Ask-a-Dave's-Gardener: What is killing all my plants??, 4 by Apeachg

Apeachg wrote:
I’m not sure if it’s an issue of overwatering, underwatering, or disease. We have had really hot weather the last week or two, so I’m not sure if I overwatered to compensate and/or if they have disease, or if it was so hot they need more water?! It’s affecting my iceberg and climbing roses, pomegranate, pittosporum, almost everything! I noticed a light grey insect on one of the roses, not sure if it’s a pest or not. Help!!