Ask Mr. Smarty Plants

The first possibility is that the leaves are chlorotic; that is, they don't have enough chlorophyll, which can cause black spotting between veins in the leaves. Plants can become chlorotic because the soil in which they are growing is so alkaline that the plant has difficulty extracting the iron that it needs from the soil. In the Austin area, particularly with other mountain laurels growing nearby, it seems unlikely that too much alkalinity is the problem. However, chlorosis in the Sophora secundiflora can also be caused by overwatering or watering too shallowly. This particular plant requires very good drainage and is accustomed to growing on limestone shelves or in very rocky soil. If your affected mountain laurel is in a low spot, a spot that accumulates moisture from runoff, or is watered by a sprinkler system, but not thoroughly, that could be causing the symptoms you are observing. Check the drainage on that tree; they need only be watered (if there has been no rain) every two to four weeks, but need to be deeply and thoroughly watered then. We think this is probably the most likely culprit.

We found several references to the genista caterpillar, apparently the larval stage of the Genista moth. Read this article on the Sophora Worm from the Maricopa (AZ) County cooperative Extension Home Horticulture site and see if any of the symptoms match the ones you are observing. Apparently, just picking off the caterpillars and/or destroying the webs that are spun by them controls that problem. If, upon close examination, you feel this is your problem, the website says you probably don't need to worry about it, but does give suggestions for control if the problem becomes severe.