HI Elaine,  

Insect pests on redbud include aphids, Japanese beetles, treehoppers, leafhoppers, caterpillars, borers, webworms, and scale. The damage on the leaves may be caused by an insect with piercing sucking mouth parts. This feeding creates tiny, circular and discolored patches on the leaf (stippling). Look on the underside of the leaves. Leafhoopers, Treehoppers and aphids all feed on the underside of the leaves.

1.  Leafhoppers are small insects that live on the undersides of leaves. They use sucking mouthparts to feed on plant sap. They resemble cicadas and have large wings that are tent-like over the body.

2. Treehoppers are small insects that live on the underside of the leaves. They use sucking mouthparts to feed on plant sap. They are very similar to leafhoppers, but have exaggerated pronotums that may resemble humps, thorns, or spikes.

3. Aphids are small, 1/16- to 1/8-inch-long, pear-shaped, soft-bodied insects with two tail pipes (cornicles) found at the end of the abdomen. Aphids are sap feeding insects and once the fluid is digested, it is expelled as droplets of a sugary waste called honeydew.They use their piercing sucking mouthparts to feed on the underside of leaves. You can physically knock aphids off plants with a strong spray of water from a garden hose. This will also help wash off any honeydew or sooty mold that may be present.

Neem (azadirachtin) is a plant based pesticide that discourages their feeding. Insects are not killed quickly, but it makes them stop feeding and they slowly die. Insecticidal soap, horticultural oil and pyrethrins can be effective at controlling these insects. These pesticides must make contact with the insect.Once the leaves are damaged the leaves can not repair the stippling but the leaves will continue  photosynthesis to produce energy to feed the rest of the tree. Water the tree during dry spells to prevent diseases.

I can not find any disease of redbud that match the symptoms of your leaves. If you do not find insects on the underside of the leaves then do not apply chemicals.
https://extension.psu.edu/redbud-diseases

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=15420

I have been thinking about your question. It may be one of a group of fungi called powdery mildew.Powdery mildew fungi causes Infected plants to look like they were sprinkled with baby powder or covered in cobwebs. Unlike most fungi, these fungi do not require free water to germinate.  High level of relative humidity is required. Powdery fungal growth is found on the upper surface of the leaves and tends to begin on lower leaves. When powdery mildew is noticed on a few leaves, simply removing them will help with control. At the end of the growing season remove fallen leaves, which can serve as a source of infection next season. Powdery mildew does not significantly affect the health of your tree.  Fungicides are usually not needed for the health of the tree. Potassium bicarbonate is an organic fungicide that may be used to prevent infection.  Your product will control powdery mildew but could also kill beneficial insects that help to control insect pests.
https://www.extension.purdue.edu/extmedia/bp/bp-69-w.pdf  

Annabelle Hydrangeas prefer morning sun and afternoon shade. Hydrangeas like to grow in well-draining soil that is kept slightly moist. If your Hydrangea is planted in full sun, then it may need additional soil moisture.  The other plants are competing for moisture. Is it being watered deeply on a regular basis? Check the moisture in your soil by putting your finger about 4 inches down and see if there is any moisture at that level.  Slowly water with a hose near the roots to avoid wetting the leaves. If the soil is overly moist dig up one plant and examine the roots for root rot. Too much water and drought can caught this plant to dry up from the bottom and bottom leaves to yellow. Please clean up and dispose of all the wilted yellowish brown bottom leaves that have fallen off or are about to fall off. Do any of these leaves have any spots or dark areas? Examine the stems for signs of insects or disease.

Scale, aphids and mites feed on hydrangeas by piercing the plants' leaves and stems and sucking out the juices. They can cause the entire plant to wilt and flowers to fail to bloom. Do you find any sticky substance, known as honeydew, on the leaves and ground. Spray the plants with a steady stream of water every other day to dislodge these pests, or treat with an insecticidal soap or horticultural oil in the evening. Insecticidal soap can cause burn if it is used on a bright sunny day.

https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/hydrangea/

https://extension.psu.edu/hydrangea-diseases

Did anyone spray any herbicides near these plants? Herbicides can become volatile
at temperatures around 85F or on windy days.