Hole-y Knockout Rose Bush

[micvog]

A "Double Knock-Out Rose" was installed in my landscaping last Fall and after a few weeks there were a number of holes in the leaves. I sprayed some EcoSmart insecticidal soap (different oils such as rosemary, peppermint, and thyme). It seemed to help and then winter came.

The holes are back. Is this insect damage? The neighboring plants, "Magic Carpet Spirea", don't seem affected which has me wondering if it is some kind of rose-specific disease.



Thanks! A few years ago I wasn't at all interested in landscaping then the "grass bug" got me. Now the "plant bug" is starting to take root.

[andy10917]

Pinging Bernstem (our resident Rose guy) to the thread.

[bernstem]

Looks like insect damage. Maybe rose slugs. You can look on the underside of leaves for small green caterpiller like slugs. Generally, the problems are cosmetic. It is unusual to have damage severe enough to affect the overall plant. They can be treated by removing and crushing them or with insecticides (which I think is overkill). They are best found in the early morning or evening when it is cooler. If you ignore them, predator insects will come in and eat them solving the problem. I ignore them and let nature take care of the problem. I have one bush that looks a lot like that right now.

[micvog]

Thanks Andy and Bernstem! I will check for the slugs tomorrow AM.

[Overfloater]

I have 30 or so knockouts on my property and have always had the same damage. Must be slugs even though I never see them.

I do always see tons of other insects, quite a few mantises.

Knockouts are tough plants. They don't seem to miss a beat because of that damage.

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[HomerGuy]

I've got a few knockout roses in my backyard. They always look this exact same way, but it never seems to cause any problems.

This spring I cut them back to the ground. I have always heavily trimmed them in the early spring, but this year I went full boat and took them all the way down. I was really nervous and the wife thought I killed them. But they came back better than ever this year!

[bassadict69]

Spider Mites! We got them bad last year. Best I could tell from researching it, it to spray down all the bushes from all angles with a fairly strong stream of water to knock them off the leaves. Once we began doing this last summer, they recovered fairly quickly.

This year, every couple days I am hosing them down good HOPING to prevent them!

[jfoege]

This looks, to me, like damage from either leaf hoppers or spider mites. Rose slugs leave a more characteristic "trail" on the top of the leaf as they chew the layers underneath, but they don't tend to skeletonize the leaves in my experience with them.

Rose slugs are actually sawfly larvae, and as people have mentioned above, it's quite easy to go out there and squish them as you find them on the backside of your leaves - unless of course you have 30 bushes and then it's just too much work. Rose slugs, again, as people mentioned, in my experience, don't cause enough damage to severely damage the bush, but they do mar the shiny green perfect foliage look! It's quite unsightly if you are trying to grow the perfect rosebush!

Spider mites can skeletonize leaves very quickly and leaf-hoppers also chew holes, as I've noticed on my roses.

Since I've started a preventative spraying program of Neem Oil every week, I've been able to get black spot, powdery mildew, rose slugs, aphids, leaf-hoppers, and spider mites under control. Neem is really a great product for roses. It handles most all of their fussy little issues, but it does take weekly spraying over a course of time to really start to "work".

I mix 2 tsp of 100% Pure Neem Oil (Dyna-gro on Amazon, they call it a leaf polish, but that's just for legal reasons imo) and 2 tsp of liquid castille soap (you could use Ivory) in a 32 fl. oz. sprayer bottle and shake vigorously. I then walk around and spray the foliage of my roses, spraying from the bottom up, as most pests live on the bottom of the leaves. Then I douse the foliage on the top side of the leaves as well. I always do this in the evening around 6 or 7pm to make sure the beneficial insects and pollinators don't get a dose of soap or Neem, which will harm them, and I make sure rain isnt in the forecast for the foreseeable future.

It gives your foliage a wonderful gloss, controls fungal diseases, and controls common rose pests! It's the all-in-one wonder (for me at least). I don't use the stuff from the store labeled as "Clarified extract of Neem Oil". It does not contain the azadirachtin that 100% cold-pressed Neem contains in the same significant quantities.

For 30 bushes or more, I'd be mixing up amounts in my gallon sprayer and spraying weekly. I've had much success with the above methods.

[bernstem]

I have seen rose slugs skeletonize leaves. You can look for small brown spots on the front of the leaves to diagnose rose slugs. Spider mite and leaf hopper damage looks different and is more diffuse. The best way to tell them all apart is to look for the offending insect on the underside of the leaf. This site: http://buggyrose.tripod.com/irosepests.htm has lots of pictures.

Neem oil works pretty well, but I just don't have the patience to spray all my roses weekly. The damage is generally self limiting so I let natural predators come in and clean up. It does leave some of the bushes pretty sketchy looking in the middle of summer, though.