Agave Snout Weevil

[Gee.S]

Weevil

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Weeviled

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Agave Snout Weevils.pdf

Snout Weevils.pdf

[Gee.S]

I usually go weeviling mid-March, then again mid-May per DBG regimen, but it does make sense to bump that up a bit, considering how warm it has been. With more than 200 Agaves in the ground, this is a major chore that may take me 2-3 days to complete.

[Gee.S]

I rotate two 5-gal buckets and unceremoniously dump a bunch of imidacloprid water on plants by hunch/feel. Nearly the whole bucket for my largest plants. Very unscientific, but knock on wood, I haven't lost a plant to weevils yet, and they're dropping like flies all around me. I just try to think how much water if I were hand watering all my plants this way...

[mcvansoest]

Hi Ron,

Yeah my approach to the snout weevil treatment is very similar. For the smaller plants I use a watering can and for the large plants a bucket. For the smaller plants I use the stuff that is more of an on leaf/plant application while for the larger plants I use one that is best administered around the plant so it can absorb through the roots.

[Gee.S]

An important note regarding the application of imidaclorprid as a drench, per recommendation. Pesticide instructions for snout weevil are absent on product labels, and those references available on labels seem difficult to interpret for this kind of application.

I was instructed long ago to mix 1 oz. per gallon of 1.47% solution (this is a fairly standard mix), then water plants as if one were watering normally by hand. I don't know if this is ideal, but it is effective and does no apparent harm to Agaves. I do know this seems rather vague in terms of chemical quantity applied, but understand that Agaves tolerate imidaclorprid extremely well, and can withstand a dose larger than intended without suffering damage.

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[center]Special note of caution: Do not treat bolting/blooming Agaves, and please take every precaution to avoid runoff directed toward nearby plants of any kind that may bloom within a few weeks of application. We do not want treated blooms passing toxins onto our pollinators.[/center]

[mcvansoest]

Not the greatest picture attached here, but this is a close up of the damage done both by bacterial rot and the weevil grubs and weevils themselves. This was a big Agave weberi that I did not treat for weevils because it was bolting. The stalk got to about 20 feet tall just about to start developing its panicles before the damage got so bad that the top of the plant including stalk completely fell over.

I fully agree with Gee's treatment process, but given our mild winters here I am considering adding a Fall treatment to the late Winter and mid Spring treatments as I suspect that this plant got infested in the late Fall rather than late Winter. The last two winters here in Mesa we have probably had three nights at or slightly below freezing total which makes we wonder if weevil activity just does not slow down in such cases.

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[Melt in the Sun]

Time to treat! Found a couple of these little bastards in one of my blue glows.

[Melt in the Sun]

'tis the season! This guy was already dead...preemptive treatment is always best.

[mcvansoest]

Yeah, it is on the to do list, am late this year - very few Agaves growing in other yards close to the new place which means what I have in the ground is either fine or they are all 'it' already. Seen no signs though.

[abborean]

'tis the season! This guy was already dead...preemptive treatment is always best.

I know it's late to comment on this MITS but the adults bore into the bud and the larvae eat down into the base. If you just see them eating a little hole in the top they can be stopped from killing the plant with your usual systemic.

[bigdaddyscondition]

Melt, sorry you lost that beautiful A. impressa (?) to the evil weevil. I'm looking at mcvansoest's August 15, 2017 comment in this thread, and I am nodding my head in agreement. One imidacloprid drench in the springtime has protected all my agaves for the last several years, until this year.

A couple of months before this A. gentryi 'Jaws' (see photo) began showing any sign of spiking (sometime in August), the central leaves lost turgor, with several leaves narrowing, wilting, and even bending over. I suspected weevil infestation despite my having treated the plant in March with imidacloprid drench, the unceremonious dump technique of Gee. So I immediately treated the plant again, and I suspect I arrested the weevil activity, if not the bacterial rot. The plant is still obviously viable, and I still see none of the classic proximal leaf pallor and loss of turgor.

Lessons learned:

1) Agave gentryi 'Jaws' is one of the species that the agave snout weevil prefers. This suspicion of mine was confirmed by John Trager, Curator of Desert Collections at the Huntington, in a phone conversation last month.

2) In my area at least, more than one treatment per year is necessary. Going forward, I plan to treat all my agaves with an imidacloprid drench in the fall, in addition to the March treatment I've been doing.

3) Mature agaves that are about to spike seem to attract the weevils. I suspect this is because of the high concentration of carbohydrate nutrients in the meristem and developing inflorescence. It also presents the dilemma of whether to treat a plant that soon will flower, offering imidacloprid-tainted nectar to pollinators. Increasingly for me, the solution to that problem has been to cut down the stalk before it flowers.

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[mickthecactus]

There is some suggestion this pest may have arrived in the UK possibly via Portugal.

[Melt in the Sun]

Pulled apart a rotting mangave 'Mission to Mars' to find some late summer / early fall weevils. Out came the spray and soak buckets! I found a couple adults on plants nearby, so hopefully I am not too late.

Anyone know of a reference for the life cycle of these bugs? I see grubs and painfully slow adults, and wonder how they manage to find plants especially when there are very few other agave around my house...

Out of curiosity, I kept pulling the core apart until I got it clean. I've wondered in years past if this could re-root and continue growing, which means you could keep growing a rare plant if weevils got it. We'll find out!

[bigdaddyscondition]

Sorry about your plant, Melt. I hope you can save it. I haven't seen any references on the life cycle of the agave snout weevil. Sounds like a good dissertation proposal for a grad student.

I just did my fall imidacloprid treatment of my agaves in September. Next treatment is in March.