Thursday, June 30, 2016

"Yuck-a" weevil takes a toll in my garden!

This is a bummer post, just so you know.   A few weeks ago while investigating why a formerly healthy row of Yucca 'Color Guard' plants were suddenly dying from the ground up I discovered holes in the base of the plants.


Agaves and yuccas have been the backbone of my landscape since I began working on this garden in 2009.  After all, they add so much and require almost no attention from the gardener.  Just plant and walk away.   About the only problem I knew of is what I had read in blog posts like "Evil weevils" from Digging on the demise of agaves and related plants from agave snout weevil attacks.  So when I discovered the damage, I knew just what it was.  Snout weevils had bored into the core to lay eggs and their larvae ate the fleshy insides on their way out leaving cavities in the base of the plant from which it cannot recover.  I removed the infected plants and surrounding soil, placed them all in tightly closed trash bags and deposited it all in the trash.

Before, we had three cheerful matching Yucca 'Color Guard' looking great along the driveway


After, not so great.


Surveying the rest of the garden I found several soft-leaf yuccas (Yucca recurvifolia) looked yellow around the base and literally broke off in my hands as I checked them.  This meant I had to take fast action.  Following the advice I found in Pam's post and verified through other sites we began to treat all agaves and yuccas with a systemic insecticide from Bayer with the trade name "Merit."  I rarely reach for the bug killer, but these plants represent a huge investment in time and money.  You can read more about the product at Tropical Texana.  Early spring is apparently prime time for infestation and the best time to use a systemic is in advance so I'm not sure how effective a late spring/early summer treatment will be.

It wasn't long before I noticed the sudden decline of one Beschorneria in a pot by the garage and found larvae holes in the base.  Oh no, not the Beschoneria!  Oh yes, it's toast.


At this point I found the larvae and a few weevils or beetles in the soil.  Warning:  Ugly scenes ahead!

Telltale holes in the base.  How supposedly flightless insects found their way up into a 20" tall pot is a mystery.



Rotten core


While I didn't capture any weevils, I found larvae.



For some reason the other Beschorneria is fine.  Since these were matching planters on each side of the door and I won't purchase another Beschorneria I'll move the remaining plant elsewhere.  Then I'll need to find something else for these pots.  I trimmed those yellow leaves after this photo.


And onward we go into the back garden where I have had to remove all my Manfreda 'Macho Mocha' and surrounding soil.  Is it the work of the actual Yucca or Agave Weevil?  Must be, I was too busy stomping and squishing to take an ID photo of the culprit but we noted two different types of beetles in the soil around the affected plants.  Manfreda 'Macho Mocha'  is described on websites I read as being particularly susceptible.

Larvae still wriggling in the core


This is not a Yucca weevil which is less shiny has a pronounced snout but it was in the soil as we pulled out plants.  Perhaps an opportunist taking advantage of holes drilled by another beetle.  I couldn't get a good look at the other darker beetle or see the snout.


Another Yucca recurvifolia in the crevice garden is toast.  One positive note is native Manfreda maculosa and Yucca rupicola or Twist-leaf yucca plant seem to be unaffected so far.  Fortunately a coveted Manfreda 'Chocolate Chips' Pam shared with me from her garden this spring had been potted up and placed inside the sunny screened porch and is just fine.  Not that pots are a barrier since the Beschoneria was in a pot but I think the combination of being on the enclosed porch and in a pot seems to have helped save it so far.

We're not done yet.  While checking the crevice garden for more yucca damage I noticed  Agave 'Blue Glow' had telltale signs of yellowing bottom leaves.


Even though most websites ID the Agave weevil as different from the Yucca weevil, there seems to be no difference in the damage.  Either I have both types or they are indiscriminate.


Ewww!



More plants and soil into the trash.

So now my agaves are under attack and I just brought home a new Agave Cornelius which will need to be protected.  Agaves are slow-growing so the chances they will take in enough systemic during summer's heat to ward off attacks from borers are slim but I will continue to treat and check.  And hope I have eradicated the little (bleeps).  At least I read they slow down in the summer.

Agave 'Blue Glow' with Bluebonnets in happier days.  We will miss this plant which was a favorite in the crevice garden.


How did these bugs get here?  Did I bring this culprit home from the nursery?  I have no idea.  All affected plants have been in the landscape for at least three years.  Since my only recent agave or yucca purchases are unaffected, I'm fairly certain it didn't hitch a ride to my garden from a nursery.   However it got here, there will be no more soft-leaf yuccas, manfredas, or agave relatives added to the garden for a while.

Resolving this issue may take years considering the massive numbers of beetles across our entire property.  Given the size of this infestation and the rapid takeover it's unlikely I could have stopped it unless I had been proactively feeding insecticide to my plants for the last year or two.  Drenching soil with systemic insecticide "just in case" is simply not the way I garden.

It's not easy watching so much of our planning, work, and enjoyment of the garden unceremoniously pitched in the trash bin.  Even as I continue to dig out plants and soil, I'm already moving past this and thinking what to do.   Summer heat is upon us now so I'll take some time and decide what to replace all those missing plants with.  I was so happy with the way things looked that it's hard to imagine not having these softer forms of spiky plants in prominent spots.  Some plants are less susceptible than others and I'll compile a list which will more than likely include a few of these Agave schidigera 'Shira ito no ohi' which seems less susceptible to the weevil.


Besides that, this plant just makes me smile.

12 comments:

  1. OH NOOOOOOOOO!!!!

    Shirley, I am so sorry to see this! That's so awful. What a complete swath of destruction. I was just thinking the other day that I ought to preventative treat my agaves and yuccas, and now, believe me, I am motivated. I am so bummed for you. When you're ready to add more agaves & yuccas, please let me know. I've always got all kinds of pups to share. Knock on wood.

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    1. Oh Lori, you are so sweet to offer pups from your garden. I think the best course is preventative treatment and that's the route I'll take from now on. Once it hits there's not much time. Since spring is the prime time for these beetles, starting now should be plenty of time to protect your plants.

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  2. That is just terrible...so much damage...I'm so sorry :-(

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  3. Shirley/Rock-Oak-DeerJune 30, 2016 at 9:50 PM

    Thank you Scott, we'll get past this and find some great new plants to fill the gaps.

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  4. Ouch!! That's quite a deal of damage. So sorry to see this.

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  5. I am so sorry! My brother in Phoenix has had both yucca and agave attacked and flattened at the same time. I don't know that he ever figured out if it was the same pest or not. Either way he lost a lot of plants. I hope you've caught it in time to treat and prevent further loss and heartbreak.

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    1. I found your post on the problem. It will be a wait and see thing from this point. I try to take stock of the remaining plants each day to dig out any remaining issues ahead of time.

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  6. Ugh, that's awful! I'm so sorry! What a mess. :(

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  7. That's terrible! Hideous creatures! Now you have me wondering if the problem I just noticed yesterday with 2 Cordyline 'Electric Flash' in my back garden might be related. I hope I'm just being paranoid. Best wishes with the eradication process.

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    1. There seem to be a number of borers with a taste for different plants so it's possible though a search didn't turn up anything on cordyline.

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  8. All that devastation and you are still able to smile...I like that about you!

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  9. Oh no :( evil weevils! Nasty things. Glad to hear your positive note at the end. Onwards and upwards with the garden!

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