Answer: It's difficult to recommend a treatment strategy without knowing precisely what's attacking your orchids.
Since they're outdoors, they may be infested with spittle bugs. These tiny insects suck the juice out of plant tissues, causing wilting of stems. The pests manufacture a spit-like substance to hide themselves from predators. If your orchids have blobs of white stuff that looks like spit, you can wash the pests off with plain water.
Other common pests include cottony scale and mealy bugs. these have a fluffy white appearance. Again, they're sucking insects and can cause wilting of stems. These pests can be removed by carefully dabbing or rubbing them off with a moistened cotton swab.
Finally, a fungal disease like powdery mildew might be what's causing white patches or blotches on the leaves and stems of your plants. Fungus is hard to control, but you can start by removing the affected plant parts. Then move your plants around so there's better air circulation among and between them. Mist your plants everyday to help discourage powdery mildew.
Hope your orchids regain their health!
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