Why Do My Knockout Roses Get Holes In The Leaves?

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Are you scratching your head, wondering what is causing your Knockout Rose to get holes in the leaves? You are not alone. First, if you find your rose leaves have holes, it’s important to identify the cause and apply the appropriate treatment.

Low-maintenance Knockout rose shrubs are characterized by their cluster of single or double blooms. Knock Outs are incredibly resistant to fungal diseases like powdery mildew and black spot disease (diplocarpon rosae).

Blooming Knockout rosePin

However, many insects and pests enjoy dining and leaving holes on rose leaves. People have noted that their rose bush leaves have holes. 

Which Rose Pests Commonly Feed On Knockouts Leaves?

Many pests and insects chew holes in rose leaves, but some pests are more common than others.

In the warmer months of May and June, a pest called a Rose Slug targets your plant. These pests are larvae of rose sawfly wasps that enjoy feeding on the rose leaf, leaving them transparent.



As rose slugs develop, they may begin to chew large holes in the leaves, eating everything except the mid-rib.

To spot a rose slug, search on the underside of the green foliage when scouting. They are smooth with heads that are a yellow-brown color and translucent greenish-yellow bodies.

Typically, you can drown them in a bucket of soap and water, but you may need to consider a more potent insecticide if you have a heavy infestation.

Close-up of a white rosebud with green leaves against a blurred natural background.Pin
Photo Credit: Instagram @gardenersofthepurplesage

Are Rose Slugs and Rose Sawfly Related?

According to NC State University, the rose sawfly and the rose slug are not the same pests but are related. 

  • The rose slug is actually the immature stage of the rose sawfly. 
  • The adult sawfly lays eggs on the undersides of rose leaves in early spring.

Japanese Beetles

Japanese beetles and caterpillars are two other common pests that can cause leaf holes in roses. If you do not notice rose foliage damage until June or July, you likely have adult Japanese beetles feasting on your Knockout Roses.

Japanese beetle eating rose leafPin

These beetles will eat the flowers and foliage, leaving your plants with a lacy appearance.

Japanese Beetles are fairly pretty bugs. They have metallic green bodies and wing covers that are a shiny bronze color.

The best way to get rid of these knockout roses bugs eating leaves is to handpick them in the mornings and evenings when they are less active.

Using insecticide spray on them is not ideal, as the strength required to kill them is toxic to bees.  

Leaf Cutter Bees: The “Bugs” Eating Rose Plant Leaves

Are you noticing holes in your knockout roses’ leaves? One common culprit behind the holes in rose bush leaves is leafcutter bees.

Though the damage is relatively minor, the cuts in the leaves are unsightly and can be avoided.

These bees are solitary and do not live in colonies, so infestations are not likely. They are crucial to pollinating crops and native wildflowers, so you should avoid using chemical means of control.

Since the damage is minor, consider leaving them alone and allowing them to thrive.

Aphids

Aphids, also known as plant lice. They are typically less than 1/8″ inch long.  Depending on the species, they come in various colors, including green, yellow, red, and black.

The aphid pierces the plant’s tissue with its sharp, needle-like mouthparts. Then suck and feed on plant sap. This can lead leaves to curl, yellow, or develop spots. Over time, this can weaken the plant and stunt its growth.

Aphids feeding on a beautiful rose budPin
Aphids feeding on rose bloom | Lsolmar-DepositPhotos

Additionally, as aphids feed on roses, they excrete a sticky substance known as honeydew. The honeydew can attract other insects and lead to the growth of sooty mold. 

Look for aphids on the undersides of the leaves or on new growth. Given their small size and color variations, they can sometimes be challenging to spot.

NOTE: Releasing beneficial insects into your garden, like ladybugs and lacewings, can help control aphid pest populations.

Rose Chafer

The Rose Chafer (Macrodactylus subspinosus) can cause considerable damage to your Knockout Roses, including holes in the leaves of rose bush shrubs. 

The rose chafer beetle is a light tan or straw-colored insect with long, spiny legs. Rose chafers are particularly problematic during their adult phase, which typically begins in late spring or early summer, coinciding with the flowering period of many roses. 

rose chafer beetle feeding on a flowerPin

They feed on the leaves, buds, and flowers of roses, often skeletonizing the foliage and leaving behind a lacy or hole-filled appearance. 

The presence of these beetles and the unique damage they cause can be alarming, but with the right management strategies, it’s possible to limit their impact and protect the health and beauty of your roses.

Deer

Deer loves roses. Generally, deer will chew on your Knockout Rose plants’ leaves, flowers, and stems, which can severely damage the bush.

If you have deer trouble, the best way to keep them away from your plants is to install a fence. You can also spray the area with deer-repellent spray.

Spraying the plants is a good option because it rarely causes harm to the rose bush and keeps deer away for quite a long time.

How Can I Prevent Pests From Eating My Knockout Roses?

Since these pests are very attracted to Knockout Roses, you need to prevent them from showing up.

Avoid diseases like powdery mildew. Provide your roses with morning sun and filtered or partial afternoon shade.

A close-up of a caterpillar with a black-spotted green body and orange head chewing on a leaf.Pin
Photo Credit: Instagram @cluelessgardenimprovement

In response, it’ll send out lots of new growth and blooms.

Light: These rose varieties grow best in full sun, at least six hours daily or 4 to 8 hours of sun per day. Of course, ensuring you’re also in the correct USDA growing zone is important.

In places with very cold winters, bring the roses inside and store them in a cool, dark area such as your basement or garage.

Pruning

The first thing you need to do is prune your Knockout Roses in the later spring or late winter months to remove all dead growth. Search for canes that tend to rub against each other because these areas attract pests.

Pests on Rose PlantPin
Photo Credit: Instagram @qwerkypix

Prune them in the early spring to the height you want. Foundation planting If you want a variant on the usual boxwoods or other evergreen shrubs,

We also recommend mulching around the area to conserve moisture and prevent weeds from growing.

Constant Examination

Check on your rose bush once or twice a week to keep pests from getting comfortable.

Pick a container with good drainage that is two sizes larger than the pot in which the rose comes in.

A close-up of a person's fingers holding a leaf with holes possibly caused by insect feeding, against a blurred background.Pin
Photo Credit: Instagram @amber_gardenaddict

If you find any pests, fill a cup or jar halfway up with warm water and add a few drops of dish liquid. Handpick the pests and drop them into the pot. If you do this a few times a week, you can control the infestation.

Younger plants need more consistent watering than established roses when they become relatively drought-resistant. Water the roots in the morning to prevent leaves from developing a fungus from wet foliage.

Bacillus thuringiensis (Bt) – A Natural Treatment For Holes In Rose Leaves

Bacillus thuringiensis, (Bt) is a natural soil bacteria used as a biological pesticide. While it doesn’t directly relate to the creation of holes in my rose leaves, it’s a crucial part of the solution.

Bt is very effective against a variety of insects that can cause leaf damage in roses, such as:

  • Japanese beetle
  • Rose chafer
  • Rose sawfly larvae
A green caterpillar on the pink petals of a flower with visible stamens and pistils.Pin
Photo Credit: Instagram @beckyramskogler

The bacteria is toxic to these insects but safe for humans, pets, and beneficial insects. When a pest ingests Bt, the toxic proteins disrupt their digestive system. This causes them to stop eating and eventually die, helping to prevent more leaf damage. It works as a natural insecticide. 

For best results, apply Bt when pests are in their larval stages. It is less effective against adult insects. Regular inspections of your roses and timely Bt applications can help keep these leaf-damaging pests in check.

Foliar Spray

Spraying water from the hose directly onto the areas where insects are heavy will help you manage your problem. Knockout roses are less susceptible to water spots than other roses, so you will not damage them.

Sprays of soapy water, Neem oil,  insecticidal soap, and horticultural oils offer some control. When spraying, cover the underside of the leaves for the best results.

These sprays and systemic insecticides can also help control scale insects, spider mites, and thrips.

More On Caring For Knockouts

Fertilize To Prevent Rose Bush Holes In Leaves

Regularly fertilizing Knockout Rose is a fantastic way to ensure your plants stay healthy and strong.

Apply the mixed fertilizer around the plant base monthly throughout the entire growing season to keep your plant pest-free and healthy.

A close-up of a pale yellow flower with some petals showing small holes, possibly from insect damage, against green leaves.Pin
Photo Credit: Instagram @debzmonk

Stop fertilizing in late summer so the plant will put its energy into its roots to get ready for winter.

On top of their toughness, they’re self-cleaning – which means you don’t need to deadhead them – and they bloom all season long.

Adding Knockouts To Your Landscape

Here’s what you need to know for growing roses, along with ideas on how to use them to add color to your yard, patio, and garden.

  • Knock Out roses can be the utility infielders of your landscape. They can be foundation plantings, border plants, low hedges, or even specimen plants.
  • They’re popular because they’re one of the longest-blooming, lowest-maintenance, easiest care, most pest- and disease-resistant roses out there.
  • Nothing makes a garden look as festive or scent the air so perfectly as a blooming rose bush or a fence row covered with cascading shrub roses.
  • It’s tough, grows in almost any well-drained soil in a sunny spot, and doesn’t need spraying for black spot fungus—a common affliction for roses.
  • When insects and pests feast on the leaves of a Knockout Rose, the plant can end up with unsightly holes in the leaves that need to be dealt with.

But they are susceptible to the rose rosette, a virus spread by eriophyid mites that blow in on the wind.

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