By Scott Calhoun
Just as our plant palette differs from the rest of the country, so does our menagerie of pests and diseases. Animals and viruses sometimes rudely eat, disfigure, and prey upon even tough desert plants. Focusing on pests that attack succulents, cactus, and agave species, the pests below make up my Most Unwanted list:
Cochineal Scale (Dactylopius coccus)
Also known as cottony scale, this parasitical insect lives on prickly pear cactus. It is easy to spot—white, cottony dots, resembling random polka dots, appear on pads. If you were to squeeze the cottony substance between your fingers, you would produce a blood-red juice. This scale is cultivated commercially in Mexico as a dye for food, clothing, and cosmetics, but in your garden it can make your prickly pear plants quite unsightly. The good news is it rarely kills them. (Photo: Christine Hoekenga)
Control for chochineal scale: The best approach is to spray off the scale with a strong jet of water, repeating frequently until no more white fluff reappears. In the worst case, discard the infected plant and start again.
Agave snout weevil (Scyphophorus acupunctatus)
This one can be deadly to your prized century plants. The female agave snout weevil, a black beetle with a hooked nose, lays her eggs in the stem of usually mature plants. The eggs hatch into grubs that voraciously consume the plant and roots from the inside out, until only a central cone remains, with the outer leaves flopped on the ground.
Control for agave snout weevil: I use garden pesticides reluctantly, but the only sure way to prevent losing some susceptible plants is preventively applying a robust systemic insecticide (often called systemic “grub killer”). However, once you see the outer leaves flop, it usually is too late to save the plant. Century plant species that tend to be most prone have wide leaves, such as Agave americana.
Agave running bug (Caulotops barberi)
Named for the way it runs and hides beneath leaves when approached, this tiny piercing/sucking insect may go unnoticed at first. Running bugs leave small, stippled dots, as shown in the photo, right. If left unchecked, an infestation can be fatal.
Control for agave running bug: With some quickness and skill you can squish running bugs. But there are often so many of them, or they hide so well, that an insecticidal soap or neem oil applications works best.
Javelina (Tayassu tajacu)
Also known as a desert peccary, this animal strongly resembles a wild boar but is a large rodent that travels in herds. They usually rest in the day and appear at night. Javelinas are known to forage on oak acorns, so beware if you have an oak tree. The animals also are fond of pumpkins, and especially like the fleshy roots of newly planted hesperaloe, spineless varieties of prickly pear cactus, and other succulents. Do not approach javelinas—they have sharp teeth and poor vision, and occasionally attack humans and dogs if threatened.
Controlling javelinas: The best way to keep new plantings, such as hesperaloe, from being eaten is to securely cage them with hardware cloth or chicken wire, anchored to the ground with rebar. Don’t leave trashcans out at night, as javelinas are known to topple them to eat their contents. It is also unwise to leave jack-o’-lanterns out at night because pumpkins are irresistible to these hoofed invaders.
Find out what our 10 regional gardening experts are dealing with these days—pests, viruses, and even beneficial insects.Learn More