According to some reports we are going to have a hot, wet summer. Wet foliage and high humidity encourages the spread of fungal and bacterial diseases. Bacterial diseases do not respond to fungicides and vice versa so it's very important to know which disease you are dealing with. Perhaps the easiest way to distinguish between the two is by smell. The most common bacterial disease in orchids produces a foul smell often likened to dead fish. If you've ever had cut flowers stand too long in water you know the sort of smell we're talking about. The best control is provide lots of air movement, water early in the day and try to keep the leaves dry.
If we have a hot, dry summer then low humidity presents a few different problems - possible dehydration, sunburn and the ever-present spider mite. If the heat and dryness is accompanied by wind the risk of plants drying out is exacerbated. Plants will dry out very quickly and may need watering every couple of days. Monitor your plants carefully and get to know the feel of a dry pot. If the pseudobulbs start to shrivel you have probably lost the roots. Daily (or more frequent) misting helps to boost humidity and that may help with the next problem.
Mites LOVE dry conditions and tend to thrive in colonies on the underside of the leaves sucking the sap from the cells. I direct my misting wand to the underside of the leaves to discourage the tiny blighters. If you do find evidence of them - silvering of the leaf on the underside or even a fine web - wipe the leaves with white oil. If it is a large outbreak you may need to use a special miticide spray.
Solar radiation is much more intense in the summer and plants that have been happily in full sun all winter may need extra protection (shade) when the sun is the strongest or, often during the late afternoon when the temperatures are highest. Orchids are easily sunburned and while sunburn is not in itself a serious problem it is irreversible and will make your plants look ugly. In serious cases the plant can be killed outright and any leaf damage is an invitation to a secondary infection in the damaged area.