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Hello, All. My Knockout roses are reviving thanks to drier weather but, sadly, I now notice borers all along my forsythia hedge. HELP! I know it is late in the season but is there anything I can do to save them?


By Lisann

Maryland, United States Us

I have read about systemic 'Merit' insecticide. It is Imidacloprid and I am wondering if I should put it down now and then cut the forsythia to the ground and hope for the best.
Any ideas would be greatly appreciated.

Thanks! Lisann



I see you are in the USA where conditions may be different but generally forsythia is extremely resistant to pests and diseases. I would cut down the forsythia in any case as any flowers next spring will be on new growth. You may lose most of the display for next spring but you should get rid of most of the pest this way. Forsythia is very resilient so should shoot again from the base without your pest problems.
These are the pests mentioned in Wikipedia:
Crown Gall caused by Agrobacterium tumeifasciens
Leaf Spots caused by several species of fungi including Alternaria and Phyllosticta spp.
Dieback caused by Sclerotinia sclerotiorum
Root Knot
Meloidgyne hapla: Northern Root Knot Nematode
White Peach Scale: Pseudaulacapsis pentagona
Four-Lined Plant Bug: Poecilocapsus lineatus
Twobanded Japanese Weevil: Callirhopalus bifasciatus
Redheaded Flea Beetle: Systena frontalis
Twobanded Japanese Weevil: Callirhopalus bifasciatus (on roots)
Not sure what you mean by 'borers'.

14 Jul, 2009


Hi, Bertiefox:

Thanks for your reply. Would you recommend cutting them to the ground now? We are coming up on the dog days of summer. I can keep them watered, I believe, to help alleviate some stress.

I hate using chemicals but I don't want any escapee bugs to get into the trees or other shrubbery. What is your feelin on using the systemic insecticide?

I have worked pretty hard to get earthworms, toads, butterflies, small birds to live in the back and I don't want anything to jeopardize that!


14 Jul, 2009


I'd like to know what borers are as well please?

14 Jul, 2009


Hi Lisann! I am also in the USA, in Florida. And I found the knock-out roses this year. They are beautiful and I don't have to fight Florida weather or bugs to keep them looking wonderful. It was recommended I plant mint in the same area as they keep out most bugs, I happen to have Chocolate Mint and no bugs. Don't know if that might help with Forsythia. But be careful, mint thinks it owns the world.

14 Jul, 2009


I'd say cut it down close to the ground and although there isn't much time for them to make new growth, if your hedge is well established, I'm sure they will come back well. You may not get the flowers next spring though. Our forsythia cuttings planted out last autumn flowered this spring. But this must surely be the best way to reduce the numbers of this pest.
Like you I don't like pesticides. I got the impression from what I read about forsythia that it was quite a resistant plant, so hopefully you should be ok.

15 Jul, 2009


Hi, Folks:

I have some very interesting news regarding my dying forsythia issue. Today, I cut a dead section of cane and shook the bugs out - they were earwigs! I believe they were just opportunists looking for a nice place to live.

But I have been e-mailing with Betsey Thomson a URI Master Gardener; or toll free USA at 1-800-448-1011 is available Monday through Thursdays 9 AM to 2 PM for live phone calls with a volunteer.

Here is what Betsey had to tell me:

"Hi! Okay, did some checking around the Plant Science department and everyone said the major problem is excess water. It's causing the pulpiness inside the stems. This acts like a blockage in our arteries, cuts off supply. The earwigs will take advantage of every hiding spot they can find. Go ahead and try the
Merit (systemic insecticide) if you want for the earwigs. Older canes do have corkiness in them but water and nutrients do seep upwards in most cases. Given excess moisture, the
insides are swelling or developing edema. Geraniums are notorious for this when given too much water and the temperature stays cool. "

This makes perfect sense since, as I stated before regarding my roses, we had a REALLY WET spring and our ground is all clay.

Now I am not sure what to do. Mold infections are starting and some white fluffy little bugs are on a few branches.

Should I still cut to the ground and let them make a comeback?


15 Jul, 2009

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