“a good horticultural soap spray” – name one, please
https://www.gardeningknowhow.com/ornamental/cacti-succulents/christmas-cactus/christmas-cactus-fertilizer.htm provides a fantastic amount of information and URL's. However, unfortunately, there is no footnote for "a good horticultural soap spray." Please, (1) consider an edit for that; BUT (2) identify one or more examples of a specific product name. AGAIN, it is obvious that 'you' love plants but plant-owners more. It is devastating to have a plant you are nurturing facing death or die! Thanks for all the people who give such detailed advice.
Certified GKH Gardening Expert
We don't recommend product brands. You can ask friends for a recommendation or try different ones to see what works best for you.
You also can make your own:
Use a natural soap product without synthetic additives or perfumes, which can be found in local natural food stores. Combine one heavy tablespoon of liquid soap to one quart of warm water. Tap water is okay to use, but if you have hard water you may want to substitute bottled water to avoid any soap scum buildup on foliage.
Read more at Gardening Know How: What Is Horticultural Soap: Information On Commercial and Homemade Soap Spray For Plants https://www.gardeningknowhow.com/plant-problems/pests/pesticides/homemade-soap-spray.htm