also, I think it may be important to mention that I am in Barbados, which is tropical for those of you who dont know. So its warm/hot and sunny all year round with a fair ammount of humidity. also the plants get about 6/7 hours of full sun a day, after that its diffused sunlight till the sun sets.

For spider mites and aphids, blasting them with water every day for three days straight should start to take care of the problem. Odd if it is spider mites, they usually like dry, not humid.

For fungal diseases (powdery mildew and blackspot are the most prevalent), try a Google search for the Cornell Formula or modified Cornell Formula.

Here is a link that might be useful: Cornell Formula