall will usually do the trick, but is not always practical or possible. Dahlia devotees swear by bubble wrap, stinky shoes and human hair as deer deterrents, but some of these tactics can be more disturbing than chewed leaves and may require more time than you actually have on hand. You can also cover your plants each night with a tarp or hard container, but again, you’ll need to weigh the results against your commitment and sanity.

How to Identify

Look for shredded or rough-chewed leaves and blooms about 1-4 feet from the ground. Deer have no upper teeth and must twist and pull the plant parts they’re eating. Watch for deer late at night and early morning (when they typically feed) to confirm your suspicions that they are doing the damage.

 

How to Prevent

Property fencing and garden fencing are your biggest weapons against deer.

 

How to Remove

Keep an eye out for deer late at night and early morning. Shoo them away with loud noises and/or bright lights. They might move on to someone else’s garden if feeding in yours becomes more trouble than it’s worth.

Rabbits

Rabbits
Rabbits can leave chew marks on dahlias between 2 inches and 1 foot above the ground.

If stem breakage and chew marks fall somewhere between 2 inches and 1 foot above ground, rabbits are likely to blame. Look for clean, 45 degree cuts in your dahlias’ stems as well as ¼ inch pellets in the vicinity. Generally speaking, if you have a rabbit problem, you’ll know it.

As rabbits typically graze near an escape cover, keep your yard free of clutter and seal off access points to sheds, garages and porches. Keep bird feeders away from dahlia beds and consider some kind of mesh fencing if rabbits are doing major damage. Remember that fences need to be partially buried and at least 18” tall if they are to be effective at rabbit prevention. Some success might also be had using strong odors like garlic, ammonia, and cayenne pepper to turn them away.

How to Identify

Look for clean stem breakage at 45 angles somewhere between 2 inches and 1 foot above ground and watch for pellets.

 

How to Prevent

Reduce junk and clutter in the yard, so rabbits will have few hiding places. Let dogs and cats roam freely to encourage rabbits to graze elsewhere. Install sub-grade mesh fencing to keep them out.

 

How to Remove

Trapping and poison can be used to remove rabbits from your property if certain conditions are met. Check with your county for rules and regulations.

Voles

Voles
Voles like to build their nests at the base of trees and shrubs, which can damage the roots, especially because these rodents love to chew on bark.

A little closer to the ground, if you notice gnaw marks on your dahlias’ roots or stems and tiny burrows in your mulch, you might be dealing with voles. These compact rodents have gray to brown fur, short bushy tails and hidden ears. They measure between 5 and 8 inches long from nose to tail.

Heavy vegetation is attractive to voles for protection and shelter, so keep your dahlia bed and adjacent gardens as lightly dressed as possible if you suspect voles have moved in. Do not keep grass or leaves piled nearby, and be diligent with weeding. Mesh or wire fencing buried at least 6 inches below ground level can help to physically exclude voles from your dahlias. And if you feel like the population is out of control, baits and traps can be used effectively to reduce their numbers.

How to Identify

Chew marks near your dahlias’ roots or stems and slow flower production are symptoms of vole damage. Look for gray to brown rodents with short bushy tails.

 

How to Prevent

Keep leaf and grass piles as well as dense groundcover patches away from dahlia beds. Bury mesh fencing 6-8 inches below grade to block voles out.

 

How to Remove

Baits and traps as well as predatory animals like cats and hawks can help address small populations.

Squirrels

Squirrels
Squirrels dig up and damage the bulbs of ornamental bulbous plants, eat bark, young shoots, buds and flowers on trees, and also eat food from bird feeders.

If you’re finding dahlia roots in places where you didn’t plant them, you may have a squirrel problem. These furry nuisances can do a great deal of damage before your dahlias have even had a chance to grow. Look for holes in your beds and pieces of root here and there, particularly in fall.

A squirrel typically forages within 75 feet of its home, so they tend to build burrows and nests near homes with bird feeders and seed/nut sources. Eliminating these opportunities from your yard will encourage them to move elsewhere, but it will also send the birds packing.

Fumigation, live trapping, shooting, and baiting can also be done to address extreme squirrel infestations, but nothing is likely to shut down the party completely. Pepper spray, mint plantings, loud noises, and bright lights may have some deterrent effect.

How to Identify

Holes in the garden, scattered root parts, long ground burrows, and missing plants are all signs of squirrel presence.

 

How to Prevent

Look for old burrows and destroy them completely to prevent new squirrels from moving in. Eliminate bird feeders and water sources from your yard. Motion lights, loud noises and sprinkler systems are also unfriendly to squirrels.

 

How to Remove

Scare them away with loud noises and natural predators like dogs and cats. Baiting, trapping, and fumigation strategies can be employed if your squirrel problem is severe.

Final Thoughts

No garden can or should be completely free from bugs and animals. They are all a part of a balanced ecosystem that welcomes some predatory behavior into the mix. What’s important to remember is that moderation is always the ultimate goal. Keep your eyes sharp and your identification skills up to date, and be ready for some trial and error. You should find that most pest-related problems can be handled in a way that keeps your beautifully colored dahlias popping and your unwelcome tenants under control. 

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