Answer: Rather than a fungus, I think you're dealing with spittle bugs. These are tiny insects that feed by sucking the juices from the stems and leaves of plants. They disguise themselves by producing a foamy, frothy covering so they won't be so evident to predators. You can control spittle bugs by washing them off your plants with a strong stream of water from the hose. They may return, but while they're in transit they won't be feeding on your plants. Just hose the spittle off whenever you see it on your plants and eventually you'll stop them.
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