What’s Eating My Dahlias? 8 Pests to Watch For

Aphids are easy to identify and are a reasonably common dahlia pest. They are small (about 1-3 mm long) with soft bodies. They appear in shades of red, green, pink, yellow, black, or green, but they all have similar features. They have long legs and short tubes protruding from their ears, though their size makes it difficult to see.

You’ll find them mainly on stems and the underside of leaves. They congregate in clusters and typically favor new, tender growth. They cause leaves to curl and shrivel, leaving behind honeydew that grows black sooty mold.

It’s difficult to prevent aphids in the garden entirely. But, there are positive practices that keep their populations down. Encourage beneficial insects, such as ladybugs, lacewings, and parasitic wasps. They all like to feed on aphids. Avoid overfertilizing, as they prefer the tender new growth that excess nitrogen produces.

Physical removal is effective. A strong stream of water will knock these off your plants. But dahlias can be sensitive, so this isn’t always the best idea. If the infestation is small, wiping them off by hand is also effective. Neem oil and insecticidal soaps will eliminate them. However, these are not good for pollinators, so avoid using them near or on flowers.

Encouraging beneficial insects is a great, natural way to control these in the long term. Plant a wide diversity of flowering plants to bring them in.

Spider mites are tiny, so they are difficult to spot. You may see their fine webbing on the undersides of leaves or in the petioles. Signs of infestation include stippling on the leaves, tiny yellow or white dots. Dry foliage with yellowing or bronze discoloration is another sign.

Humidity is a spider mite’s enemy, so moisture is the best prevention. Keep your plants well-watered and healthy, and mist the foliage from time to time. This is helpful during dry spells. It’s important to maintain proper spacing and air circulation.

Spider mites have many natural predators. You can attract these predatory insects with nectar-rich flowers is a great way to combat these pests. Neem oil, horticultural oil, and insecticidal soap are also effective treatments.

Thrips are tiny, so they are difficult to spot. They leave silvery or bleached streaks on leaves, and you may be able to identify them by their droppings. They leave tiny black specks behind, often on the back of leaves. Curling or deformed leaves, buds, and flowers are another sign of their presence.

Keep your dahlias healthy, and inspect them regularly. You can use neem oil as a preventative, but the best defense is beneficial, predatory insects. Attract these with nectar-rich flowers.

Yellow sticky traps are highly effective against thrips, but also have potential to harm beneficial insects. They are attracted to the color, and then they stick and can’t pull away. Neem oil is an effective treatment for an infestation.

Caterpillars are typically easy to see. They’re slow-moving and spend most of their day eating. If you notice chewed-up leaves and small, pellet-like droppings, they are the most likely culprit.

Armyworms are a bit more difficult because they are tiny and their damage has a different appearance. These little caterpillars work in large groups and eat the tissue of your leaves, leaving behind a brown, lacy skeleton.

Caterpillars are tricky because their adult counterparts typically fly, and they lay eggs where their young can feed. It’s difficult to prevent this. Physical barriers are great for these and a few other insects that ruin your flowers. I use organza bags to cover my flowers. This keeps them perfect for cutting.

Because they are easy to spot and typically localized, hand-picking is an effective way to eradicate these dahlia pests. Attracting predatory insects can help keep populations under control. You can also apply Bacillus thuringiensis, which is a natural bacterial insecticide. It’s toxic to caterpillars, but won’t harm pollinators.

If you’re not familiar with these by the name earwig, they’re also commonly called pincer bugs. They’re about a half-inch long, dark brown, and have scary-looking pincers on the front of their heads.

The damage they leave is usually on the flowers. They will chew on the edges of petals, leaving jagged tears and holes. They may also chew on the foliage, but typically close to the ground, where it’s not noticeable. Their damage happens overnight.

These pests are the real reason I use those organza bags on my blooms. They destroy flowers, which is sad, but they eat other nuisance insects, so they are good in that way. Covering the buds with these bags allows the flowers to bloom and keeps out pests that would chew them up.

Diatomaceous earth sprinkled around the base of the plant is generally a good way to ward of crawling insects. You can remove them manually, or create barriers with sticky traps or tape around stems to prevent them from climbing.

Handpicking and trapping are the best methods of elimination. Fill shallow containers with vegetable oil and soy sauce. Place them near your dahlias overnight. The earwigs will climb in and drown.

Slugs and snails are larger pests, and you can typically spot them if they are present when you’re examining the plant. However, they tend to feed at night, so you may only see the ragged holes they leave and their slimy residue left from the night before. They may completely chew off the young shoots.

Snails and slugs tend to hide in thick layers of mulch and other debris, especially when the ground is wet. Keep the ground clear under your dahlias to keep these pests at bay. You can sprinkle diatomaceous earth or eggshells around the base of plants to keep these and other soft-bodied pests away.

Hand-picking works if you can find them; it’s best to do this at night or early morning. Just pick them off and drop them in a bowl of soapy water. Beer traps are also effective. A shallow dish, buried at soil level and filled with beer, will attract them. They will fall in and drown.

Look for pale stippling or speckles on leaves. It shows up mostly around the veins. The leaves may have a scorched appearance and appear yellow or brown. They may also appear faded. Severe infestations can result in curling and distorted foliage.

Avoid overfertilizing your dahlias. Excess nitrogen attracts these and other sap-feeding pests. Floating row covers are effective, but can be challenging to work with. Encourage beneficial insects that feed on leafhoppers and their eggs.

Some sources will say that you can spray these off with a strong stream of water, but they’re likely to return. Insecticidal soap and neem oil are both effective against leafhoppers in their nymph state. You’ll want to repeat this treatment at intervals of five to seven days until they’re eradicated.

These pests are easily recognizable by their coloring and that distinctive triangle marking on their back. Signs that they are present include blackened or distorted flower buds, brown streaks on petals, and deformed foliage. Where they pierce the tissue, they inject enzymes to liquify and suck out the sap. This leaves small, sunken spots and necroses at the edges.

Avoid overfertilizing, as these are sap sucking dahlia pests. Encourage beneficial predators, such as damselflies and spiders, to help keep populations scarce. Inspect your plants regularly to catch any issues early.

Remove damaged plant material to deter their return and prevent the spread of other pests. In the morning, you can vacuum them off the leaves, as they are lethargic early in the day. Insecticidal soaps and neem oil are effective treatments against tarnished plant bugs.