Growers often compound their problem of high temperature damage by turning on the drip irrigation at mid-day. The temperature of the water in a black emitter tube line laid on soil in direct sunlight can reach scalding temperatures. With the low flow rates of most emitter systems a grower can easily apply a gallon of 120 degree (or more!) water to each plant in the yard. This effectively sautees the fine shallow feeder roots - disaster!
Watch out for this pattern - the hops bines get progressively shorter and yellower away from the main feed.
Consider adding some aerial sprinklers - which is the proper way to cool an overheated hopyard. Run them in short cycles before mid-day as cold water applied to hot leaves causes damage.
Setting up your hopyard for an expected scorcher of a day is easy to do - just do it early! Mis-use of your watering system causes further plant damage, stalling of growth, and kills your yield potentials.