Agave snout weevil is in the neighborhood

Once upon a time, my friend Darell, who lives a couple of blocks away, planted an Agave americana ‘Mediopicta alba’ much like the one below:

Agave americana ‘Mediopicta alba’ in our garden (removed last year because it was encroaching into the sidewalk)

A while ago, Darell had noticed that his Agave americana ‘Mediopicta alba’ didn’t look so hot: The lower leaves were turning black, and the upper leaves had begun to shrivel at the base. He doesn’t water very much, and initially he thought it was because of that.

When I stopped by his place yesterday, I suggested he remove his Agave americana ‘Mediopicta alba’ and plant something nicer instead. For fun, I kicked the center of the agave with my foot. It wiggled so much, it was immediately clear that it wasn’t attached to the soil any longer. A stronger push with my foot knocked the entire plant over, exposing this gruesome sight:

At the bottom, a hole in the ground. At the top, a spongy mess:

When I lifted up the remaining bottom leaves, we saw them. Dozens of them, scurrying from the light:

A quick Google search confirmed my suspicion: agave snout weevils, having the time of their short, but oh-so-destructive, lives.

As nasty as the adults are, the larvae are even worse. Play this short video and you’ll see what I mean:

I had heard anecdotal reports of agave snout weevil sightings in our area. But I hadn’t seen any myself, so I was hoping they hadn’t made it to our part of town yet. Clearly, that isn’t true anymore. The snout weevil is in the neighborhood.

Once restricted to Mexico and the desert Southwest, the agave snout weevil (Scyphophorus acupunctatus) has rapidly spread into Southern California and northwards from there. Measuring approximately half an inch in length, it has a downward-curving proboscis which allows it to tunnel into the core of an agave, leaving behind bacteria (Erwinia carotovora) that cause the surrounding tissue – and eventually the heart of the agave – to decay. Once inside, the agave snout weevil deposits its eggs. When the larvae hatch, they devour the rotting center and then burrow into the soil to pupate, eventually emerging as adults.

Some agave species are particularly prone to infestation. Agave snout weevils seem to prefer Agave americana, especially older plants and variegates, as well as other large agaves like A. franzosinii, A. ovatifolia, and A. weberi. In contrast, they tend to avoid agaves with soft leaves, like A. attenuata; agaves with tough leaves, like ‘Sharkskin’ and victoriae-reginae; and agaves with slender, non-juicy leaves, like A. bracteosa, A. geminiflora, and A. filifera. In spite of its name, the agave snout weevil can also infest manfredas, yuccas, furcraeas, and other plants in the agave subfamily.

There is no treatment for agaves already infested by the snout weevil; the only option is removal. Before you plant another agave in the same spot, drench the soil with an imidacloprid solution. Imidacloprid is a systemic insecticide that is absorbed by the plant through its roots and then translocated throughout the plant tissue. It kills sucking and boring insects by contact and ingestion.

Drenching the soil with an imidacloprid solution in the spring and fall is also the best method to prevent infestation. Debra Lee Baldwin has detailed information on her excellent website.

Back to Darell’s Agave americana ‘Mediopicta alba’. This is what was left after we had removed the bulk of the plant: an “octopus” of desiccated leaves.

Earlier, after I’d pushed over the top of the agave, we could hear clicking sounds coming from the hole in the ground – as if an underground army of weevils was working in overdrive. Darell says that after the carcass of the agave had gone into the yard waste bin, the beetle sounds were ever louder there. Somehow that made the whole experience even more gruesome.

On my recommendation, Darell drenched the area with a goodly amount of imidacloprid solution to kill any adults and larvae still remaining in the soil.

I will do the same in my garden, especially after losing several agaves recently (see this post). Until yesterday, I had blamed their demise on the recent heat dome. Now, I’m not so sure. Maybe the two large ones that died, Agave chazaroi and Mangave ‘Mission to Mars’, were actually killed by snout weevils? I didn’t see any adults or larvae, but that doesn’t mean they weren’t there.

If you want to learn more about the agave weevil, below are a few useful articles.

MORE INFORMATION

• Agave Snout Weevil, Coming to a Garden Near You (Debra Lee Baldwin, Gardening Gone Wild)
• Agave Snout Weevil Prevention and Treatment (Debra Lee Baldwin)
• Agave and yucca weevils—Scyphophorus species (University of California Statewide Integrated Pest Management Program)
• Agave Snout Weevil—Desert Gardening Guide (Desert Botanical Garden, Phoenix)
• Agave Weevils: a Water-wise Gardener’s Nightmare (SF Bay Gardening; info of particular interest to Northern California gardeners)

© Gerhard Bock, 2024. All rights reserved. To receive all new posts by email, please subscribe here.