If you find this plant infestation in your garden, here’s what you should do

Gil Martinez, who gardens in Encino, sent me pictures of a prickly pear cactus (Opuntia ficus-indica) infested with cochineal (KOTCH-ih-neel) scales. Martinez was concerned since he has a sentimental attachment to the plant, having grown up with nopales (the edible cactus leaf pads) in Mexico, the prickly pear’s habitat. The scales in question, white in color, are often mistaken for a fungus. They also bear a close resemblance to mealybugs, which are actually a kind of scale, except that adult female mealybugs have motility – that is, the ability to move around their plant hosts at will. Other female scales — including cochineal scales — are basically sessile in their adult stage, meaning they attach themselves to stems, leaves, or fruit and stay in one place as they suck sap.

Cochineal scales are famous for carminic acid, which constitutes approximately 20% of their bodies, and is used in the manufacture of red dye. This metabolite helps them deter ants and is toxic to potential predators. Certain moths, however, do make the scales part of their diet, becoming toxic themselves to moth predators in the process. The abdomens of female cochineal scales, which contain their eggs, are especially concentrated in carminic acid and dye manufacturers are skillful in separating pregnant females from the rest of the scale population.

Carminic acid has multiple uses. As a food colorant  (E120 or Natural Red 4), it is found in frozen fish, meat, beverages of all kinds, yogurts, ice cream, candy, ketchup, and canned soup. It is also found in cosmetics such as eye shadow and lipsticks. A small percentage of people are allergic to these dyes and therefore, by law, products that contain them must be labeled as such.

From the middle of the 16th century, when the Spanish first found the Aztecs using carminic acid as a red dye for fabrics, until the middle of the 19th century, when synthetic dyes were developed, the cochineal scale was the main source of red dye throughout much of the world.

Prior to that, the main source of European red dye was the kermes scale that infested the Mediterranean kermes oak (Quercus coccifera). This textile dye had been in use since biblical times. In the book of Exodus, a fiery dye used in the Tabernacle tapestries was said to come from a “scarlet worm,” which has since been identified as the kermes scale. However, the scarlet dye extracted from the cochineal scale was eight times brighter than that produced by the kermes oak scale, and so that the former took the place of the latter in the manufacture of red dye.

A completely infested cactus pad should be cut off in its entirety at the joint. Salvage partially infested pads by blasting the scales with a pressure hose. Even if the scales are not knocked off the pads, this procedure will compromise their waxy protective covering and weaken them. I recommend the utilization of a hose attachment that adjusts the stream of water from a diffuse, gentle spray (excellent for watering newly planted seeds) to a powerful jet, which is the adjustment suitable for scale removal. Alternatively, you could scrub off the scales with a brush, attached to a long stick or pole if the pads have thorns. (Note: Although the leaf pads of wild prickly pear cactus have thorns, there is a thornless prickly pear, bred by Luther Burbank, as well.) Scales that remain attached after a hose blast or vigorous scrub can be finished off with a dish soap solution (1 teaspoon of dish soap per gallon of water) applied from a spray bottle. Should scales still make a return, you can repeat the above treatments after ten days. Be aware that prickly pear cactus exposed to full sun is less likely to develop scales than when it is growing in some shade.

A number of years ago, Nick Kurek from Granada Hills sent me simple instructions for preparing prickly pear fruit (tunas) and pads (nopales) for eating. “The flesh of cactus pears,” he wrote, “is sweet and flavorful, even if seedy. Needles come off the fruit by rolling them in the dirt, and then they can be peeled.”  As for the pads, “cut the young ones only, slice off the spines (if present), dice them and then boil them with onions. Serve either hot or cold.”

Speaking of insect pests, “The Vegetable Garden Pest Handbook” (Cold Springs Press, 2021), by Susan Mulvihill, is excellent, more instructive regarding its subject matter than any I have seen. The photographs alone make it a worthwhile addition to any gardener’s library. Insect pests are shown up close on the plants they inhabit along with the damage they do. “Mugshots” of beneficial insects are also included.

Although organic chemical remedies are thoroughly discussed, the author recommends them as a last resort, noting that organic sprays may kill certain beneficial insects and pollinators along with the pests. Besides, patience alone may sometimes solve an insect problem.

“A few years ago, I was walking through my garden and stopped to check on the currant bushes,” Mulvihill writes. “When I saw a lot of puckered leaves, I inwardly groaned. Aphids. I turned over some leaves. Yes, lots and lots of them were on the undersides. I debated about what to do but decided I didn’t have the time at the moment. You guessed it. My schedule got busy over the next few days and I completely forgot about those aphids. A few days later, I suddenly remembered them and dashed back out to the garden. Instead of witnessing more aphid mayhem, I was pleasantly surprised to discover that almost all of them had vanished. In their place was a collection of adult ladybugs, their larvae, and even some pupae, which are essentially pre-adults.”

One way to prevent aphids and cabbage loopers (that turn into white butterflies) from bothering your cabbage family plants is through the use of bridal veil netting, or tulle, as opposed to more typically used, yet opaque and somewhat suffocating, row cover. “Since these crops benefit from good air circulation, I’ve found the netting works better than regular row cover. It also allows me to more easily see what’s going on under the cover without having to lift it and peer underneath. You can purchase tulle by the yard at fabric stores or by the bolt from online suppliers. Be sure to buy a very fine mesh with tiny holes because aphids are small and sneaky.”

Among the practices that the author recommends to keep insect pests at bay are crop rotation, reflective silver polyethylene mulch (makes it difficult for pests to find their target plants), planting flowers that attract beneficial predator insects among your vegetables, and constructing insect hotels. “Once you build an insect hotel, you’ll soon discover that watching it is both fascinating and cheap entertainment.” Incidentally, scales are not mentioned in this book because they choose their hosts (shrubs and trees) for the long haul and therefore leave annuals, whether flowers or vegetables, alone.

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Several readers responded to my enthusiastic advocacy for planting oleanders – now that oleander leaf scorch disease is under control – with a caveat regarding the extreme toxicity of these plants. If you are roasting marshmallows, for example, never use oleander stems as roasting sticks. Grazing animals have died from oleander ingestion so it would be advisable to keep pets at a distance from them. Lucky nut (Thevetia peruviana) is an oleander relative with an even more toxic reputation. It is distinctively ornamental with shiny green foliage and silky yellow flowers.

Tip of the Week: Vinca (Vinca rosea or Catharanthus roseus) – in pink, red, lavender, or white — is an oleander cousin that is a staple of the flower garden despite its toxicity. Pets that eat it get seriously ill so make sure to keep them at a distance from it. Having said that, under the right circumstances, no plant is more rewarding. Although usually grown as an annual, vinca will live for several years where soil drainage is good, half-day sun prevails, and watering is an afterthought. My neighbor has had a planter full of vincas for more than two decades. They flower abundantly year after year with little effort on his part. The plants grow to a height and width of around three feet and drop seeds that germinate in place. Also known as Madagascar periwinkle, this plant shares its African island habitat with snake plant (Sansevieria trifasciata) along with many other species that are legendary for their drought tolerance.

Please send questions, comments, and photos to joshua@perfectplants.com.