Sawfly Larvae Help!!!

knash6(z7 GA)April 26, 2012

So, my old neighbors came over last night telling me about how their gorgeous roses, taller than me, pretty much defoliated within a couple of days. They said they were just sticks now and what to do? I drove by and could not believe my eyes. Less than a week ago they were so thick and lush, now like they said they are just sticks now. Research points to the sawfly larvae, so I decided to check my roses. Could not find a thing, but noticed a tons of damaged leaves as well.

Sometimes it takes young eyes I guess, but tonight Maddi found the little suckers...tiny tiny green wormy things on the underside of the leaves. I have never had this happen before in the 12 years or so that I have been growing roses. I am at a loss...what do I do??? Please give me a plan of attack before they are reduced to sticks as well.


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knash6(z7 GA)

    Bookmark   April 26, 2012 at 8:36PM
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Saw Fly are miserable creatures! I'm sorry! The three least toxic alternatives are Insecticidal Soap, Ultra Fine Horticultural Oil and Serenade organic bacterial. Each has its pluses and minuses. Insecticidal Soap is potassium salts of fatty acids. It is made from lard, animal fat. It dries out the exoskeleton of the insects so they can't molt and strangle in their skin. It is highly caustic to eye tissue and skin as it dries them out, too. It also is an oil, which can burn the foliage with intense sun, high heat and/or water stress.

Horticultural Oil is also an oil. It suffocates the insects, "cures" mildew and can prevent other fungal attacks. It can also fry the foliage off a rose in an afternoon under the same conditions the Insecticidal Soap can. You may find highly refined, Paraffinic Oil which is water soluble, or even a Canola Oil spray. Both are oils. Both will seal the stomata, the pores on the undersides of the leaves and prevent water transpiration leading to foliage burn with sufficient heat/bright, direct sun/water stress.

Serenade is an organic bacterial, IF you buy the Greenlight brand. If you buy the Monterrey Brand it is the same bacteria, but it isn't manufactured in accordance with organic procedures. It kills insects through nervous exhaustion. It will not burn foliage under any circumstances, though many here are about to scream that it is toxic to bees. Everything is toxic to something. Both the Insecticidal soap and horticultural oil are phytotoxic, they can and WILL burn foliage when sun, heat, water stress are sufficient. NO, you can't spray after dark or on a cool day nor can you wash it off to prevent burning. Oils do not "wash off" with water. There will be residue left and it CAN burn. In my climate, I have experienced foliage burn up to six weeks after application of both Insecticidal Soap and Horticultural Oils. I read and follow directions religiously and use all chemicals VERY sparingly (read almost never).

The bacterial can be toxic to bees, particularly when wet. These three are the least toxic to you, your pets, neighbors and any other wild life which may wander in. ALL THREE are toxic to fish and other water life, so you have to make sure the over spray doesn't drift into ponds and that any rinse-out doesn't affect water ways. When used properly, all three will help knock down Saw Flies and many other insects. All three require being sprayed on the undersides of the foliage for greatest effectiveness as that is where the little beggars mostly are. It's your choice which is the least offensive to you and which is the most appropriate for your heat, sun, garden, etc. Kim

    Bookmark   April 26, 2012 at 10:01PM
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Sorry, strike that! Serenade is an organic fungicide. Spinosad is the organic, bacterial insecticide. That'll show me to multi task! Substitute Spinosad for Serenade above and it's correct. Sorry about that! Kim

    Bookmark   April 26, 2012 at 10:04PM
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knash6(z7 GA)

Thank you Kim for your reply. :) I think the very mild winter here has the bug population going crazy. I have never seen such damage (not mine yet), but my friend's. Not even in my worst Japanese Beatle years. I really hate to spray any pesticide at all. I just don't have any experience with this problem. How long do they tend to stay around? What is the life cycle of these guys? The JB phase comes and goes pretty quick and I can deal with this. If these stay for a lengthy amount of time I may need to reconsider. I have tons of bees, wasps (I read are beneficial), etc. I don't want to kill everything. :(

    Bookmark   April 26, 2012 at 10:21PM
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You're welcome Kristi. I'm afraid pretty much anything you spray is going to negatively affect beneficials to a certain degree. The Saw Flies can hang around as long as weather conditions suit them. In milder areas inland here, they hit when it's like greenhouse conditions, but go away as soon as it heats/dries up. Along the coast, in many places, they are nearly year round. As soon as your weather heats up, dries out or gets cold, they will disappear. Good luck! Kim

    Bookmark   April 26, 2012 at 11:26PM
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My roses were attacked by sawfly larvae the year before last. At the time I was new to roses and only had a few 'Knockout' bushes, so I'm not sure what effect these pests would have on a larger or more varied collection of roses, but I'll share my experience for what it's worth.

I am a strictly non-toxic gardener and figured I would let nature take its course. It did, and the roses looked very ratty for about half the summer before they leafed out again once the sawfly "phase" was over. Since that year, I have noticed no more sawfly larvae or damage...perhaps there is a natural predator taking care of them for me now that I have so many more roses. I don't know about sawfly life cycles, but I agree that would be interesting to find out about should they crop up again. I do know that you can just about rule out simply picking them off the plant--as you've noted, they're too daggone hard to see! :)

    Bookmark   April 26, 2012 at 11:32PM
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roseblush1(8a/Sunset 7)


I was wondering that since I have been spraying my roses every day to help slow down the transpiration rate due to the heat in my garden, I have found that I almost have no sawfly problem at all. I know I had a problem when I first started gardening up here.

Do you think that spraying/washing the roses is one way to manage the sawflies ?


    Bookmark   April 27, 2012 at 12:24AM
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Water can help knock down many insects, but I'd imagine your lack of saw fly is more due to the heat than your washing the roses. They like greenhouse conditions...mild, damp, humid, just like we get at the beach here; like many areas get in spring to early summer with humidity. When it gets hot and dry, there are no sawflies, just as there are no white flies. Make it milder, more humid, the kind of conditions where aphids flourish, and you get sawflies. Kim

    Bookmark   April 27, 2012 at 12:58AM
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flaurabunda(6a, Central IL)

I've had problems with these little buggars ever since I started growing roses. They cycle, too, from what I understand. So you may notice them, then they cycle through to adulthood, lay eggs or whatever, and more appear later.

Only once or twice have I used pesticide to try to rid our garden of them, and it didn't work very well. The next cycle came back worse than ever because I killed everything else that had been eating the larvae.

The only luck I've had is to smash the ones I see, but I usually see only the damage & not the larvae. I've never seen a plant defoliated from them, though. The most damage I've seen are a few skeletonized leaves and multiple leaves with holes.

    Bookmark   April 27, 2012 at 9:40AM
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roseblush1(8a/Sunset 7)

Thanks, Kim.

I wasn't sure.


    Bookmark   April 27, 2012 at 9:40AM
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knash6(z7 GA)

THanks all...Well, being here in Atlanta and the heat going up to the the mid 80s this weekend, maybe they will decide it's too hot for I am hoping for the best here. My friends roses were just such a sad and shocking thing. I have never seen damage that bad and that fast. When I got home from work today, I have been looking for them, but I guess I am blind. Maddi has those young eyes! lol I cannot find them at all, however, I am encouraged by all the wasps in the garden patrolling the roses. I am very glad I didn't decide to do them in as planned. (allergic) We will co-exist now that I know they are good to have.


    Bookmark   April 27, 2012 at 4:48PM
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Kristi, it could well be your garden is drier and hotter than your friend's. As with aphids, you can frequently see pockets of infestation, where much of the other area seems unaffected. It all depends upon how sheltered the spot is. Anything which increases the humidity, protects from intense sun, restricts air circulation so it increases the "green house effect", making the area milder, more "nursery like" which is to their liking, can cause a proliferation of them in smaller (or larger) areas. I won't generally have issues with aphids here on this hill because there is nearly constant, at least, breeze and often wind. Not far away, in more sheltered places, on the same day, same weather, nearly same elevation, there will be insect and disease issues I simply don't have because I don't have as much of the "green house" situation. I will experience a bit of it in the front, walled garden where there are only a few hours of direct sun, the walls and dense foliage increase the humidity and mitigate the intensity of the heat, causing it to feel more humid and milder, but the rest of the area is windy, hotter and drier so they don't have the bug and disease issues the walled front area is guaranteed to. You might have just a few pockets of problems remaining after the heat hits. If your friends have more shade, more evaporation from dense foliage, less air flow, they may have repeated cycles of them where you may only have one or two. Nature doesn't live by calendars, clocks or geographic location (usually), but by conditions. If the micro climate supports the "problem" and what's necessary to enable it is provided, it will occur.

Usually the west San Fernando Valley here has NO Giant White Fly because it is HOT and DRY, but a few summers ago, we had a very humid period and there were Giant White Flies all over the hibiscus where historically there never have been. In the Santa Clarita Valley, where I used to live, saw fly and giant white fly have never been known as it is always too hot and too dry with winters far too cold to support them. But, one summer, in a walled rear garden where there was frequent irrigation, no wind, higher humidity and filtered sun due to the trees, there were saw flies and giant white flies. None elsewhere in the garden and none on the neigbors' plants that I could see evidence of. It's like fungal issues, yours could be clean and next doors' terrible, without any preventative measures taken. It all depends upon conditions which support the outbreak. Only time and observation will tell for sure. Another 'wait and see' situation. Kim

    Bookmark   April 27, 2012 at 5:11PM
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jerijen(Zone 10)

We get them some years -- usually after everyone else. It gives me great satisfaction to squish the little beggars. They actually pop nicely. The good news is, they can't move fast, so, you'll usually find em, right close to the damaged areas, and you can git 'em.


    Bookmark   April 27, 2012 at 7:57PM
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dublinbay z6 (KS)

Go out early in the morning and stare at leaves in the damaged areas--look underneath them and along the edges of the leaves. Once you learn how to see the little green "worms," you will find you can get very adept at it, even spotting them as you are approaching the bushes.

If you aren't up to squishing, just pick them off the leaves and toss them out in the middle of your grassy lawn. Chances are highly unlikely they will find their way back to the rose. After you do that for a week or two (in the morning, remember), the beneficials will show up and finish off the job for you, very quickly in fact. I can't remember what the beneficial is for sawfly larvae, but it takes about 10 days for them to show up. Then, no more problem since the weather will probably have changed by that time anyway.

That's how I do it, anyway.


    Bookmark   April 27, 2012 at 8:29PM
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Sorry gang. I'm not a purest. I keep a bottle of Bayer Complete insect "bomb" handy for unwelcome guest. Only use it when I need to. Maybe 2 or 3 times in the spring. Very rarely after that. It works and that is what I want. Mix it according to directions. Spray at dusk. No bugs.

    Bookmark   April 27, 2012 at 9:17PM
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jim1961 Zone 6a Central Pa.

Our Sawfly Larvae is here from May until

    Bookmark   April 27, 2012 at 11:10PM
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rosetom(7 Atl)

ken-n-ga.mts - what you said. :-)

There is nothing wrong with the occasional, judicious use of insecticide ... especially here in Georgia. There's just no way around it sometimes.

    Bookmark   April 28, 2012 at 3:18PM
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michaelg(7a NC Mts)

If you want to use chemical insecticide, spinosad (recommended by Kim) is by far the best choice. It doesn't cause mite flareups and is relatively easy on beneficials. Fertilome Bagworm. . .Spray, Green Light Bulls Eye, and Monterrey Insect Spray are some brand names. You won't find these at the box store.

Paper wasps usually control them in my garden. I watch out for the characteristic rectangular holes and skeletonizing. When I see that, I wipe under the leaf with my thumb. Typically they occur in patches as the winged adult female lays eggs on several leaves near each other.

Rose slugs occur just about everywhere in the lower 48 (maybe not FL or AZ), but I've never seen plants defoliated as the OP witnessed. So, generally, no need to panic; severe damage would be unusual. They do have natural enemies.

    Bookmark   April 28, 2012 at 4:17PM
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