What are the remedies for excessive paclobutrazol application?

I recently saw in the ChineseOrchid, 1994 Issue 6, Comrade Pan Zhijing raised the problem of applying overly concentrated paclobutrazol causingorchidsto stop growing, and Comrade Gu Jun answered it in 1995 Issue 3. I would also like to share my views here. When it comes to paclobutrazol, we must first connect it with plant hormones. There are five major hormones in plants, and gibberellin is one of them. One of the physiological functions of gibberellin is to promote cell elongation, causing the plant to grow taller and the leaves to lengthen. Gibberellin can only be biosynthesized in plants through a very complex process. Through scientists' research, paclobutrazol inhibits the enzyme activity of three steps in the gibberellin biosynthesis process, so the gibberellin content decreases and plant growth is delayed. Paclobutrazol is a gibberellin biosynthesis inhibitor, not a poison. After applying overly concentrated paclobutrazol to orchid plants, the following methods can be used as remedies. First, after paclobutrazol is applied, the orchid plant absorbs it into its body through the roots or leaves within a short time (from a few minutes to more than ten minutes), and washing with water cannot wash it off. If no treatment is given, paclobutrazol in the orchid plant body will gradually decompose into substances with no inhibitory effect, and the plant will slowly resume growth. At the fastest it takes half a year to a year, and at the slowest two to three years, depending on how much paclobutrazol the orchid plant has absorbed. Based on the principle that paclobutrazol inhibits gibberellin biosynthesis and causes the plant body to lack gibberellin, after excessive paclobutrazol application, a gibberellin solution of 500-1000 ppm can be sprayed, once a week, and 2-3 times will be enough. As the gibberellin content in the body increases, the orchid plant can resume growth. Second, changing the growing medium is also a necessary measure. The residual effective period of paclobutrazol in soil is very long, generally from half a year to a year or even longer, of course related to soil texture, temperature, and rainfall. After spraying overly concentrated paclobutrazol, the pot and growing medium can be changed, discarding the growing medium containing more paclobutrazol and replacing it with new growing medium containing no paclobutrazol, and the orchid plant can then grow normally. Third, on the basis of spraying gibberellin, applying urea and potassium dihydrogen phosphate solution can promote growth. Finally, a reminder to orchid growers: when using plant growth regulators, the concentration must be considered carefully, and it is better to use a dilute solution than a concentrated one (generally 100-1000 ppm is suitable), and it is better to spray 1-2 more times. When applying, first use one or twoorchidplants for a preliminary test, and only after three to five days, if there is no burning or other abnormal phenomenon, apply it on a large scale. [Editor's note: Professor Pan Ruichi is a professor in the Department of Biology at South China Normal University, Shipai, Guangzhou, Guangdong Province, China, and is the first doctoral supervisor in China to take orchid physiology as a research subject. The first doctoral student he trained, Mr. Ye Qing, whose research topic was orchid physiology, stayed at the university to teach after graduation and is now an associate professor.](Pan Ruichi)