It all came about last week. Richard Hayden and Daniel Feldman, the Museum's garden staff, noticed that some of our Agave americana plants weren't looking so hot. Some plants had a few leaves that were wrinkled and beginning to discolor, others were so bad they weren't able to stand up straight anymore. Experimentally, Daniel tugged on a leaf of one of the sick agaves, and surprisingly the entire plant came out of the ground in his hand! What they discovered beneath the surface was not pretty. The roots had become completely unattached and the heart of the plant was a goopy mess of rottenness. Something indeed was rotten in the heart of the Museum Garden!
What sort of "evil" could cause such destruction? Weevil evil, that's what! Upon closer inspection, Richard and Daniel found an aggregation of largish black weevils (about ½ inch long) hanging out in between the plants' leaves. To be specific, they were agave snout weevils, Scyphophorus acupunctatus, and they're proving to be a big problem in the agave world.
Here's what The Desert Botanical Garden in Phoenix has to say about agave snout weevils:
"The females chew their way into the plant base, often between leaf attachments, leaving bacteria (Erwinia sp.) as they go. They lay eggs in the bacteria-infected tunnel. When the eggs hatch, the larvae burrow and eat their way into the rotting heart of the agave. After the grub-like larvae have sufficiently fed and matured they will pupate and emerge as the next generation of adults. The entire life cycle can be completed in six to twelve weeks. Adults are approximately 1/2" in length with dull brown to black stout bodies and characteristic long snouts. The rotund legless grubs are cream color with dark heads.
Most often a snout weevil infestation is not apparent until the damage is severe. As larvae start to feed at the bacterial-infested plant bases and the roots, leaves begin to wrinkle. Shriveling will increase with time and as the plant continues to rot. A putrid odor can develop as bacterial infection creeps through the heart of the plant. In many cases a majority of the leaves collapse to the ground leaving only the central spike of leaves standing. The plant might be loose if wiggled and can easily fall apart. At this stage rescue is unlikely."
When the Museum garden staff realized that this was likely the fate of many of our agaves, they, needless to say, weren't very happy. In just a short week they've wholeheartedly joined the ranks of agave snout weevil haters everywhere. Of course, they have been madly searching for ways to deal with this pest. Most of the literature out there advises continued applications of the insecticide imadacloprid. This chemical is applied around the base of a plant and is taken up via the roots which then imparts toxicity to any insect that happens to eat the plant (including pollinators when they sip nectar). Needless to say, we want to stay away from chemical pesticides as much as possible. Unfortunately, we haven't found any good leads on organic controls, but we'll keep looking.
After hearing all this, being the good friend and coworker that I am, I offered to buy the garden staff a bottle of Mezcal! No, it wasn't to drown their unhappiness in, it was instead to take revenge! The "worm" in the bottom of a bottle of Mezcal is actually very often an agave snout weevil grub. That's right, they could relish in chomping off the head of our weevils' long lost great aunt's nephew or something. Cheers to that!
Daniel removing an infected Agave americana
Daniel dissected the above agave and this is what we found inside!
Close up of agave snout weevil, Scyphophorus acupunctatus.
Even knowing the back story, I still think it's cute.