Help! Some of my Agaves and Yuccas have rotted at the base and collapsed, only to find a mushy and decayed mess. What is causing this?
It’s an attack by the Agave Snout Weevil (Scyphophorus acupunctatus). The picture above shows the adult and the grubs which were embedded in a Yucca aloifolia plant and the damage they cause.
This is a nasty little creature, ½ to 1” long, black, wingless, with a typical weevil snout that bores holes into the base of more mature agave, yucca and other related plants with a base diameter of 2” or more.. Then, it introduces a bacteria which is necessary to cause rapid tissue decay in the plant to feed its white legless grub larvae at the same time it lays its eggs. Once hatched, the larvae feed on the rotting and bacterial rich inside tissue of the agave plant causing it to eventually collapse. It then pupates from larva to adult in the surrounding soil. If this pest is not discovered early on, there is little one can do to save the plant.
OK, now what you may need to do to prevent this nasty creature from destroying your Agave and Yucca plants is apply a systemic insecticide (liquid or granular form) that is effective on grubs. Bayer Advanced Tree & Shrub Insect Control, with the active ingredient imidacloprid (under the trademarked name Merit) has been used effectively. Recommended treatments should be in spring and once absorbed into the plant, should protect your plant for up to a year. Treating the surrounding is also necessary. Other systemic insecticides can be used if they are recommended for treating grubs. Always follow the directions on the product labels. As much as I hate to use any chemical product, this unfortunately is the only effective way to combat the Agave Snout Weevil once discovered. Observation and immediate removal of infected plants and soil around them is also effective in combating this pest. Agaves grown in containers with sterile soil are much less susceptible as the weevil is soil borne during it’s development. This weevil is doing much damage to commercial Agave crops in Mexico (Tequila, Sisal), therefore is having an economic impact as well. Ironically, it is this grub that is often placed in the bottom of a bottle of Tequila.
Next time you enjoy a Margarita raise your glass and say “Curses to the Agave Weevil”