Common Agave Pests

Plants that seem the most cast iron can indeed have an Achilles' heel. Just like so many mighty giants of history it is often the littlest things that ultimately bring them down.
By: Maureen Gilmer
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This mature variegated form of 'Agave americana' is vulnerable to snout weevil and sudden meltdown, as are most of its close kin. (SHNS photo by Maureen Gilmer / DIY Network)




The great agave meltdown began at summer's end. I thought I'd simply watered them to death, but in this sandy soil that is downright hard to do. And when it's 110 degrees outside the surface evaporation makes over-watering virtually impossible.

My beautiful blue striped "Media Picta" and golden "Variegata" are gorgeous forms of their parent species, Agave americana. This is the big blue agave that is so resilient it's planted as living fences in dry climates where they seem to live forever. But mine suddenly wrinkled, went flat and all the roots vanished in a matter of weeks.

I discussed it with succulent guru Clark Moorten.



The snout weevil is named for its pointed proboscis, which it uses to chew a hole into the soft center of the agave before laying its eggs there. (SHNS photo by Maureen Gilmer / DIY Network)

"Agave snout weevil," he said, to my great dismay and relief. At least it was not my heavy handed watering. "Beetles start it and the grubs finish them off. It's why tequila is so expensive all of a sudden. They devastated the blue agave in Mexico."

I yanked one of the last agaves out of the ground to find the offenders still inside the fleshy stem!

Like exposed termites, an inch long black beetle and a writhing, fat white grub were hunkered down in the fissures chewed through stem tissue.

Armed with field proof I scoured the books. Lo and behold, the grub proved to be the very worm found in bottles of tequila from Mexico. Eating them is a drunken rite of passage for college party animals.

More fascinating is the life cycle of these pests. In just 60 to 90 days they go from eggs to larvae to pupae to adult beetle. The beetle crawls into a healthy agave rosette and punctures the soft inner column of compressed leaves with its distinctive pointed snout.

Look close for these quarter inch brown edged scratchy marks and holes because that's the only outward sign of impending meltdown.

Appropriately enough the insect is named Scyphophorus acupunctatus. Its bite deposits a nice little dose of bacteria into dense living tissue, which spreads so rapidly it is the true cause of death. The beetle lays its eggs in the same area.



This type of white grub made famous in Mexican tequila bottles feeds on tissues that connect roots to the heart of the agave, cutting off the plant's moisture supply. (SHNS photo by Maureen Gilmer / DIY Network)

Eggs hatch into small caterpillars that feed voraciously on the softened bacteria-decayed tissues. Grubs can grow to the diameter of a pencil and cause extensive damage to the heart of the agave severing the roots from the stem. The grub reaches maturity and pupates into an adult beetle which starts the whole cycle over again.

My Agave americana cultivars are among the weevil's favorite subjects while very hard leaf medium to small species are less attractive. After the meltdown I realized that very few large plants could be found growing in my area proving widespread vulnerability. Control of the beetle is nearly impossible because they are protected from pesticides by a dense succulent plant.

In an effort to find resistant ornamentals, growers are watching for exceptional survivors in beetle plagued areas. It is said that if an individual of a vulnerable species reaches the final age of flowering, then it is probably weevil resistant. The vegetative offsets or "pups" around its base will be genetic clones that carry the same resistance as their parent.

In Mexico small tequila agave farmers once cultivated their own resistant clones culled from generations of crops. When they were replaced by large corporate monocultures of a single genetic clone, agave azul, the weevil had a field day. It caused up to 40 percent of the crop to melt down in some areas.

As gardeners, the process of learning never ends. Sometimes lessons are painful. Plants that seem the most cast iron can indeed have an Achilles heel. Just like so many mighty giants of history it is often the littlest things that ultimately bring them down.

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