Ask Mr. Smarty Plants

Bignonia capreolata (crossvine) is a lovely, versatile native vine. The prolific spring blooms can be a real knock-out. Your brown leaves may or may not be a severe problem.

There are several possibilities. Your vine has clearly flourished for a couple of years, which suggests that it was planted in an appropriate site and your southern exposure should encourage blooming. Has anything changed to negatively affect the plant? Are other plants encroaching? Does it get more or less water than formerly? Do broadleaf herbicides get applied where they could affect the vine?

Crossvine can be evergreen, but in some winters it loses its leaves even down here in Texas, and you are closer to the northern climate range for the plant. To check and see if the vine itself is still alive, scrape away a bit of the bark on a main stem. The interior bark layer should be alive and green. If it is not, your vine may have died back. In that case, I would cut it back and hope that its root system is still viable. You could feed it a mild tonic, like a seaweed infusion, nothing too strong that would shock it. It could very well come back, and maybe more vigorously.

Since this plant is several years old, another possibility is that some of the vine's older growth just needs to be rejuvenated with some pruning. Cross vines are most vibrant and productive on new, younger vines, flowering on new growth. Brooklyn Botanical Garden, which is in your climate zone, has a Vine Pruning Guide which recommends late winter or early spring pruning for Bignonia capreolata. While they point out that minimal pruning is required, Crossvine is a vigorous climber that you may want to prune to control its size and direct its path. Benny Simpson, on the Texas A&M Native Shrubs Database suggests light pruning after flowering to extend the flowering season.

Here is a link to a previous  Bignonia capreolata (crossvine) query:

What is wrong with my crossvine (Bignonia capreolata)?

Hope this helps.