I had to look to see what zexmenia was! It seems it's a host plant for the Bordered Patch Caterpillar. But maybe you know that since you planted it.

Your photo in the Flickr page wasn't large enough for me to confirm if the caterpillars are spikey like the bordered patch ones are. (Just Google Border Patch caterpillar images and you'll see tons of photos.)

Since I'm not familiar with the plant, I don't feel qualified to guess what it's ailments might be. If all else fails, I guess I hope you'll get some beautiful butterflies from this experience! Good luck!

Welcome to the wonderful world of zexmenia hispida! A beautiful, tough little plant with pretty flowers for much of the year and requiring little (if any) maintenance.

I looked again, but the caterpillars are too small/immature for me to properly identify them as Bordered Patch. But if they are, then I'll tolerate them so long as they don't eat the whole plant. And hopefully they will stick around after they mature!

Anybody else able to identify the disease that is ailing my other zexmenia plant?

No wonder the Bordered patch butterflies are always hanging around the zexmenia! I didn't know it was a host plant for them. They certainly like to nectar at the plant. The plant is so full and large that I've never noticed anything eating it. The deer don't like it so that's a plus.

Sorry I can't positively ID the problem with the foliage. Could it be mildew because it's not getting enough sun? Mine is planted next to the street between two driveways in full all day scorching sun and does very well there. Another plus is that it is evergreen.

Here's a picture of the Bordered patch butterfly on Sweet almond verbena:

I have several zexmenia and my experience is they don't like shade as much as is reported. I have had issues with mine in shade and have since moved all that I have into at least 1/2 day full sun. I never watched mine that closely - I have had stunted and misshapen leaves, but chalked it up to too much shade. I doubt they will die - probably come back from the roots after a while. I never have issued with the ones in at least 1/2 day sun. I've never had 1 die either. They are tough plants!

This is the first year I've seen the delightful Bordered Patch butterflies on cosmos and also the first time my native sunflowers have been covered in their larvae... moved some to horseherb which is also supposed to be a host plant.

Here's a photo of the larvae. Wasps got many of them already.

Annie at the Transplantable Rose

Here is a link that might be useful:

Thank you so much for the photo of the caterpillars so we'll know what they are when we see them.

Gardenhorn:
I have had a few problems with Zexmania hispida now known as Wedelia texana.
Your problem sounds like spittle bug they leave behind the
mildew looking residue. Being they pierce the plants tissues this causes branches to die and sometimes the entire plant.
The other problem I have seen is Lacebug (common on Lantana) the plants stop blooming and has a stunted look to
it. Spittle bug can be killed by pinching the "spit" and
killing the insect inside. Lacebug is killed with Insecticidal Soap. Hope this helps
Art

My zexmenia likes the shade and part shade just fine. Strange. I never planted it . It grows naturally wherever it wants.

Thank you all for the responses. I went out there this morning to get a closer look. The caterpillars are Bordered Patch (so I will tolerate them).

However, I looked at the bottom of the leaves and found some white residue (kinda fuzzy). The link below will have more pictures of it.

I haven't found any insects on it (though that doesn't mean they aren't there). But I'm now leaning towards this being a fungal disease. This all started after we got a lot of rain at the end of June and beginning of July. Plus, this is in my backyard, where there is less wind due to the fence. Plus, my zexmenia are planted in a raised bed (excellent drainage), so the border acts as an additional barrier for wind. And, the underside of leaves are affected on the mature leaves while the top side of the leaves appear normal.

But then again, I could be wrong. Do these new pictures help anyone identify this problem?

Here is a link that might be useful: More pics of my Zexmenia on Flickr

I have the same white whatever they ae on my zemenias also. They seem to be imbedded on the underside of the leaves. I cannot scrath them off. I haven't gotten rain in the Texas heat of 106 degrees but I did spray them a couple of times in the evening. I have made many online seaches and cannot find out what they are. I have tried Neem Oil mixed with soap with no results. I have many Zemenias mixed inbetween other deer and draught resistent plants in my front yard and back yard. The other plants show no signs of these white things but all of the Zemenias have them.

Like you I am hoping someone can help with identification so a remedy can be made.