Infested Joe Pye Weed

9 years ago

I got four Joe Pye Weed divisions from an old neighbor this spring. About a month after planting them, I noticed white patches on the leaves. I brought them to a local nursery, and she cut open the spot and found an insect crawling inside of it. So, I guess it is some type of leafminer or other insect that opens the leaves and lays eggs inside of them. She suggested just removing affected leaves, which I did. But every time I remove the affected leaves more and more appear to the point that the plants are very sparse, and even the ones I have left have small white spots, though I suspect they will get bigger as time goes on. I thought about digging them up, but I really like their appearance and height. I went to another nursery and she suggested a systemic insect drench. PLEASE do not lecture me about using them; I understand the downsides. I rarely if ever use chemicals, and I feel terribly guilty for using it, but I felt that if I could use it once or twice and eliminate the problem it would be worth it to keep the plants. I was at another nursery today and brought up the problem and the woman suggested just getting rid of the plants and said that I will have the problem year after year. I am NOT willing to constantly be using the drench.

Has anyone had experience with this? Can the problem be eliminated in an application or two, or will this be an ongoing problem that requires treatment every few months. If so, I will just remove them and try to find something else that is not as susceptible to insect infestations. She said Joe Pye is particularly susceptible. I'm concerned about it affecting other plants as well.

I've attached a picture of a leaf. Thanks very much.

Comments (4)

rhizo_1 (North AL) zone 7
9 years ago
Yes, that is a leaf miner. Shame on that nursery worker for suggesting a systemic pesticide for a plant so attractive to such a wide variety of pollinating insects and hummingbirds.

Leaf miners are difficult to control and using a systemic won't solve the problem. If your plants are as infested as you say, I wouldn't hesitate to get rid of them. The pollen and nectar is not healthy anymore, anyway.

In the future, should you grow it again, timely applications of Neem oil can help deter the tiny leaf miner flies from laying eggs.
Kimmsr
9 years ago
While the leafminers make the leaves they inhabit appear not very attractive they do not do much harm to those leaves. Although some sources suggest pulling the affected leaves off the plant unless the larva is still in the leaf there is no really good reason to do that. Control is pretty much limited to the adults that lay the eggs, and systemic poisons do little to control the larva, although some sources will state that if systemic poisons are used they need to be applied about two weeks before the larva start to feed on the interior of the leaf.
Since these larva are the hosts for a number of parasitic insects I'd not do anything about them since topical poisons to control the adults will also kill those parasitic insects.
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ken_adrian Adrian MI cold Z5
9 years ago
you are in z4 ...

its basically sept ...

wont your plants be freezing to the ground in weeks???

cut to 3 to 6 inches ... mulch in oct...

remove refuse from property ...

really now.. chemicals.. this late in fall .. not in my world ..

same thing i just did with moms phlox.. heavily infested with powdery mildew ...

pshaw on the person who wants to sell you product ...

see what happens next year ... if it comes back ... since it is a z5 plant ...

ken
angt29 (Minnesota, zone 4b)
Original Author
9 years ago
Thank you very much for the replies. I think I will just get rid of them. My cardinal dogwoods have some type of leafminer as well, but they are leaving very narrow trails, so I'm not very concerned about that damage, which seems more typical to leafminers? Whatever is on the Joe Pye is decimating the leaves until they are completely white, black and crunchy. They must be hardy here because I got them from someone else who has had them for years in zone 4a. At any rate, I will pull them (sadly) and find something next year that will thrive in about six hours of sun and has a lot of height. Any suggestions? Thanks again.