June 20, 2025 • 8 mins
Roses are grown in many gardens for their large, showy, often fragrant flowers. If you grow roses, you may have noticed something eating the leaves of your plants, causing them to become unsightly. While various insects will feed on roses, one of the most commonly encountered pests is rose roseslugs. Check out this week’s Good Growing Podcast to learn more about these rose pests and how to manage them.
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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Ken Johnson (00:04):
Welcome to the good growing podcast. I am Ken
Johnson, horticulture educatorwith University of Illinois
Extension coming to you todayfrom Jacksonville, Illinois with
a gardenbite. And on this week'sgardenbite, we're gonna talk a
little bit about one of the morecommon pests we find on roses,
rose slugs. So roses are grownby many people in their gardens
for their large, showy, andusually fragrant flowers. And
(00:28):
while they may not be as popularas they used to be, they are
still quite popular gardenplants.
And if you've grow your ownroses or you've enjoyed roses,
looking at roses, you may havenoticed small holes in the
leaves or windowpane likefeeding damage on the leaves of
rose plants. And we often startseeing this sometime mid to late
spring and into the summer. Whenwe get later into the summer, a
(00:52):
lot of that damage is caused byJapanese beetles. But earlier in
the year, this is usually causedby rose slugs. So what exactly
are rose slugs?
We've got three differentspecies of rose slugs that can
be found here in Illinois. Sowe've got the European rose
slug, the curled rose sawfly,and the bristly rose slug. And
(01:14):
rose slugs are caterpillar likeinsects. But despite their
common name and theirappearance, they're not slugs
nor are they caterpillars, butthey are sawflies. And sawflies
are related to bees, ants, andwasps.
So these are gonna be in theorder Hymenoptera, and this will
become important when we getinto managing these pests. And
(01:34):
we often consider them pestsbecause they are feeding on
plants. Unlike bees, which arepollinating and and wasps,
they're feeding on other insectsand pollinating. Sawflies are
kind of the group of insects inthat Hymenoptera that we
generally consider pests becausethey will feed on plants and
cause damage. And they get theircommon name, sawflies, because
they have a saw like ovipositor,which is the egg laying
(01:57):
structure that they have, andthey're gonna use this
ovipositor to cut slits intostems or leaves of plants to lay
their eggs.
And like I mentioned, thesethese sawflies, they look like
caterpillars. And there's a fewways you can tell a caterpillar
and a sawfly apart. So forcaterpillars, their eyes are
very small and difficult to see.Whereas on sawflies, they have
(02:19):
relatively large eyes, and andthey can be seen pretty easily.
So if you think about in inchildren's books, stuff like
that, caterpillars are usuallydrawn with these big visible,
easily noticeable eyes.
What they're really drawing is asoft light. And another thing we
can look at, that's probably theeasiest way to tell them apart
is is to look at the eyes.Another way to tell them apart
(02:40):
is looking at the the pro legsof the of the insects. These pro
legs are fleshy structures onthe abdomen. They look and act
like legs, but they are notactually true legs.
So caterpillars are gonna havefive or fewer pairs of pro legs,
whereas sawflies are gonna havesix or more pair of pro legs. An
easy way to remember that is ifthey have enough to spell
(03:02):
sawfly, it's a sawfly. Back tothe ones that are causing damage
on our roses. So again, we'vegot three here in Illinois that
are typically causing problems.And all of these are going to be
introduced either from Europe orAsia.
European rose slug, these larvaeare light green, they're gonna
have orange heads, and it'llgrow to be about one half inch
(03:23):
long. Typically, they're feedingon the upper surface of leaves,
and they will leave behind theveins or the lower leaf surface.
So you can get some of thiswindow painting type damage from
them. And they're usuallyfeeding from May through June.
When they're done feeding,they're gonna leave the plants
and they will pupate in theground, and they're gonna stay
there until the followingspring.
(03:43):
So we only have one generationper year for the European rose
slug. The adults will thenemerge in the spring, and the
eggs are gonna be laid inpockets near the edges of the
leaves. Next, we've got curledrose sawflies. And again, these
are green, but they're gonnahave white spots and have yellow
heads with a dark stripe downthe middle. And they're gonna
(04:03):
grow to be about three quartersof an inch long as larvae when
they're full grown.
When they're small, again,they're gonna skeletonize
leaves. And as they grow larger,they can eventually eat entire
leaves except for maybe the mainmid vein of the leaf. For these,
in addition to their feedingdamage, when they pupate, they
will bore into the twigs of roseplants, particularly those that
have been pruned, and this cancause some further damage to the
(04:25):
plants. And the reason we callthem curled rose slugs is when
they will often curl up whenthey're when they're resting.
And for this particular species,we have two generations per
year.
The the final one and probablythe one we most commonly
encounter is gonna be thebristly roast slug. And these
are green and they're gonna havefine hair like spines on them.
And you have to get somewhatclose in order to be able to see
(04:47):
these. And they'll also grow tobe about half an inch long when
fully grown as larvae. Again,when they're small, they're
gonna typically feeding on theundersides of leaves and causing
that windowpane like damage.
So again, only the upper leafsurface is left behind there.
And then as the larvae getlarger, they can eat larger
holes and make it all the waythrough the leaf tissues there.
And if you get a lot of themfeeding those those feeding
(05:07):
holes, they can end up eating anentire leaf except for maybe the
large mid vein in the middlethere. When they are done
feeding, they're gonna spin acocoon and plant debris or
sometimes on the rose plantitself. And for these, there can
be six or more generations peryear.
And this means they are capableof causing, they can be capable
of causing extensive damage,especially towards the end of
(05:29):
the growing season, as thisfeeding damage keeps building up
and those populations,potentially grow higher and
higher. And the eggs for theseare gonna be laid in the midribs
of the rose leaves. So if youhave damage from rose slugs,
there's there's severaldifferent things we can do. And
again, remember, European andcurled rose slugs, we only have
one or two generations of these,so they're only present early in
(05:50):
the growing season. Because ofthis, management usually is not
necessary.
So this is where identificationis going to become important.
Again, however, because bristleroast slugs can be present
throughout the growing season,again, we have up to six
generations per year, maybemore, potentially on where
you're at in The States. Man wemay need to manage these if the
populations become too high. Soif you have small infestations,
(06:13):
we can remove these by hand,hand picking them, or we can use
a forceful spray of water can beused to knock often the small
larvae off of plants and makingwe need to make sure we're
getting both the upper and lowersides, undersides of the leaves
if we're gonna be doing this. Ifpopulations get too high,
insecticides can also be used tomanage the populations.
(06:34):
And then but remember, eventhough they look like
caterpillars, they're gonna berelated to bees, ants, and
wasps. So some of theinsecticides we use for to
manage caterpillars may not bevery effective, or something
like the bacillus thuringiensisgristachiae, BTK, that only
works on caterpillars. So youcan put that onto rose plants,
(06:55):
it will not affect sawflies. Soagain, identification is going
to be very important when we'retrying to manage these. So we're
using the proper insecticides inorder to manage these.
So some insecticides that we canuse to manage roast slugs,
something like horticulturaloil, insecticidal soaps,
acidophate bifenthrin, carbaryl,and cyclothrin are some of the
(07:16):
active ingredients you wouldwant to look at for managing
these. Again, if you do decideto use pesticides, make sure
we're reading and following allthe label directions, while
roses may have limited, if any,pollen, depending on the type of
flower you have. It's a fulldouble. But our more open
flowers will have nectar andpollen available to pollinators.
We wanna make sure we'reavoiding getting insecticides on
(07:38):
flowers, because anything thatwe are going to be applying to
kill rose slugs is more thanlikely going to kill pollinators
too.
So again, make sure you'rereading the label following any
restrictions that may be onthere for applying to flowering
plants because these areflowering. You may wanna remove
flowers or spray this in theevening when pollinators are
(08:00):
going to be less active. Butagain, there are other things
like hand picking or using a astrong spray of water to remove
these insects off of plantswithout the use of insecticides.
Well, that's all I've got foryou for this week's garden bite.
Hopefully, you have a littlebetter understanding of how we
can manage rose slugs in ourlandscape, or if you've got some
damage on your rose plants,hopefully, now you have an idea
(08:22):
of what may be causing it.
Good Growing podcast is aproduction of University of
Illinois Extension. Thank youfor doing what you do best and
that is listening or if you'reon YouTube watching. And as
always, keep on growing. Hi.
Welcome to the good growing podcast. I am Ken
Johnson, horticulture educatorwith University of Illinois
Extension coming to you todayfrom Jacksonville, Illinois with
a gardenbite. And on this week'sgardenbite, we're gonna talk a
little bit about one of the morecommon pests we find on roses,
rose slugs. So roses are grownby many people in their gardens
for their large, showy, andusually fragrant flowers. And
(00:28):
while they may not be as popularas they used to be, they are
still quite popular gardenplants.
And if you've grow your ownroses or you've enjoyed roses,
looking at roses, you may havenoticed small holes in the
leaves or windowpane likefeeding damage on the leaves of
rose plants. And we often startseeing this sometime mid to late
spring and into the summer. Whenwe get later into the summer, a
(00:52):
lot of that damage is caused byJapanese beetles. But earlier in
the year, this is usually causedby rose slugs. So what exactly
are rose slugs?
We've got three differentspecies of rose slugs that can
be found here in Illinois. Sowe've got the European rose
slug, the curled rose sawfly,and the bristly rose slug. And
(01:14):
rose slugs are caterpillar likeinsects. But despite their
common name and theirappearance, they're not slugs
nor are they caterpillars, butthey are sawflies. And sawflies
are related to bees, ants, andwasps.
So these are gonna be in theorder Hymenoptera, and this will
become important when we getinto managing these pests. And
(01:34):
we often consider them pestsbecause they are feeding on
plants. Unlike bees, which arepollinating and and wasps,
they're feeding on other insectsand pollinating. Sawflies are
kind of the group of insects inthat Hymenoptera that we
generally consider pests becausethey will feed on plants and
cause damage. And they get theircommon name, sawflies, because
they have a saw like ovipositor,which is the egg laying
(01:57):
structure that they have, andthey're gonna use this
ovipositor to cut slits intostems or leaves of plants to lay
their eggs.
And like I mentioned, thesethese sawflies, they look like
caterpillars. And there's a fewways you can tell a caterpillar
and a sawfly apart. So forcaterpillars, their eyes are
very small and difficult to see.Whereas on sawflies, they have
(02:19):
relatively large eyes, and andthey can be seen pretty easily.
So if you think about in inchildren's books, stuff like
that, caterpillars are usuallydrawn with these big visible,
easily noticeable eyes.
What they're really drawing is asoft light. And another thing we
can look at, that's probably theeasiest way to tell them apart
is is to look at the eyes.Another way to tell them apart
(02:40):
is looking at the the pro legsof the of the insects. These pro
legs are fleshy structures onthe abdomen. They look and act
like legs, but they are notactually true legs.
So caterpillars are gonna havefive or fewer pairs of pro legs,
whereas sawflies are gonna havesix or more pair of pro legs. An
easy way to remember that is ifthey have enough to spell
(03:02):
sawfly, it's a sawfly. Back tothe ones that are causing damage
on our roses. So again, we'vegot three here in Illinois that
are typically causing problems.And all of these are going to be
introduced either from Europe orAsia.
European rose slug, these larvaeare light green, they're gonna
have orange heads, and it'llgrow to be about one half inch
(03:23):
long. Typically, they're feedingon the upper surface of leaves,
and they will leave behind theveins or the lower leaf surface.
So you can get some of thiswindow painting type damage from
them. And they're usuallyfeeding from May through June.
When they're done feeding,they're gonna leave the plants
and they will pupate in theground, and they're gonna stay
there until the followingspring.
(03:43):
So we only have one generationper year for the European rose
slug. The adults will thenemerge in the spring, and the
eggs are gonna be laid inpockets near the edges of the
leaves. Next, we've got curledrose sawflies. And again, these
are green, but they're gonnahave white spots and have yellow
heads with a dark stripe downthe middle. And they're gonna
(04:03):
grow to be about three quartersof an inch long as larvae when
they're full grown.
When they're small, again,they're gonna skeletonize
leaves. And as they grow larger,they can eventually eat entire
leaves except for maybe the mainmid vein of the leaf. For these,
in addition to their feedingdamage, when they pupate, they
will bore into the twigs of roseplants, particularly those that
have been pruned, and this cancause some further damage to the
(04:25):
plants. And the reason we callthem curled rose slugs is when
they will often curl up whenthey're when they're resting.
And for this particular species,we have two generations per
year.
The the final one and probablythe one we most commonly
encounter is gonna be thebristly roast slug. And these
are green and they're gonna havefine hair like spines on them.
And you have to get somewhatclose in order to be able to see
(04:47):
these. And they'll also grow tobe about half an inch long when
fully grown as larvae. Again,when they're small, they're
gonna typically feeding on theundersides of leaves and causing
that windowpane like damage.
So again, only the upper leafsurface is left behind there.
And then as the larvae getlarger, they can eat larger
holes and make it all the waythrough the leaf tissues there.
And if you get a lot of themfeeding those those feeding
(05:07):
holes, they can end up eating anentire leaf except for maybe the
large mid vein in the middlethere. When they are done
feeding, they're gonna spin acocoon and plant debris or
sometimes on the rose plantitself. And for these, there can
be six or more generations peryear.
And this means they are capableof causing, they can be capable
of causing extensive damage,especially towards the end of
(05:29):
the growing season, as thisfeeding damage keeps building up
and those populations,potentially grow higher and
higher. And the eggs for theseare gonna be laid in the midribs
of the rose leaves. So if youhave damage from rose slugs,
there's there's severaldifferent things we can do. And
again, remember, European andcurled rose slugs, we only have
one or two generations of these,so they're only present early in
(05:50):
the growing season. Because ofthis, management usually is not
necessary.
So this is where identificationis going to become important.
Again, however, because bristleroast slugs can be present
throughout the growing season,again, we have up to six
generations per year, maybemore, potentially on where
you're at in The States. Man wemay need to manage these if the
populations become too high. Soif you have small infestations,
(06:13):
we can remove these by hand,hand picking them, or we can use
a forceful spray of water can beused to knock often the small
larvae off of plants and makingwe need to make sure we're
getting both the upper and lowersides, undersides of the leaves
if we're gonna be doing this. Ifpopulations get too high,
insecticides can also be used tomanage the populations.
(06:34):
And then but remember, eventhough they look like
caterpillars, they're gonna berelated to bees, ants, and
wasps. So some of theinsecticides we use for to
manage caterpillars may not bevery effective, or something
like the bacillus thuringiensisgristachiae, BTK, that only
works on caterpillars. So youcan put that onto rose plants,
(06:55):
it will not affect sawflies. Soagain, identification is going
to be very important when we'retrying to manage these. So we're
using the proper insecticides inorder to manage these.
So some insecticides that we canuse to manage roast slugs,
something like horticulturaloil, insecticidal soaps,
acidophate bifenthrin, carbaryl,and cyclothrin are some of the
(07:16):
active ingredients you wouldwant to look at for managing
these. Again, if you do decideto use pesticides, make sure
we're reading and following allthe label directions, while
roses may have limited, if any,pollen, depending on the type of
flower you have. It's a fulldouble. But our more open
flowers will have nectar andpollen available to pollinators.
We wanna make sure we'reavoiding getting insecticides on
(07:38):
flowers, because anything thatwe are going to be applying to
kill rose slugs is more thanlikely going to kill pollinators
too.
So again, make sure you'rereading the label following any
restrictions that may be onthere for applying to flowering
plants because these areflowering. You may wanna remove
flowers or spray this in theevening when pollinators are
(08:00):
going to be less active. Butagain, there are other things
like hand picking or using a astrong spray of water to remove
these insects off of plantswithout the use of insecticides.
Well, that's all I've got foryou for this week's garden bite.
Hopefully, you have a littlebetter understanding of how we
can manage rose slugs in ourlandscape, or if you've got some
damage on your rose plants,hopefully, now you have an idea
(08:22):
of what may be causing it.
Good Growing podcast is aproduction of University of
Illinois Extension. Thank youfor doing what you do best and
that is listening or if you'reon YouTube watching. And as
always, keep on growing. Hi.
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