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

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

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.

Aphids

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.

Thrips

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.

Spider Mites

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.

Leafhoppers

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.

Earwigs

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.

Caterpillars

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.

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.

Rabbits

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.

Voles

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.

Squirrels

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.