Green worms on roses

Q: My Knockout roses are pretty hardy, but something is decimating them, right down to the veins. There are little green worms, maybe caterpillars? They are coiled into a C shape, and there are several on each branch.

A: You have rose sawflies. The leaf damage looks a bit like Japanese beetle feeding but if they were the culprit you’d see lots of them feeding on your roses.

Sawfly larvae are much more inconspicuous. They feed from the bottom of leaves and they are only out in early morning…so gardeners have a hard time seeing them. You’ve done a good job catching a picture.

The sawfly larvae LOOK like caterpillars to the uneducated eye but they are not. A sawfly is a primitive wasp-like insect. The females have a saw-like blade at the tip of the abdomen that is used to cut slits into plant tissue into which they deposit eggs. The resulting larvae feed voraciously. But since they are not caterpillars, they are not affected by the organic caterpillar insecticide, B.t. (Dipel, Caterpillar Attack, etc)

Organic insecticides such as or those containing l are effective as long as you apply them under the leaves when the larvae are present.

The contact insecticide ) offers good control if sprayed on the whole rose. ) is a systemic which can be applied to the soil around the roses in spring before feeding activity is noticed.

Sawfly Identification

sawfly damage

European rose slug (sawfly)

sawfly damage

curled rose slug (sawfly)

Tags For This Article: rose slug, roses, sawfly

Sawfly larvae resemble a caterpillar but are actually the larvae of the sawfly, a wasp-like flying insect.

I always say that roses are like the chickens of the plant world: everything wants to prey on them. In my garden, there are three recurring pests that I have waged war on, and one of them is the sawfly larvae, or commonly known as “rose slugs.” Appearing sometime in May, just as the roses are starting to look amazing, the sawfly larvae chews it’s way through buds and tender leaves, and left unchecked can completely skeletonize it in just a matter of days. Sawfly larvae are so tiny that they you will see the damage they create before you actually see the culprit.

I’ve found that early identification is the best way to manage this pest. In mid to late spring, check your rose leaves and buds for tiny holes indicating that the larvae are present. Flip the leaves over where you are sure to find at least one chomping larvae, and gently pull back the calyces (the leaves protecting the bud) to find the larvae nestled within making breakfast from your rose petals. And then squish them! Spending just a few minutes a day on each rose bush checking and squishing is an effective and organic method of control.

Sawfly larvae love the tender new leaves of a rose. If you look closely you can see some larvae still present on some of the leaves. This picture was taken pre-squish.

Severe infestations can be managed with chemical controls (like Sevin), but I don’t recommend them. One, because I shy away from them myself and so how could I recommend something I don’t use? And two, because certain pesticides will also eliminate beneficial insects (and birds) which, trust me, you want in your garden. I’ve recently begun using a very watered down Neem Oil (derived from the seeds of neem trees) on my roses to help control the fungal disease, black-spot. Neem oil is also effective against pests over time, but, because it is an horticulture oil, can suffocate beneficial insects as well. It is best applied in early morning so the leaves have time to dry before the beneficial insects begin working, and like anything should be used with caution and restraint. In other words, just because something says it’s organic doesn’t mean it’s safe in all aspects. For more information on Neem, click here. EDIT: This summer I’ve stopped spraying my roses at all. Yup, not one bit–not even the organic horticultural oils to control black spot because I’m editing out roses that need coddling whatsoever. And as far as controlling sawfly larvae I still feel the best method is just to squish the ones you find and let the birds take care of the rest.

Sawfly larvae damage on a rose bud. Gently teasing back the calyces will reveal the larvae and allow you to give them a good squishing.

The next rule of thumb is true for any pest/disease management of roses: Keep the area around each plant clean and free of debris such as dropped leaves (especially if they’re dropped because of a fungal disease) and provide good air circulation around each plant. Additionally, remove any damaged/diseased canes and leaves and dispose of them (not in your compost pile!) Roses will also manage better if they are not grouped together but planted among other perennials, annuals, herbs, etc which supply beneficial insects and birds with cover and food. And last but not least, a stressed rose is more susceptible to disease and infestations, so keep them healthy and happy to give them the strength they need to fend off the baddies.

A ladybug larvae hard at work on a Dr Huey rosebud. Ladybug larvae, like adult ladybugs, eat damaging, soft bodied insects like aphids and sawfly larvae.

Early detection, handpicking and destroying the larvae, and encouraging beneficial insects are 3 great ways to protect your roses from sawfly larvae. If you have insects such as green lacewings and ladybugs already present in your garden consider yourself lucky and don’t interfere with their work. Praying mantis are also great for pest control, but keep in mind they will eat anything, including each other, beneficial bugs, and even, I’ve heard, hummingbirds. (Yikes!) Encourage birds, yes chickens included, into your garden as they will also eat nasty pests. I’m going to write a post later on as to how to encourage songbirds into your garden, but the number one thing I’ve found is to provide a year-round fresh water supply. More on that later.

Abraham Darby

So there you have it! Spending a little extra time with your roses each day will help prevent this nasty pest and keep your plants healthy, happy, and looking their best!

EDIT: 7/10/11 In our garden, the roses that I pruned back weeks ago to encourage a second flush of blooms are covered in new growth, and, you guessed it, sawfly larvae. This is round 2, but I’m ready. Don’t forget to periodically check your roses, paying special attention to the tender new leaves and buds. 🙂

About Hedgerow Rose

Laurie Lewis is a gardener, consulting rosarian, writer and photographer currently creating a new garden with her husband, 3 cats, 1 dog, 2 beehives and 5 chickens. View all posts by Hedgerow Rose

Not a Slug, Not a “Worm”—it’s a Sawfly!

Q. My roses are being decimated by little green worms. Some new branches have no leaves left at all. After a bit of research I found out they are sawfly larvae; I can’t find any mention of them on your site. Other websites suggest wildly different ways of dealing with them; and some say that they will eventually go away on their own (as flies, I assume). But will there be anything left of my roses at that point? Thanks,

    —Kathy in North Philly

Every spring for the last ten years, some kind of fly or bee inserts an egg into the new soft growth of my hybrid tea roses. It hatches quickly and the larval stage proceeds to spiral downward through the tissue, girdling it. The end result is a drooping, and soon dead, cane. By carefully slicing the damaged portion open I have found the larvae. Is it a sawfly? A rose slug? It’s about an eighth of an inch long. Pyola seems to help. Any other suggestions? Thanks,

    —Steve in El Portal, CA

For the second year my mugo pines and black pines have been beset by Sawfly larvae. They appear as small green caterpillars that cluster around the tips of the new ‘candles’ and quickly strip the life from the area. They also have the curious behavior of waving in unison when disturbed. How can I rid my pines of these pests?

    —Roy; just outside Lambertville, NJ

Little green worms are decimating the leaves of my roses; and squishing just isn’t keeping them under control. I did some investigation and have concluded that they are rose sawflies. Two sources say that Bt won’t get rid of these little buggers. Is there a treatment that will—but not harm beneficial insects at the same time? Thanks,

    —Pamela in Asheville, NC

A. Sawflies are just plain weird. The larvae sometimes resemble a slug, but more often they look exactly like caterpillars (apparently you have to count the number of ‘prolegs’ to know for sure; sawflies have more of the creepy little things than caterpillars). But these pests are neither slug nor butterfly-to-be; their adult form is a primitive non-stinging wasp that’s been around for millions of years.
Sawfly larvae are known for attacking roses, and for doing so every which way—some types tunnel into the stems, some skeletonize the leaves like Japanese beetles, and others are ‘leaf rollers’—they curl a big leaf around themselves to hide as they chew away. But roses are far from their only prey—there are a large number of different species and they are pestiferous on a wide range of plants. (The pine sawfly is an especially pesky member of this family.)
I’ll bet that some of the “caterpillars” I’ve seen on my roses over the years have actually been sawflies. And pity the poor organic grower who sees what certainly appears to be a pest caterpillar chomping away and, in response, sprays the safe and natural organic caterpillar controller, Bt, over and over—to no avail. Because it don’t matter how much you LOOK like a caterpillar, you have to actually BE a caterpillar to be done in by Bt.

Most experts feel that the feeding done by these pests is indeed ‘self-limiting’; that is, they tend to disappear before extensive damage can be done. And, of course, strong plants that are fed organically, have lots of airflow, and aren’t mulched with wood or watered to death stand the best chance of perking right back up after the sawflies…well, eh—fly.
Different types of sawflies go through different life cycles, so if you have a plant they’re being persistent about season after season, read up on your exact foe. Many kinds can be controlled by cultivating the soil at the base of attacked plants at the right time of year to destroy their overwintering forms. Cleaning the orchard floor at the end of the season is essential to controlling the kinds of sawflies that attack apples and other fruits (and it prevents lots of other problems as well).
When ANY kind of tree is the target, hang suet feeders from the branches over the winter to attract chickadees and other birds that specialize in eating such pests. If your sawfly foe overwinters in parts of the tree—like inside some pine needles—spray dormant oil on the trees in the dead of winter. In warmer months, use a lighter-weight ‘all season’ horticultural oil. (The product mentioned by one of our listeners, Pyola, is a lightweight horticultural oil with a small amount of natural pesticide added.) If you actually see the pests being active on or in trees or shrubs, prune out and destroy the infested branches as early in the season as possible.
On roses and similar plants, handpick the pests, spray them off with sharp streams of water early in the morning (knock them down and they can’t get back up), or spray neem or one of the new spinosad products. You can spray either of these low-toxicity pesticides on the leaves or directly on the pests; but don’t spray any on the flowers or you could hurt bees. In fact, if a rose bush is covered with flowers and sawflies, harvest all the roses for cut bouquets and then spray to kill the weird little wasps. You’ll get rid of the sawflies and encourage a new set of blooms to appear quickly.
When you use Pyola and/or other lightweight horticultural oils, spray directly on the pest to smother them. Same with insecticidal soap. If you do choose soap, spray first thing in the morning and then rinse the plants off an hour later—just to make sure the soap residue doesn’t damage any leaves if the day turns blindingly hot.

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Update: I’m pinning post this to the top of the page because this can be such a frustrating problem. The rose slugs (aka rose sawfly larvae) seem to be worse some years than others an it’s still a little early and cool for the bugs to show up, but when they do come here’s what you need to do.

Summer garden doldrums — I’ve noticed that I’m a little less enthusiastic in my garden lately. I’m pretty content to wander about doing nothing more than a little grooming here and there. But that’s all right because besides deadheading and keeping the garden tidy there’s not that much to do. The exception is keeping a sharp eye out for garden pests, because the sooner you deal with them the better off you’ll be. One of the pests that bedevils us this time of year is the rose slug.

Rose slugs are tiny, green worms that are the larvae of the rose sawfly. Heaven knows why they’re called slugs. They don’t look like a slug and they don’t leave a slime trail. Both the name and their appearance cause a great deal of confusion when you want to find a way to get rid of them. The most important thing to remember is that rose sawfly larvae are not caterpillars and you’ll see why this is an essential bit of knowledge in a minute.

When you’ve got rose slugs, you know it. These little creepies will skeletonize your rose leaves seemingly overnight (they don’t eat the buds or flowers) — one day you’ve got beautiful green, glossy leaves and the next day the plant looks like it was hit by a bomb. It is not pretty!

In Southern California the rose slugs have hit in a big way in most of my neighbor’s and client’s gardens. They are voracious and can make a mess of a rose bed in just a few days. As with most garden pests it’s important to treat for them as soon as you notice any leaf damage. Here, following the principles of Integrated Pest Management, are methods of control in ascending order of potency and potential harm to the beneficial insects in your garden.

Remember that the rose slug feeds on the underside of the leaf, so this is where to look for them and where to spray.

Mechanical

  • Search & destroy — a great release for your aggressive tendencies. Flip rose leaves every morning and squish, or pick off the little worms. Not for the squeamish. This method can work, but you’ve got to be persistent and if you’ve got a big infestation this is a stopgap at best. So the next step is…

Sprays

  • Water — this is a safe and effective method for many garden pests (works especially well for aphids). Dislodge them with a strong stream of water. Frankly, I haven’t found this to be effective for rose slugs, but it’s worth a try.
  • Insecticidal soap. You should spray in the early morning or in the evening when the wind is calm so that you don’t get drift and it won’t harm the good bugs who are not out and about at these times. Aim your spray on the underside of the leaves, it needs to hit the bugs to work.
  • Neem Oil works by suffocating the pest, so be sure you cover the underside of all the leaves.
  • Spinosad works by excitation of the bug’s nervous system. It must be ingested, so it affects only chewing and sucking insects. That said, be aware that it is toxic to honeybees for 3 hours, so spray in the evening when bees are back in the hive. It will take a couple of days to see any results and you may have to spray more than once.

Now for the bit about sawfly larvae not being caterpillars. The reason this is important is that it means that Bt (Bacillus thuringiensis) will not work. I can’t tell you how many times otherwise knowledgeable gardeners have recommended Bt for this problem. Even our local nursery swore that it would work. It won’t and you’ll be wasting your money if you use it for this purpose.

If you have exstensive leaf damage it might stress your plant, but it’s not fatal. Simply strip off all the leaves and they’ll grow back again in a few weeks. Also, it helps to know that if you’ve just planted some new rose bushes this year they were probably raised in a nursery using non-organic methods. The transition into an organic garden will make them more susceptible to pests than your other plants for the first season. Don’t despair, just give them time to get adjusted.

Here’s where I extol the benefits of organic gardening — again. Boosting your soil with compost and feeding your plants with rose tea (click here for the recipe) will make them healthy enough to resist most pests. And organic gardens will attract all kinds of good creature who will help you with your gardening — beneficial bugs and birds especially. (Every afternoon the birds come by to pick bugs off my plants.) So I’m not aiming to have a completely pest-free garden. After all there needs to be a little bit of bad stuff to feed the good guys.

Here are a couple of remarks from Larry Sherk on my column about wisteria in the Feb 6 issue of Globe Real Estate: “It is correct that wisterias raised from seed often take 12 years or more before they start to flower, if at all. Most wisterias sold today are named cultivars and these often flower in the two- to three-gallon containers that they have been grown in and the ones in which they are being sold. Two of the best cultivars for areas in Zone 5 are Lawrence and one called Aunt Dee, which came from Bailey’s Nursery in Minnesota.”

Thanks, Larry.

Q Three years ago I noticed a problem with some of my rose plants. Small, green caterpillars had burrowed into the under-portion of the buds, eating the inside; there was also a trace of web-like material on the outside. This caterpillar is in abundance in the spring.

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I have many varieties of roses, but only some of them are affected. Among the rugosas, species, hybrid perpetuals, galicas and portland, the first productions of buds are almost all killed. Teas, floribundas, grandifloras, English, some climbers and others weren’t affected, or very little.

Last spring, I sprayed with Trounce insecticide when I noticed the web, but it was too late. The rugosas didn’t like the spray, resulting in leaf drop and some dead branches. What is this caterpillar, and what can I do to prevent the same problem this spring?

J.M., Toronto

A This sounds very much like rose budworm ( Pyrrhia umbra). The buds of roses, along with those of many other garden flowers, are chewed by two kinds of caterpillars. One is green with prominent, dark longitudinal spots and black tubercles; the other has whitish-orange markings on its back.

If there are not too many caterpillars around and you can make contact with them easily, a soap and water spray will knock them down. The ratio for the mix is 40 parts water to one part liquid soap. The essential thing is to make contact directly with the caterpillar. This is a continuing solution: You have to check your plants daily, and spray as required.

Rotenone spray is very effective on feeding caterpillars but, although it’s an “organic” pesticide, it is deadly poisonous. Follow the directions to the letter and be sure to wear personal protection when applying. This also holds true for the use of systemic insecticides such as Cygone and Sevin.

The benefit of these latter two products is that the poison is circulated throughout the plant and ingested by the feeding insects.

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The systemic applications also work for two other common pests that attack rose buds. One is the rose chafer ( Macrodactylus subspinosus), a fawn-coloured beetle with an elongated body about 1.5 centimetres long. It is a slow-moving beetle that feeds for about four weeks, then lays its eggs in the soil. These hatch within a couple of weeks and the grubs start feeding on the roots of lawn grasses. The grubs can cause heavy damage if the infestation is large in scale.

The rose curculio ( Rhynchites bicolor) is about three-quarters of a centimetre in length with a long weevil-like snout. As the Latin name suggests, it is two-coloured — reddish on the back and black underneath. Eating with its long snout, it leaves deep holes in rose buds, which then usually fail to open. Picking the hips or fruit off the infected plants also provides good control the following year since this destroys the larvae.

Ed Lawrence is chief gardener for Ottawa’s official residences and host of a CBC Radio phone-in show. Send your questions to

(Answer)

I suspect your unwelcome guest is the “rose slug” or larva of the sawfly. Here’s an image courtesy of the Missouri Botanical Garden.

Adult sawflies emerge in early spring and lay their eggs on the underside of host plant leaves. Larvae appear several weeks later, feed on soft leaf tissue for about a month, and then drop into the soil to pupate.

The Botanical Garden recommends early detection to get the pest under control. Begin looking for sawfly larvae in mid-spring Inspect both upper and lower surfaces of the leaves. Remove the infested leaves and destroy the larvae. A forceful spray of water out of a garden hose can also provide control by knocking off and killing many of the soft-bodied larvae. Be sure to aim the water at both upper and undersides of leaves. When the larvae are still very tiny, apply insecticidal soap as per the package direction. For larger larvae, removing and hand “squishing” is advised. Continue checking plants throughout the growing season.

Thanks for sending your photo. When you have several to send us, we find that sending them as separate posts works best. When we publish the question and answer, we will include as many photos as we think are needed.

Good luck

Holes in Your Rose Leaves? It Might be Rose Sawfly

The larvae are light green with a slimy appearance and tan heads and can be found on the underside of the leaves. While they look like caterpillars, they are actually the larvae of a stingless wasp-like insect. This is important to note because a common pesticide treatment for caterpillars, Bt (Bacillus thuringensis), is only effective on true caterpillars, the larvae of butterflies and moths. Bt will not control sawfly larvae.

If no larvae are visible on close inspection, they may have finished feeding, or have been controlled by other insects or birds that feed on the larvae. If no larvae are present and no new damage is seen, no control is needed as there is only one generation per year. You would want to watch for damage beginning in early June the following year so you can treat early.

If you’ve used Rose Rx Drench within 6 weeks the larvae should be controlled. The larvae can be knocked from the leaves with a strong water spray; once dislodged they will not be able to get back to the rose bush. Pesticides containing neem or spinosad are effective, as are insecticidal soaps and horticultural oils. Be sure to cover the bottom side of the leaves well when spraying as this is where the larvae generally stay. (During hot weather, be sure that you spray pesticides late in the day when it begins to cool, as spraying in full sun in high temperatures can cause leaf burn. Always read and follow the label!)

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Pest Problems: Rose Saw Fly

Posted 05.10.17

Here are pictures of a pest I have been battling for the last couple years on my knockout roses. Every summer they have been plagued with this insect, and my attempts at spraying had been unsuccessful. I think I finally have them figured out and have a few tips for control.

The tiny green worm you see is a rose saw fly. These larvae are out in early to mid spring and will feed on the leaves of your roses, before going back into the ground to lay new eggs. They can be organically controlled by spraying with a hard spray of water and knocking them off the plant. The larvae are a soft-bodied insect and the force of the water will easily kill them. They can be controlled with horticultural oils and other insecticides as well, however they must be sprayed directly on the insect, which resides on the underside of the leaves, making them hard to spray. Remember that all insecticides are non-selective, so there is a chance of killing other beneficial insects and natural predators, so use only as a last resort and spray in the early morning to avoid targeting the good insects.

I have been physically removing them and recently applied a neem oil. I want to see how this does, as it is not toxic to other insects that pass by unless they got sprayed at time of application. I carefully lifted each plant and sprayed underneath where I saw the saw fly larvae. *Neem oil does not quickly kill the pest, so do not expect them to die immediately. It uses hormones to affect their eating and reproductive habits, stunting them and keeping them from feeding and reproducing. Here is a good link for more information on how it works. http://www.discoverneem.com/neem-oil-insecticide.html

Rose slugs are infesting my 5 knockout roses. I saw one small yellowish…

Rose slugs are not true slugs. They are the larval stage of flying insects known as sawflies. They secrete a slimy substance over their body surface that makes them resemble small slugs. Rose sawflies are yellow-green in color and can grow to a ¾ inch maximum length.

Sawfly larvae feed on the surface of leaves of their respective host plant, removing the soft tissue leaving behind the papery, translucent surface and veins. Heavy defoliation gives plants a brown scorched appearance. In general, light to moderate infestations are cosmetic in nature and rarely harm the host plant. Heavier attacks, however, can weaken plants when leaf loss stresses them to the point of vulnerability to other insect and disease attacks.

Adult sawflies emerge in early spring and lay their eggs on the underside of host plant leaves. Larvae appear several weeks later, feed on soft leaf tissue for about a month, and then drop into the soil to pupate.

Integrated Pest Management Strategies

1. Check plants for signs of infestation. Early detection can often result in simple cultural control measures. Begin looking for sawfly larvae in mid-spring (rose sawflies) or early summer (pear sawflies). Inspect both upper and lower surfaces of the leaves. For light infestations, remove the infested leaves and destroy the larvae. A forceful spray of water out of a garden hose can also provide control by knocking off and killing many of the soft-bodied larvae. Be sure to aim the water at both upper and undersides of leaves. Continue checking plants throughout the growing season.

2. Support natural enemies of sawflies by responsible pesticide usage. Insects such as parasitic wasps, insectivorous birds, small mammals, predaceous beetles, as well as fungal and viral diseases all assist in keeping sawfly populations lower. Restraint in the use of pesticides allows beneficial species to assist your control efforts.

3. Use an Insecticide. Chemical controls are also available, but should only be used when necessary, not routinely as a preventive measure. Horticultural oil, insecticidal soaps, neem oil, bifenthrin, carbaryl, malathion, permethrin, cyfluthrin, imidacloprid, and acephate can all be used to control sawflies. Apply pesticides only when larvae are actually present, before infestations reach critical levels. Always be careful to read the label directions fully before applying any pesticide, and follow directions completely. Not effective: Bacillus thuringiensis (Bt), a commonly used biological insecticide that offers control of many caterpillars, is NOT effective against sawfly larvae.

Organic Strategies

Strategy 1 is a strictly organic approach. For an organic approach to Strategy 2, control other insects using strictly organic methods. For an organic approach to Strategy 3, consult the Organic Materials Review Institute (OMRI™) for appropriate insecticidal soap and Neem products.

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