I have several spider plants in my greenhouse which get pale grey spots, which after a few days turn to brown lumps, about 2-3 mm across. Any Ideas on the best way to treat them. I have searched for scale, as this is what I was told it is , but have had no success. Right now I scrape them off the plants. It has also gotten on a staghorn fern, and other plants as well. Thanks
Your problem sounds like an infestation of scale insects, which is difficult to eradicate, especially on soft tissues, such as the leaves of spider plants or the fronds of staghorn ferns. Scale insects begin life as minute, nearly transparent crawlers, which disperse from eggs that are laid under the adult's hardened scale-like shell. Once the crawlers find a suitable place to feed, they settle down, form shells, feed and eventually produce eggs. Control strategies should be aimed at the crawlers, as that is the most vulnerable life stage, but removing the adults (taking care not to damage the plant's tender tissues) as well, will make a difference to ultimately controlling the infestation. Crawlers are easily killed by applications of insecticidal soap (and water), but these will not affect the adults and some soaps will damage plant tissues under certain circumstances. It is best to make a test application on a small leaf sample.
