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Thursday - January 27, 2011

From: Melbourne, Australia
Region: Other
Topic: Cacti and Succulents
Title: Scale on Agave attenuata from Melbourne, Australia
Answered by: Barbara Medford

QUESTION:

I have an agave attenuata in a pot. It has been attacked by scales. I have been spraying it every 3-4 days at night with a chemical sold to me by the local gardening store. It's not helping and I am worried that the scales will take over the entire plant and kill it. At the moment, the only unaffected parts are in the middle and not yet opened out into leaves. I am wondering if the next step is to cut off the affected leaves? I have read your page on pruning agaves so I am prepared if that is the next step.

ANSWER:

We were just going to mention that Agave attenuata is native to Mexico, not to North America, which is our ordinary range of expertise, when we noticed you were writing us from Melbourne, Australia. It's not native there, either. We don't know what your climactic conditions are, or your normal temperatures, but we will try to find some literature that will perhaps help.

Begin by reading this article from the University of Arizona Cooperative Extension on Problems and Pests of Agave, Aloe, Cactus and Yucca. You will have to scroll down to Page 6 "Fungal diseases of leaves and pads," and then to Pages 9 and 10, "Coccineal scale, coccide scale, soft scale."

Next, take a look at this University of California Integrated Pest Management website on managing pests of the agave family (agaves and yuccas). Clicking on "Armored scales" on the right-hand side of that page will take you to a page to help you identify and then manage the scale you are experiencing. This article emphasizes that you need to know which scale you are dealing with in order to choose the proper control. Possible controls are discussed, and you should then be able to obtain a specific spray or oil for the appropriate treatment.

The article on diseases and pests of agaves is quite extensive, but you should read it all as it advises against the spraying of certain controls. It does not, however, recommend pruning. You would probably want to hold off on pruning and try to get the scales to go away, or at least become more manageable, then prune only heavily damaged leaves.