You could try spraying with insecticidal soap early in the season and see if that prevents or at least minimizes the leafhopper damage, but because the potato leafhopper has multiple generations through the summer your Ptelea could be re-infested from other sources.

Here's a good article from the BYGL: Wafer Ash Leaves Fading to White (interestingly it includes a photo of a Giant caterpillar on an infested leaf).

There aren't many wafer ash around here, but we have plenty of prickly ash and Giants are fairly common. But with those nasty thorns and suckering habit prickly ash certainly isn't for everyone's yard. Years ago I had a small Evodia (Tetradium daniellii) in my yard and observed a Giant laying an egg on it. Unfortunately I had to remove it the next year (it was killed by ambrosia beetles). I also once transferred a Giant caterpillar from prickly ash to a potted curry tree plant (Murraya koenigii), and it finished its development and made a chrysalis.

Giant Swallowtails are common, and expanding their range. Since they are not a threatened species, you can remove the wafer ash trees without worry or guilt. Although you will likely have fewer swallowtails visiting your yard, the benefits of removal appear to outweigh that negative.

gyr_falcon, My impression is that in more northern regions the number of Giants is linked to the local abundance of the food plants that are native here (wafer ash aka hop tree, and prickly ash). I believe the OP is in central PA(?), so not sure how common these two food plants are in that area. Are you in CA? Are Giants out there in the far west now considered a separate species (Papilio rumiko)?

caterwallin, I was just organizing emails and found some from you circa June 2013. The New Jersey Tea are still only about 1.5 feet high. They are flowering right now. Used to hope they would take off but now I'm just glad they stay alive and do their thing.

I have fifteen GST eggs on my hoptree that is in the ground (versus the potted ones). The tree has a zillion potato leafhoppers on it. Thought that maybe my bug zapper tennis racket might thin the zillion. It did very well. I held the racket perpendicular to the branches and then hit the branches. Leafhoppers flew up and got zapped. Now I have half a zillion leafhoppers. Going to get the ladder out tomorrow so I can get the higher branches.

KC, I hope that your butterfly season continued to be okay. The leafhoppers were worse this year than I've ever seen them, and to think that I didn't used to see them at all here as far as I can recall. It sounds like in the past you had those pests pretty bad too. They sure have showed up in droves here. As it turns out, I guess I didn't have to be concerned about the GSTs not having any edible wafer ash leaves because the GSTs never showed up here to lay eggs. I saw one here one day but them it was gone. I hope that those darn European hornets didn't get it. I saw some Monarchs lying outside that they killed. We didn't used to have them here either and now for about the past ten years they've been showing up here girdling our lilac bushes and killing the butterflies. They patrol the butterfly bushes looking for some to kill. I've killed a few, but who wants to be out there with Raid every day to do that! We've even tried using those traps that are made for them to get in, but they didn't do much good. I don't think I saw these pests either until I started getting into butterfly gardening or a few years after. Actually, I first planted milkweed in 2005 so it's been over ten years that I've been into it. It just doesn't seem like so many years have gone by already.

Wow, I didn't realize that it was that long ago that I sent you those NJ tea bushes. I'm sorry to hear that they haven't grown much in all that time. I wish there was something I could tell you, but I haven't gotten a clue as to why they wouldn't have grown very much. Mine are probably three feet or so high and look really healthy. My daughter found some Cecropia cats on them last year or the year before (I forget), but unfortunately they all ended up dying even though they seemed to really like them. I didn't find them listed as a host plant for them though.

Thanks for that tennis racket bug zapper idea. I know just what you mean. My son had bought one several years ago and it hasn't even occurred to me to use one. I'll have to try that next year because I believe that the leafhoppers have left now for the year, I think so anyway.

I forgot to mention that this was a really bad butterfly year for us, no GSTs to raise, and we didn't have any Pipevine Swallowtails to raise either. Overall, we haven't had nearly close to the amount of butterflies this year that we had other years. I hope this isn't a bad sign of things to come.

Arbordave, I don't usually take so long to reply to people commenting to me, but I'm obviously getting forgetful because I forgot that I started this thread until I noticed it today when I checked to see if anyone was interested in the butterfly cage that I'm finding a home for. I saw your reply to gyrfalcon and you're right, I'm in central PA about an hour above Harrisburg. I actually don't know how common wafer ash is around here and I hadn't actually heard of the tree before coming here to the butterfly forum some years ago. I have at least six wafer ash trees and I planted them probably close to ten years ago by now. I've been keeping them to an accessible height and what leaves are on them now are really looking in sad shape because of the leafhoppers.

I've never tried spraying the trees with anything as I assumed that anything I'd put on the tree could kill any GSTs that would come along to lay their eggs. I didn't have any show up to lay eggs this year at all. This has been the first year in ten or so years that we haven't gotten to raise Giant Swallowtails and the same goes for Pipevine Swallowtails. It's been a very disappointing years.

Thank you for the link to the article about wafer ash trees and leafhoppers. I started reading it and will go back and finish it; it looks very interesting. I don't have any prickly ash, as I guess I'm one of those people for whom those aren't desirable trees. I don't know if there's a particular reason why I've always had an aversion to thorns but have always passed on thorny trees and bushes for our yard. Sometimes I even wonder if I should have planted the eight paw paw trees that I did some years ago; I wonder the same thing about the pipevine, as it has a tendency to spread quite a distance from where I planted the plants. If the lawn goes without mowing for awhile, we have dozens up dozens of pipevine sprigs of pipevine coming up for probably up to at least thirty feet away from where the three plants started out when I planted them.

I'm not familiar with that Evodia that you say a Giant laid on, so I'll have to look that up. It's too bad those the ambrosia beetles killed it. I wonder if that and the curry tree plant are listed on the host plant page on here. I'm not sure how to get to it anymore and probably the last time I looked at it was back when this forum was Gardenweb before it became Houzz. Larry Gene has always liked to keep track of host plants on that page and he'd list the host plants for butterflies after people on the forum would report that he/she raised them on a particular plant. I was just curious if you had reported the Giant cats on those plants that you mentioned.

I have no idea why my original username for the forum shows up on some of my posts like it's supposed to and why my real name shows up on other posts that I make. I just noticed that. I didn't have that happen before today. Anyway, so as to avoid confusion, I am indeed Cathy Brouse alias caterwallin as I made up that username years ago when I joined the forum. I just don't post nearly as often as I used to. I guess that because I've gotten into butterfly gardening more and more over the years, it has limited my computer time and other things as a result.

I hope that Giant Swallowtails are expanding their range like you say. I'm always thrilled to see a Giant here, but unfortunately I've only seen one here this year and either it was a male or a female with no eggs to lay because we never found any eggs on our GST host plants here. I don't even know if it's possible for a butterfly to recognize their predators and avoid the place because of it. I've wondered if they were here briefly and noticed that our yard has European hornets, which are trying to destroy our lilac bushes. It was very upsetting for me to see some remains of Monarchs lying out in the garden at places where I highly suspect they were ambushed by these marauding hornets.

I wish I knew of a successful way to rid this place of the hornets because it makes me mad and feeling kind of guilty for attracting the butterflies to my yard and garden by planting host and nectar plants for them just to have them killed by the hornets. Maybe it's my imagination but they seem to especially go after the biggest butterflies like the Monarchs and swallowtails. I don't know if they ever do kill the smaller ones like the many Silver Spotted Skippers that we usually have here, but I don't recall ever finding any of them lying around here dead. If the butterflies are avoiding our place because of the European hornets that are hanging around, I certainly can't blame them for that. I miss having the numbers of butterflies here that I used to have, but I don't want them being picked off one by one by those disgusting hornets. They are BIG and I suppose could pack a wallop if a person would get stung by one. The lilacs that the hornets are determined to destroy (and also that the Tiger Swallowtails love) have been here since before we moved here about 30 years ago. I've always enjoyed the fragrance from them. I'd hate to have to take them out in an effort to discourage the hornets from showing up at our place, but they might end up killing them eventually anyway because I've been noticing the hornets at them pretty much every day for quite awhile already.

It makes me angry that I've done so much work to attract butterflies here and sometimes I sort of wish that I didn't have some of the plants that I have because they sometimes indirectly cause the death of the butterflies. In some cases, maybe not the death of them, but it sure doesn't seem like the plants are helping the butterflies in some cases, as in the case of the wafer ash trees being taken over by the leafhoppers, leaving what I'd think is little edible foliage for the Giants. It's just too bad that the leafhoppers are so attracted to the wafer ash trees that I planted here for the Giants. I've been feeling very discouraged this year because of the small numbers of butterflies and because of the increases year by year of the pests that negatively affect the butterflies. I sure hope that next year will be better, and I hope that other people aren't noticing the decreases in butterflies like has happened here.