Humans aren’t the only ones that love roses! There are many insects and other creatures that enjoy them too, and unfortunately their attention can lead to some unsightly foliage and blooms. The good news is that most situations are manageable once you know what you are dealing with. Take a close look at the flowers, leaves, and canes of your rose and compare what you observe to the notes below to identify your visitor and find the best path forward.
Common Insects
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Aphids - These very tiny, pear-shaped insects, typically around 1 to 2mm or 1/16” in length are typically found in clusters at the base of a flower bud. They come in black, brown, white, yellow, pink, or green and feed on plant sap using piercing mouthparts. While small numbers cause little harm, larger colonies reproduce rapidly and can quickly lead to visibly distorted buds and blooms.
Photo by Gualberto Valderrama on Unsplash
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How to Help: The easiest first step is a strong stream of cold water directed at each infested stem, ideally in the morning so the plant has time to dry. This can be repeated as often as needed. Aphids also have natural predators, including parasitic wasps, ladybugs, hoverfly larvae, and green lacewings. Growing companion plants that attract these beneficial insects near your roses is a wonderful long-term strategy. Insecticidal soap sprays are also effective. Follow the instructions on your product of choice.
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Cane Borers: This is not one particular insect species but rather the larvae of various wasps or beetles that hatch from eggs laid in cut or injured cane tissue. The larvae bore into the pith of the canes, causing it to die back. Evidence includes wilting or dying cane tips, often with a small entry hole visible at the cut end. |
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How to Help: Prune affected rose canes 2.5 to 5cm or 1” to 2” below the damage and seal all fresh pruning cuts to help prevent future entry. It is worth noting that many of the wasps and beetles whose larvae become cane borers are themselves highly beneficial in the garden, so reaching for insecticidal sprays is worth considering carefully. |
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Caterpillars or Rose Slugs (Sawfly Larvae) - Caterpillars are the larvae of a butterfly or a moth and occasionally find their food source on your garden roses. Rose slugs, while mimicking the look of a caterpillar, are not truly being part of this category. Both target rose leaves and are identified the same way. Signs of their presence include irregularly shaped holes in leaves or leaves that seem to be disappearing altogether. Caterpillars occasionally found on roses include the corn earworm and eastern tent caterpillar and vary widely in size. Rose slugs can be tricky to spot as they are often a soft green that blends into the underside of leaves and are typically around 10 to 19mm or 1/2” - 3/4" in length when mature.
Photo by Jurjen Vos on Unsplash of sawfly larvae
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How to Help: There are some differences in the approach to controlling these nuisances though handpicking both caterpillars and rose slugs is a reliable method. BTK (Bacillus thuringiensis kurstaki) is a naturally occurring bacteria that specifically targets caterpillars, though it does not affect rose slugs. Rose slugs can be effectively knocked off with a strong spray of water from the hose. Once removed they are unable to climb back up. Insecticidal soap sprays are an effective tool against rose slugs. |
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Japanese Beetles - These beetles are easily identifiable by their iridescent green and copper colouring. They measure around 10mm or 3/8” in length. Feeding mostly during the daytime, they can be found munching on the leaves of the rose as well as nestled in the bloom. Tell-tale signs include irregular holes in leaves, damage to buds and flowers, and tiny black droppings among the petals.
Photo by Leslie Saunders on Unsplash
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How to Help: Handpicking the beetles off of your roses and dropping them into a bucket of soapy water is effective. An invasive species, Japanese beetles lack natural predators in North America though birds such as starlings, blue jays, robins and cardinals will eat them. Planting seed-producing flowers such as sunflowers or coneflowers will help attract these birds to your garden. Other predators that have adapted to this new species include spiders, assassin bugs and the parasitic tachinid fly.
Some mammals including skunks and raccoons enjoy Japanese beetle larvae found in the soil. Milky spore and BTG Bacillus thuringiensis galleriae are beneficial bacteria that affect only Japanese beetle larvae and can be applied to your lawn in spring or fall. Both of these kill the larvae once it is ingested. Be sure to do some research on these products to find out if they are well suited to your climate and conditions.
Traps made to lure Japanese beetles are also very effective. The downside is the lure attracts more beetles to your area and traps need to be emptied frequently. Neem oil, a natural product, can also be a helpful tool. It can be added to water along with a drop of soap and sprayed liberally over the leaves and blooms several times a week or after a heavy rain. Keep in mind that it will discolour lightly coloured flowers. Neem oil causes the plant to taste bitter, helping to deter insects from taking a bite.
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Leaf Cutter Bees - These bees are similar in size to honeybees around 10 to 15mm or 3/8” to 1/2” and are generally black, sometimes a metallic purple or green sheen. Female bees cut out circles or semi-circles from the leaves to line their nests, leaving the foliage looking as though a hole punch has been at work.
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How to Help: While the damage can look alarming, the effect on the rose is minimal. Leaf cutter bees are valuable pollinators and no control is recommended or necessary. |
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Rose Chafer: Looking similar to a Japanese beetle in size, around 10mm or 3/8” in length, and with its brown and green-coloured exoskeleton, they can be differentiated by their lack of iridescence and its longer spindly legs. It feeds on foliage and flowers, leaving leaves skeletonized and petals riddled with holes.
Photo by Anna Evans on Unsplash
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How to Help: Handpicking is the most effective and recommended method. Rose chafers contain a toxin that is harmful to small birds and chickens, so they have very few natural predators. Beneficial nematodes applied to the surrounding lawn can help target larvae in the soil. |
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Rose Curculio: This is a very small red and black beetle, around 6mm or 1/4" with a distinctively elongated snout that feeds on rose buds, flowers and stems. They are picky eaters giving preference to yellow and white blossoms. Watch for small, circular holes in unopened flower buds and petals. The tips of rose canes may be damaged or girdled, causing drooping with all of this leading to buds drying up, turning brown or failing to open. |
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How to Help: Handpicking is the most effective first step. Beneficial nematode application to the surrounding lawn and garden can help manage larvae in the soil. Creating garden spaces that invite bluebirds, warblers and wrens can be of benefit. Insecticidal soap sprays may also offer some relief. |
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Rose Leaf Hopper: Rose leafhoppers are tiny pale yellow to green insects, around 3 to 4mm or 1/8" in length, that feed on sap from the undersides of rose leaves. They can be tricky to spot as they quickly jump away if disturbed. Their feeding causes stippled mottling on the leaves which may cause them to turn brown and fall prematurely, though they rarely affect the vigour of the rose.
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How to Help: Natural predators including ladybugs, birds, wasps, and certain beetles help keep leafhopper populations in check. Growing companion plants that encourage these beneficial insects to live in the garden is the best option for dealing with this pest. |
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Rose Scale - These are destructive, yet tiny, around 2 to 3mm or 1/16” armoured scale insects that feed on plant sap causing noticeable die back if left unmanaged. Look along the canes of the roses where they appear as small, gray-white, yellowish to brown or black, crusty bumps. Their waxy coating protects adult insects from many insecticides, making them a persistent challenge. Immature insects, called crawlers, are more vulnerable to treatment. |
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How to Help: Small infestations can be scraped off by hand. Cutting away heavily infested canes is effective. Horticultural dormant oil sprays work well and are a good tool for early season prevention. Insecticidal sprays help manage the juvenile crawler stage. Attracting natural predators such as ladybugs and parasitic wasps is often enough to keep populations in check.
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Spider Mites - These mites are incredibly small, less than 1mm or 1/16” and are difficult to see. However, they leave several clues of their presence. Early damage looks like yellow or white speckles on the lower side of the leaf. Fine webbing that collects dirt and debris can also be seen under leaves or around the buds. They are sap suckers, typically feeding on the undersurface of a leaf and sometimes around the flower buds, causing damage to both.
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How to Help: A strong spray of water will knock spider mites off the plant and is a good first approach. Beneficial insects such as lacewings and ladybugs are natural predators, as are certain predatory mite species, which can be identified by their comparatively longer legs. Insecticidal soap sprays can be used with effectiveness as well. |
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Thrips - Thrips are tiny, yellowish-brown insects that have fringed or feathery wings. They are incredibly small at around 1.5mm or 1/16”, making them very difficult to detect. They feed by scraping away surface cells on both leaves and flower petals to access plant sap. This can result in distorted flower buds that may only open partially or not at all. Damage from thrips also can be visible as brown streaks or edges of petals. Young and tender leaves tend to become distorted and are often left with yellow spots due to thrip damage. Lightly coloured roses seem to be a thrips preferred choice. |
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How to Help: Remove and destroy any heavily infested blooms. Keeping grass and weeds trimmed nearby can also be helpful. Insecticidal sprays can be useful but need to be timed correctly, being used before the thrips make their home inside flower buds. Since damage is usually noticed after this stage, it can be difficult to use spray as an effective approach. Hoverflies are a natural predator of thrips and planting companions to attract them can be of great benefit. |
Before you turn to insecticidal sprays to combat some of these pests, consider your fertilizing philosophy. While these products can be effective, they also damage the balance of beneficial organisms and insects in the soil and garden.
Follow all instructions for use and best practices when using sprays and other garden products to ensure your own protection as well as that of the roses, paying close attention to recommended application times of day and climate conditions. Take care not to overuse which can certainly cause more harm than good.
The application of beneficial bacteria and nematodes often requires some specific consideration as well, such as soil type and temperature. Be sure to research these details to see if they suit your needs for pest control and if they are suitable for your climate.
Promoting a well balanced eco-system in your garden is one of the best ways to deal with pests. That balance can be your best long-term defence. A garden rich in biodiversity is a garden that increasingly takes care of itself.
For a list of companion plants that can help deter pests or attract beneficial insects, please see our resource Companion Plants For Roses.
