Hey there, so i don't know much about the defguard but its label looks slightly intense. I know I've heard of many people (industry and homegrowers) that use hydroguard as the sort of "standard" product..but it essentially does the same thing.
Have you ever used any silica products alongside the spray applications? Because it's a great way of strengthening the plant and helping it fight off PM as well as other diseases...especially if you use it in your regular watering schedule, not just once(potassium silicate is most known). Just a thought as something to help the plants. ✌️ Happy growing