Scale insects and southern blight must be told apart: one is a pest, the other a fungus, and the treatment is very different
The recent hot and humid weather is the peak breeding season for scale insects. Several orchid growers have already found scale insects on the leaves of their orchids, and many people still do not recognize this insect, seeing only a large patch of white powder; some growers even mistake it for southern blight and treat it with fungicides. In fact, scale insects are a pest, and fungicides will certainly have no effect on them.
As for the science of scale insects, orchid growers can look up the information themselves; reciting from a textbook is not this farmer's strong suit. I first encountered scale insects in this season the year before last, and at the time it was not on orchids. Because my family has dozens of mu of hickory trees, when I happened to inspect the grove I found large patches of white powder on the trunks of several trees, and on closer inspection there were small white insects (as in the photo above) crawling on them. So I went to the plant protection station to ask, and it turned out these were scale insects.
Scale insects have two modes of reproduction: one is sexual reproduction, and the other is parthenogenesis, meaning they can reproduce even without male insects, and they can produce several generations a year. The damage they cause to plants is great, but they also have weaknesses.
The nymphs of scale insects have very weak mobility, and their spread basically relies on the wind and on being carried by people and livestock, so there is no need to worry too much about large-scale infestation by scale insects. My method for treating the hickory trees at the time was to first scrape off all the white powder with a bamboo strip; the scale insects that fall to the ground generally cannot climb back up the tree. Then I brushed the trunks with lime sulfur mixture, and finally sprayed the area around the trees with pesticide; the treatment effect was very good.
For scale insects on orchids, we can scrape the leaves clean and apply the pesticide with a writing brush; to be safer, dispose of the white powder that is scraped off properly. In addition, spray the orchid plants with a pesticide specifically for scale insects (this kind of pesticide is available in agricultural supply stores; to avoid any suspicion of advertising, I will not name it). After this kind of control, orchids generally will not be infected by scale insects again that year.
To thank everyone for their support of this official account, Haoshe Farmer has nothing to repay you with, so he is specially offering the charcoal-dried white imperial chrysanthemums grown at home last year as gifts, with a fan lottery to be held on 2018--06--18; the number of prizes is tentatively set at 80, and each winning fan will receive chrysanthemums from Haoshe Farmer free of charge.