Not Bonsai LILAC BORER

[j evans]

I need some ideas as I have a 30 year old lilac tree that has borers. The tree has been going down hill for the last couple of years but I thought it was because of winter damage. Now I see that it has borers (sp?)
It is about 90% gone and I see that it has about 8 - 10 holes that I can find. I am thinking of chopping it below the lowest bore hole and hope that it sprouts. Has anyone tried this or attempted to get a lilac to recover from the borers? I don't want to spend the money to have the yard crew inject it. Thanks for any ideas.
Jamie

 

[Leo in N E Illinois]

Years ago I got rid of borers in a landscape lilac by exactly that method. Cut lower until you see solid stems with no holes beneath the solid wood.
You can cut lilac down to the ground, new stems will shoot up from the roots.

Burn or remove all infected wood right away. Don't leave infected wood lay around.

 

[Leo in N E Illinois]

Systemic pesticides will also work. Read labels, only use if it lists borers as a target pest. Local box stores should have several options by Bayer or Bonide. Read labels. Must list borers.

 

[j evans]

Leo - now I really feel stupid and bad. I always keep the Bayers in the garage for my roses so I have had it around for years and I have just watched the tree deteriorate. Now that the tree only has about 20 - 30 leaves I Don't know if it will suck up enough of the medication. I have seen at least 6 or so holes. Your opinion?

If I have to/or choose cut the tree when would be the best time? I would assume early spring but can the tree survive that ling with the bugs? We are just starting into cooler temps.

Thanks for your help and time.
Jamie

 

[Jzack605]

If it’s truly 90% gone no systemic or chemical will turn it around and save the tree. Your only chance now is a hard cut back as stated.

 

[j evans]

When?

 

[Jzack605]

I would recommend late winter-early spring. Leave as much as you can, but they are hardy and can take a lot of abuse. You may not get flowers for up to three years is one potential downside.

 

[Leo in N E Illinois]

When?
You don't want the borers to successfully over winter, I would cut as soon as the lilac is fully dormant, say middle of winter. Before ground thaws in spring

 

[Jzack605]

Only issue with mid winter is cold drying winds/air and open wounds. They will have a harder time healing. Doing closer to growing season begins allows plant easier chance to rebound and heal. They borers may overwinter but as long as they are cut back enough it shouldn't be a problem. The borers shouldn't even be close to being active early spring and you can confirm this by measuring the growing degree days and cross referencing with the pests required amount to come out of dormancy. Lot's of resources will outline how many GDD it takes for them to be active again. If you have not ID'd the type of borer you can view all likely species and play it safe by picking the one that becomes active first. Not as difficult as it may seem, there should be a GDD calculator for your area and easy to read chart with pests and their corresponding GDD.

 

[j evans]

What if you cut, sealed and wrapped the cut in fabric or the like to protect from the winds. Wouldn't the borers also be completely dormant during the winter?
What about cutting now? Too close to cold weather?
Thanks

 

[Jzack605]

I wouldn’t cut now, and I wouldn’t recommend sealing cuts for a landscape plant. It seems to be a touchy subject for bonsai, but for landscape plants pruning seal has been proven to have no effect and even detrimental effects. Let normal plant functions heal these wounds. Your best bet is to wait, and do in early spring just before dormancy ends and growth flushes begin. Your lilac at this point is deacclimating and preparing for dormancy. I would let it get that last bit of energy stored.

 

[rockm]

When the weather gets colder, the borers will go dormant.

I'd wait til early spring to prune the lilacs to the ground (there is a hedrow of 250 year old lilacs near me that have been repeatedly chopped to the ground over the years. They come back with new growth. FWIW, borers can be symptoms of a larger problem that is weakening the plant. Look for other stressors, like mucky soil, hard compact soil, browsing deer etc. That may be the problem you need to solve.

 

[j evans]

The soil is not ideal as it is a hard clay but the plant thrived about twenty years prior to this problem. It is producing some suckers so I hope that a cutting with some babying it might recover. My grandma had grown it as a tree and gave it to me about 23 - 24 years

 

[Jzack605]

Lilacs are hardy and can take various soil types but like any plant can only take so much. Consider working some compost into existing soil and mulching. It will make a tremendous difference for the health of the plant. Regardless do fertilize with an organic fertilizer same time as cut back.

That it is still sending up suckers is a good sign.

 

[j evans]

I have been sitting here patiently waiting but stewing about this chop. From all the input I am thinking that about the middle of February will be the surgery date. I have one more question to throw out, should the cut be flat or slanted? And if slanted should the top of the cut be where I want the new sprout? Any other suggestions or comments?

 

[Jzack605]

Flat will be fine.

You're in a pretty cold zone, at least colder than mine. I still think waiting a bit longer would be better, so give it some thought and don't let impatience get the best of you. You seem to really want to ensure the survival of this tree.

 

[j evans]

In January when the weather got better I did a chop on the trunk. I did it below the lowest borer holebI could find. The weather then turned bad again. Once it turned decent we have a sprout. I also treated with systemic medication. Hopefully with the sprout we are on the way. I am only sorry that it took me so long to find the problem.

 

[j evans]

Good news
And it is still growing.