Spiny Red Caterpillar defoliation of Weeping Larch tree

Question: We have a 10 year old weeping larch that has been almost virtually stripped of greenery on all of it's branches in just the past week,  I estimate at least 50 caterpillars actively feeding on the tree.  This is the first time we have ever encountered an issue like this with the larch. What should we be doing to deal with the current infestation and/or future ones. Do you think the larch will survive?  Is there any measures I should take to salvage the larch?  I have uploaded a picture of the larch tree from today (June 15th). Thank you.

responder: An Ask Extension Expert Replied June 17, 2024, 3:13 PM EDT
response: Hello Ed:  Can you send us good, clear images of the caterpillars so we can consult with the entomologist? Identifying the caterpillars is the first step before providing any kind of control methods.  We look forward to seeing additional images.

responder: The Question Asker Replied June 17, 2024, 3:42 PM EDT
response: I’m Sent from my iPhone On Jun 17, 2024, at 3:13 PM, Extension Foundation <<personal data hidden>> wrote:﻿

responder: The Question Asker Replied June 17, 2024, 3:47 PM EDT
response: Hi there, I just sent 3 good pictures of the caterpillars. Let me know if they are clear enough. Thank you! —EdSent from my iPhone On Jun 17, 2024, at 3:13 PM, Extension Foundation <<personal data hidden>> wrote:﻿

responder: Michelle, UVM Extension Master Gardener Volunteer  Replied June 18, 2024, 11:25 AM EDT
response: Hello Ed, and thank you for contacting us at the UVM Extension Master Gardener program with your question.    We appreciate you including the photos, of both the impacted tree and of the caterpillars.  The caterpillars consuming the foliage on your weeping larch are those of the spongy moth (formerly known as gypsy moth).  This is prime season (now into early July) for the caterpillars to feed and quickly grow to full size, and unfortunately they found an excellent home on your larch.    The good news is that even with that severe defoliation, most trees - especially conifers like the larch - recover and may even regrow the needles this season.  It usually takes several repeated years of caterpillar attack, as well as compounding other challenges, to kill the tree.  These caterpillars feed only once a season, so will not be back later in the year.  The tree will appreciate some extra TLC in the meantime, especially with respect to deep watering during the extreme heat in Vermont this week.    What can be done for now?   If you are not squeamish, the caterpillars can be removed by hand and disposed of in the trash or after soaking in soapy water.  If not yet 3 inches long, they may have another growth & molting cycle yet this season, so it would be worth trying to remove as many as possible soon.    There are excellent suggestions in this article by UVM Entomologist Margaret Skinner, though I can't tell if the burlap trunk wrap would be practical with your weeping larch.     https://www.uvm.edu/extension/spongy-moths  Later in the season, you can watch for the moths and any egg masses that are laid on either your larch or nearby trees.  There are more photos and detailed explanations of different control options in these other articles:   https://hort.extension.wisc.edu/files/2022/04/Spongy_Moth_2022.pdf  https://vtinvasives.org/invasive/spongy-moth-formally-gypsy-moth  https://extension.psu.edu/preparing-for-high-spongy-moth-densities  So our thinking is that this larch will survive, Ed.  If you can give it extra watering this summer to minimize additional stresses, its chances of a strong recovery will be even better.  I wish you luck with protecting your weeping larch from further attack from the spongy moth caterpillar.

responder: An Ask Extension Expert Replied June 18, 2024, 4:10 PM EDT
response: Hello Ed:  We did consult with the UVM entomologist to be sure this was spongy moth, and following is her reply:   Yes, this is a spongy moth. Also the tree should be inspected for pupal cases and egg masses later in the season to make sure they don’t recur. As for whether it will recover, this is yet to be seen. They should try to remove all of the larvae now so that any remaining needles are not consumed. Then they need to make a special effort to keep it well watered especially in this heat wave. Most hardwood trees can survive one or more defoliation, but each defoliation takes vigor away from it. This is a small tree so it will have a harder time recovering.

responder: The Question Asker Replied June 18, 2024, 4:39 PM EDT
response: ﻿Thank you so much! It sounds promising for the tree. I’ve been picking the caterpillars already.  Would an organic BT spray be helpful or be detrimental in any way? We much appreciate the quick response! —Ed   Sent from my iPhone  From: Ask Extension <<personal data hidden>>Date: June 18, 2024 at 11:25:21 AM EDTTo: Ed Giroux <<personal data hidden>>Subject: Re: Spiny Red Caterpillar defoliation of Weeping Larch tree (#0143197)  ﻿

responder: An Ask Extension Expert Replied June 20, 2024, 10:46 AM EDT
response: Hello Ed:  Here is a video that talks about spraying/control methods (scroll towards the end if you don't want to watch the entire video) -