When a tree is dug for transplanting, it can lose 95 percent of its root system. The lack of rain  this season means that the tiny root system is unable to take up enough water. Your crab apple trees may have transplant shock. This condition is common in newly transplanted trees as they try to establish a new root system. Mulching and extra watering will help your tree recover.

Before you irrigate a tree, check to see if the soil is moist. Get a shovel or a metal rod and go 8 inches deep. Water only if the soil is dry. We want to keep the soil moist but not soggy. A slow watering is best to make sure the water goes to the tree roots and does not run off. You can water with a Gatorbag . Another way to conserve water is to mulch the area under the crown with 2-3 inches of wood chips. Do not pile up mulch and create a volcano effect. Instead, create a donut shape that creates a hole, with little to no mulch touching the base of the tree.

https://www.extension.purdue.edu/extmedia/bp/bp-31.html

https://www.ag.ndsu.edu/yardandgardenreport/2016-07-13/trees-in-shock



Water and mulching with 2-3 inches of wood chips under the crown will benefit all trees.   The following site has disease information that might be of interest to you.

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