Knockout Rose Insect Damage

Cindyloo123June 10, 2012

Hello rose growers! I live on the decorating forum but had to stop in here for some help!

After four years of telling everyone I know how carefree the knockouts are, no bugs,no diseases, etc., suddenly this year something is destroying my roses. It seems like in one week's time my largest shrubs went from pristine to leaves that are full of holes.

I have eight knockouts and they are scattered around in various flower beds. They are all showing some damage, but it varies according to which bed they are in.

When I see holes in leaves I always think slugs. I treated for them last month and today I treated for them again. Then I sprayed all of the shrubs with an all purpose insecticide. When I was spraying I noticed all of the shrubs had insect webs in them.

Any advice from anyone? Is it definitely insects or could it be a disease? None of my other plants are showing any damage at all! Thanks for any help.

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I just did some research and it seems most gardeners do not think it wise to use insecticides.

Maybe in the morning I could hose my knockouts off? Or is it too late?

This is a fine mess I've caused, lol, and I LOVE these roses:

    Bookmark   June 10, 2012 at 12:31AM
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JessicaBe(5-6 Central Ohio)

This is what mine looked like and I HAD to spray mine, what I have a problem with is sawfly larvae (rose slugs) I was squishing them but my KO is so big I had to spray. I had a better/worse photo of the damage but I can't find it. I was worried about killing the good bugs like butterflys and ect so the greenhouse told me to spray at dusk when they aren't active.

    Bookmark   June 10, 2012 at 12:50AM
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cecily(7 VA)

Spraying an insecticide one time to stop an obvious infestation is okay! Repeated use of an insecticide as a preventative measure tends to lead to a spider mite infestation (and those guys are tough to kill). Hosing your roses regularly with a strong stream of water is a great way to reduce insect damage ( and removes fungal spores) so hose away. Since Knock-out is a fast grower, you will always have lots of succulent new foliage that will attract lord knows what sort of pests so you do need to keep an eye on them and treat as necessary. Most insects can be squished but if an infestation gets out of hand, don't feel guilty about spraying.

    Bookmark   June 10, 2012 at 8:37AM
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flaurabunda(6a, Central IL)

A couple of questions, to help diagnose what's happening so that you'll get the most accurate feedback:

Where are you? (Zone, general location)
Where are the webs? Are they near the base of the plant, or are they up higher and around the tips of the canes?
What do the holes look like? Are they small and irregular, with more than 2 per leaf, or are they large, nearly perfectly circular, and infrequent?

    Bookmark   June 10, 2012 at 9:13AM
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karl_bapst_rosenut(5a, NW Indiana)

Aside from the few holes in the leaves, is the damage that bad you had to spray an insecticide? The damage I see is not so bad as to cause any permanent damage or death to the plant. Not having a perfect leaf phobia, I've found walking quickly past the bush makes it difficult to see the damage. Once the bugs mature, they disappear or if you don't spray and allow Mom Nature to take care of things, predatory insects and birds will eat them.
I don't really think Nature intended plants to be perfect. She provided them as food for the insects. There are enough plants so they can survive and still supply the needed food for the bugs.
Keep in mind, Caterpillars, which eat foliage turn into butterflies. I gladly sacrifice a few leaves for the later beauty of a butterfly.
I haven't sprayed in over 10 years. I probably have less insect damage in my 400 rose garden than you have on the one plant pictured.
Bugs got to eat too!

    Bookmark   June 10, 2012 at 11:57AM
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Thank you for the picture Jessica, you saved me the trouble to taking pictures of my damage. It is the same. The only difference is, your pictures shows what the least damaged of my shrubs look like. On the worst of them, about 1/4 of the leaves are so eaten up they look like lace. Oh, and those white spots on your leaves are identical to the spots on many of my leaves. As I understand it, those spots will become new holes?

I just went outside and tried to find bugs on the undersides of the leaves. I found a few...small green worms.

Flaurabunda, I'm so sorry for not mentioning my zone. I am in Northern MD, only 8 miles for Delaware. Zone 6-7? The webs are across the top sections of the canes. I will remove them today! The holes are not perfect circles by any means and there are tons of them. Just like Jessica's picture only the damage ranges from what she had, to "lace" leaves, depending on the location of the shrub.

Jessica, I am optimistic AND lazy. I saw the damage starting about 7-10 days ago. I let it go until it was too horrible to ignore. The worst damage is on my two original shrubs, which are my pride and joy as they flank my most heavily used entrance. I have enjoyed four full seasons of perfection from those shrubs. I do feed/treat them with that rose food/insecticide combo granule several times a year, beginning in March. Maybe in past years that is what prevented this problem. This year has been exceptionally dry so I would think the insecticide would have lasted LONGER, but maybe not. sigh

Thank you all for your input. In the interest of helping others as I have been helped, I will take several photos of the damage today and get it uploaded to this thread.

    Bookmark   June 10, 2012 at 12:20PM
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Ooops Cicily, thanks for the help. Spider Mites are the bane of my existence. I can't seem to prevent them and I finally stopped putting in the type of plants they like.

My neighbor is an obsessive gardener. Everything in his yard is cared for to perfection. But even he can't keep the kinds of evergreens that spider mites like. While this makes me feel better, lol, it reinforces my belief that I must never again attempt to install those types of evergreens!

    Bookmark   June 10, 2012 at 12:45PM
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dublinbay z6 (KS)

Cindyloo, you said "I do feed/treat them with that rose food/insecticide combo granule several times a year."

You will find that most of the posters on this forum avoid those "rose food/insecticide combo granules" like the plague. That is exactly the kind of product that kills off the good bugs (that eat the bad bugs) along with the bad bugs. In other words, you are killing off the predators that would keep some of your bad bugs under control. Those combo products also often lead to later spider mite infestations. Get rid of the combo stuff and just use straight rose food. Your roses will thank you--and so will a lot of buggy critters that are there to help your roses, not destroy your roses.

If you run into a problem with your roses, check here first. Posters can give lots of advice on non-insecticidal ways to get rid of bad bugs without harming the good bugs.


    Bookmark   June 10, 2012 at 1:07PM
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jerijen(Zone 10)

Also, Cindyloo -- if your infestation of sawfly larvae is that advanced, they're probably about to turn into sawflies and leave.

At this point, adding MORE pesticides to your garden (in addition to the combo stuff) isn't going to do much for the rose slugs (sawfly larvae) but it sure will help to increase your spider mite problems.

Squishing the remaining rose slugs, and hosing off your plants will do you a lot more good OVER THE LONG HAUL.

OH, and the combo stuff (in addition to its other flaws) isn't even very efficient! You notice, it din't discourage the rose slugs, and it's a poor choice for aphids, as well. If you HAVE to use a pesticide, use one selected for what's causing the problem, and use it ONLY when you need it.

Among the other virtues of this approach is the fact that you will save money.


    Bookmark   June 10, 2012 at 1:33PM
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reg_pnw7(WA 7, sunset 4)

Zone/area are critical info. My first thought on reading the original post was, is she in an area with Japanese beetles? and yes you are. But, the photo posted lower down is definitely sawfly damage, so if that's what your damage looks like, then it's probably sawflies.

Insect webbing? few insects make webbing. Spiders make webbing. Webbing on the tops of the plants is probably spiders. Spiders are beneficial. Spider mite webbing is so fine and tiny as to be almost invisible, and on the undersides of the lower leaves, only slowly making its way up the plant to the top. Any insecticide usage will encourage spider mites by killing off beneficial insects that eat mites.

In my area you can't just ignore sawflies as there are multiple generations a year. In other areas there are different species. If you catch it early you can search and squish. Otherwise, they're one of the very few insects I will use insecticides for.

As a general rule of thumb, do not use insecticides until you know what insect you have. Don't spray first and then ask what it is! I had a gardening client that obsessively squished every single black and orange bug she could find on her roses, and only later brought one in for me to identify - she'd been squishing lady bug larvae. And sometimes insecticides will just make things worse.

    Bookmark   June 10, 2012 at 2:11PM
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JessicaBe(5-6 Central Ohio)

Karl the picture is not at all bad that is the usual for me right now with my roses but my leaves were gone on some canes, it was getting eaten alive. I don't like to spray I just squish. I don't like perfect plants it makes them to fake. I waited for the good bugs to come in but they never showed so I just sprayed that once.

    Bookmark   June 10, 2012 at 3:03PM
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jerijen(Zone 10)

Jess -- BUT if you were using a combination including a pesticide, you were systematically ELIMINATING the "good bugs."

Tell you something else, too ... When you've been using a product like that -- or spraying regularly with non-specific pesticides -- you can't just turn it off and have predators show up the next day. When we quit spraying (after seeing one of our dogs seizure everytime the chemicals came out) it took a good YEAR before the garden balanced out. We just told people, "Nooooooooo . . . this is not a good time to visit our garden."

But nature DOES balance things out, eventually. Birds start to show up and eat rose slugs and aphids. Hummingbirds LOVE aphids and whitefly . . . It does balance out. Just takes time and patience to let nature work. She's a grand ol' gal, and she'll do it, given the chance.


    Bookmark   June 10, 2012 at 4:06PM
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JessicaBe(5-6 Central Ohio)

I am trying to attract hummingbirds so thats good they like aphids :)

    Bookmark   June 10, 2012 at 6:51PM
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Thank you again to all who contributed their wisdom. I have been schooled! No more spraying first and asking questions later. No more removing spider webs because I thought they were the next batch of harmful insects waiting to hatch.

I think my problem involved both sawflys and beetles. The leaves that look like lace, must be the beetle damage. I didn't know the beetles were here yet till I was hosing off my roses and I saw one fly by me!

Now, should I or should I not use some Sevin to ward off the beetles? This is the first time since putting in my first Knockouts that I've seen beetle damage on them!

    Bookmark   June 12, 2012 at 3:14AM
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cecily(7 VA)

Hi Cindyloo, how large is your yard? If you have a couple of acres, the Japanese beetle bags work wonders. If you have a small suburban lot, the bags will attract hordes of beetles that will devour your roses and do vulgar things in the process and many of them won't go into the bag.

The JB pressure varies widely from one area to another. I picked ten off our apple tree yesterday and that's a lot for me. There are forum members who post photos of roses absolutely encrusted with beetles. I just use a cup of soapy water to kill mine since I don't really have all that many. If others with huge infestations choose to use other means, I won't judge them. The sevin doesn't really work all that well because the beetles are such good flyers - reinforcements keep coming (and sevin kills bees). Cutting off the rosebuds during beetle season helps moderately. Perhaps others have better solutions for you. Good luck1

    Bookmark   June 12, 2012 at 7:45AM
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Hi Cecily, I have an acre and there is a lot of undeveloped land around me.

I've tried the beetle bags but I am certain they were a gift to my neighbors because I believe all the beetles came to my house. In fact, in recent years my next door neighbor has been putting out the bags and I swear, that is why I have had so little trouble with beetles myself.

For a few years I was growing Hybiscus as an annual. But those bushes drew the beetles better than the bags did and by July the leaves looked like lace. I stopped growing them because of it.

Since getting rid of the Hybiscus, the only beetle damage I've endured was on my Rose of Sharon. I have a huge bush in a fairly concealed spot, I don't like the flowers anyway, and it has kept the beetles busy for the past few years. The Rose of Sharon and my neighbor's bags, lol.

I've been relieved that my Knockouts haven't had beetle damage. And just as I was certain they were the ultimate flowering shrubs, I see slug and beetle damage!

Oh well. If it were all easy, everyone would have yards full of flowers wouldn't they? Thanks for the comment on the Sevin. This business about protecting good bugs is new to me, but I'm going to do my best to go with it in the future.

    Bookmark   June 12, 2012 at 10:38AM
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Sorry to bring back an old topic but I am new to the rose/gardening life.

The pic JessicaBe posted is how mine like but the leaves are much worse all over the plant. Just planted my KO's the first of spring. The one bush is so bad it hasn't had any new growth or blooms in the past two weeks.

Now it is spreading to other rose bushes in the yard.

I would prefer not to use insecticides but with it spreading to other bushes what would the best advise be?

    Bookmark   August 10, 2013 at 12:57PM
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michaelg(7a NC Mts)

As you have read above, it is rose slugs (which are not slugs but sawfly larvae). You can wipe them off the backs of the leaflets or you can spray with an insecticide containing spinosad, reaching the underside of the leaves. Roses that do not show any damage do not need to be sprayed. The sawflies prefer certain varieties. If you spray in the evening, spinosad is not hard on beneficial insects, and it is relatively safe to handle. You could also use a "house and garden" aerosol containing pyrethrins, being careful to follow the instructions.

    Bookmark   August 10, 2013 at 1:14PM
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catsrose(VA 6)

I use Milky Spore for the Japanese Beetles. It slow (and expensive), but I add to it each year. I does not completely eliminate them because they do fly in from the neighborhood, but it does keep them under control in my yard.

None of these bugs will kill your roses. Unsightly, yes. But the bugs go away and roses almost always recover in time for their fall flush. As Jeri pointed out, Mother Nature knows what she's doing.

    Bookmark   August 10, 2013 at 4:29PM
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