At this time of year with such high temperature and little or spotty rain, you could be watering every day.

Tithonia or Mexican Sunflower can be susceptible to common leaf spot diseases just like your zinnias and other annual flowers, especially in our humid summers. Your first photo shows what looks like an old, dying leaf- just remove it. Similarly to our zinnia answer, regular grooming, or removal of the worst affected foliage is recommended. This removes some pathogen from the area as well as makes the planting look better.

Again, it is not possible to positively i.d. the actual pathogen from photos alone (nor is it necessary) but these plants are most commonly affected by Cercospora (fungal) leaf spot, which shows up as small tan to brown lesions surrounded by a reddish-purple border. Eventually, the center of the lesion may drop out leaving a hole. Older infected leaves may yellow and die. The disease is more noticeable when conditions are warm and humid. Quite possibly Alternaria as well.

Again this is usually at the bottom- can be groomed out and the flowers keep going.

In case you see this response first, here was our answer on the Zinnias, (and will be similar for your Borage):

"Zinnias are gorgeous but can be afflicted with leaf spot and other diseases like powdery mildew in our Maryland landscapes.

The best way to deal with these issues is to choose zinnia varieties that have been bred with some resistance to disease. For instance, 'California Giant' likely grow cleaner in that state than in our humid climate. A disease replacement could be 'Benary Giants'.

Other management techniques, such as how to keep the leaves drier (and remove the most diseased leaves and flowers) can be found on this page from N.C. State Extension: https://hgic.clemson.edu/factsheet/zinnia-insect-pests-diseases/ We do not necessarily recommend the same chemical treatments here however.

Horticultural oil products or fungicides can be used but are not curative, they just slow the infection down and need to be repeated- not a great alternative.

After selecting resistant plants, it's best to place susceptible plants where there is adequate sunlight and good air circulation to reduce humidity levels. Allow proper plant spacing for the same reasons. Pruning for better air circulation also may help."