In the Garden:
Cochineal scales covers this cholla with their white waxy secretions. Red patches are visible where insects died.
Have you noticed a white, cotton candy-like fluff spreading on your prickly pear or cholla cacti? This substance is the waxy protective secretion of a very tiny cochineal scale insect that is only about the size of a pinhead.
Cochineal scale (Dactylopious coccus) has a long history of being harvested to make natural scarlet dyes. Hundreds of years before the Spanish arrived, the Aztecs were using cochineal, and soon after their arrival, it was being shipped to the Old World as a replacement for scarce and costly red dye sources. The infamous British "Redcoats" were dyed with cochineal.
Today, the scale is still farmed in Mexico (and other warm climates) where it is grown on a spineless variety of prickly pear cacti, which makes for easier harvesting. The resulting red dye is used in many products, including foods and cosmetics, as well as a natural dye for hand weaving. It typically appears on a product label as carmine or carminic acid.
Use a hand lens to view the scale up close. Otherwise, carefully scrape a bit of the white fluff off the cactus and smear it on a piece of paper or cardboard. When the female insect is smashed, you will see the bright red coloration.
Treatment for Cochineal Scale
Cochineal scale is a sucking-type insect that does minimal harm to cacti if populations are kept in check. All you have to do is hose off any white fluff periodically with a strong blast of water. Because individual insects are so tiny, and they are embedded amongst the nooks, crannies, spines, and glochids of cacti, it is impossible to remove it all with one attempt. Scale reproduces several times per year. As you see the white splotches reappear, simply hose it off again.
If left alone for years, the white secretions may eventually cover the plant, reducing its ability to photosynthesize and thrive. You may notice that the cactus is yellowing or withering. In that case, you might want to try a mild soapy water spray (one-half teaspoon dish soap to one gallon water). Sometimes, just a section of the cacti will be covered and declining. It might be easier to cut it off at the joint and discard it in the trash. Be sure to disinfect the knife or pruning tool after use to avoid spreading the scale.
A final tip: Watch out when hosing! Years ago, I hosed off a cane cholla thick with cochineal scale while wearing old whitish sneakers. They were pinkish when I finished. If there is a considerable amount of scale on your cacti, the water will run off or splash red, so wear old clothes. Unless your goal is to dye your outfit, of course!
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