Currant leaves turning brown

I have several currant bushes that are having problems. They are in full sun most of the day which probably isn't ideal. The soil is a somewhat loamy clay more clay than loam covered with mulch year round which is primarily chipped leaves and wood chips about 2 inches deep depending on how it's breaking down. Did a soil test about a year ago. Most minerals are in the high range mostly due to the clay.

First I suspected spider mites but I don't see any signs of the little buggers. I see no evidence of an insect issue.

The brown leaves are spreading to all of the bushes. One bush has very few leaves left and those are going fast.

Any suggestions?

Are you experiencing the heat wave we are getting here in Texas?

You have not said anything about how much water the plants are getting.

Lack of enough water would be my suggestion.

Yes it has been hot for about the last month, some 80s but mostly 90s and a couple 100s.

They get irrigated water once or twice per week depending on if we get rain. I usually go for infrequent but heavier watering. The soil seems generally moist at least the top inch but with that said I was just planning on getting out the moisture meter and probing around.

Edit: Moisture meter says moderately moist though we've had about 1/2" of rain in the last 2 days. First time we've had a significant rain in the summer since 2019.