Southern Utah Cactus and Succulent Insect Pests

In recent years I have seen an increase in Agave Weevil Damage, Cactus Longhorn

Beetle, and Scale and mites on our prized desert plants. Here are some things you

can do to identify and control these insects in your landscape.

Agave Snout Weevil

‘Gonzo’ snouted insect can be seen laying eggs in the spring and

overwintering in the fall. It is commonly confused with Billbug snouted insect which infect our grasses. Key identification differences are: in the Agave Snout Weevil, the adult is about . inch in length, is brownish black and has a dull body. Whereas, Billbug Weevil bodies are dark brown with speckles on the abdomen. The adult agave weevil attacks many species of agave. The larger Agave such as the Century plant is more susceptible to weevil damage than the smaller species. The adult female enters the base of the plant to lay eggs. Decay microbes also enter through this injury and as the tissue rots, the plant has a wilted appearance. Infested plants soon collapse and die. The larvae (grubs) who are also feeding on the decaying areas, continue their lifecycle, developing within the dying plant and infect other hosts nearby. Also witnessed is that this agave snout weevil also infests the canes of several Yucca species. Control of the agave snout weevil is difficult. Selecting species that are less susceptible andtypically smaller than the century plant is helpful, especially in areas where the problem has occurred previously. With special specimens, chemical prevention using a broad-spectrum insecticide such as Sevin or malathion applied every 15 days in March and April is often effective in reducing damage. Systemic insecticides which are carried into the plant through the roots is also an effective control and can last up to 3 months.

Cactus Longhorned Beetle

cactus longhorn beetle attacks several species of cacti including prickly pear and cholla cactus (Cylindropuntia species), barrel cactus (Echinocactus and Ferocactus species), young saguaro cactus (Carnegiea gigantea), and others. The adult beetle is about 1 to 1. inches long, shiny black, and has distinctive white markings on the antennae. The antennae are often longer than the overall body length of the adult beetle. Damage to the plants is the result of feeding on the margins of prickly pear pads or terminal buds of other cacti. Adult beetles survive winter as pre-pupae around the base of the cactus. They transform to the pupal stage in spring and adults emerge in late spring and early summer. Adult beetles feed at night, typically eating young cactus pads or oozing sap. After mating, the females glue eggs to the cactus pad. The young larvae attempt to tunnel into the cactus, causing the plant to ooze sap at the wound. The young larvae first feed in this ooze, later entering the plant. They feed throughout the summer and early fall. One generation is usually produced per year, but some of the later larvae may not emerge until the second season.Cholla cacti are attacked by the beetle when the adults lay their eggs, hatch and the larvae burrow into the stems. Waste is pushed out the entry holes and forms a black crusty deposit on the canes. Larvae

burrow into plant roots and cause collapse and death of the plants. Due to its size, Cactus longhorn beetle is usually easily controlled by hand picking the insects off infested plants. The beetles are most active and easier to detect and destroy in the early morning or late evening, especially after warm summer rains. Very spiny species are less likely to have damage from the beetle due to a natural defense by the spines. Chemical control is usually not needed. However, broad spectrum insecticides can be applied to the base of the plants in the fall, where the beetles lay their eggs.

Scale Insects

Prickly pear (Opuntia species) and cholla cacti (Cylindropuntia species), are

attacked by cochineal scale. Agave has a specific scale called Spider Scale that is almost indistinguishable from the actual agave leaf. Armored Scale also infect desert plants and are usually found on the undersides of leaves or in shady crevices where new growth attaches to the main plant. Cochineal Scale, the most common scale in our area, covers itself with a waxy coat that makes it appear as white cottony tufts attached to the pads and stems of the cacti. To positively identify cochineal scale, crush the waxy coat with a your finger or a pencil eraser. If the result is a deep red material-actually the body fluid of the insect-then it is cochineal scale. Cochineal scale is still used by native peoples as a source of red dye and also as a natural food coloring in processed foods. Spider agave scale and Armored scale are less common. They may weaken a plant but seldom will cause death. However, their secretions do create a condition called Sooty Mold which is generally thought to be a fungus and can increase the likelihood of the plants decline if left untreated over several years. Scale usually can be controlled by using a strong stream of water to wash the insects and their ‘sooty’ secretions from the plants. If the infestation is heavy or the insects return, an application of insecticidal soap may be needed. As scale insects feed on the living tissue of the plant a systemic insecticide can be effective if used in the spring.

Mite Insects

Agave mites and Spider Mites are another important pest to watch out for. Still less common than our previous pests. Mites are tiny 1/50 of an inch insects that feed on agave, yucca, and cactus. They leave speckled indentations and can reduce the health of your desert plants. It is highly unlikely that mites would be the main cause of a plants death. Although they are often blamed. When a plant is weakened due to overwatering, under-watering, poor planting depth, freezes, or other stressful situations the plants defenses are down. Mites can have better success in building their colony on such plants. They are usually a secondary, or opportunistic, pest and swoop in just in time to notice a plant decline. Thus, they become the scapegoat in many cases. Bottom line is get out and walk around your yard every month to see what, if any, activity is happening in your plants. Keep your eye open for these critters. If you see something out of the ordinary or some yellowing on your agave, don’t dismiss it until its too late. Investigate further over the next few days. In most cases you can reverse the problem in the earlier stages of infestation. If you would like to hire out this responsibility send me an email I know a few landscapers who are doing it right and would love your business.