Question about an ill cactus (scale?)

Trouble shoot problems you are having with your cactus.
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t_fern
Posts: 1
Joined: Mon May 23, 2022 9:17 pm

Question about an ill cactus (scale?)

Post by t_fern »

Hi all,

I have a cactus growing in a pot outside my house that is having some trouble; it seems like it has a scale problem, although I am unable to see the insects when I examine it closely, just the scales. I've been trying to scrape off the scale and using a copper pesticide recommended by my local garden store, although it's not clear that it's doing much. Most notably, the cactus has been ejecting a white substance from itself, see photos below, that I haven't seen anywhere online. I'm curious: Is there more I can do to fight the scale? And what is that white stuff—does it mean the cactus is past the point of no return?
cactus-1.jpeg
cactus-1.jpeg (74.63 KiB) Viewed 665 times
cactus-2.jpeg
cactus-2.jpeg (66.72 KiB) Viewed 665 times

Any advice or perspective is much appreciated!

thank you,

Tim
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Steve Johnson
Posts: 4514
Joined: Thu Nov 03, 2011 4:44 am
Location: Los Angeles, CA (Zone 10b)

Re: Question about an ill cactus (scale?)

Post by Steve Johnson »

First of all, see this:

https://www.cactiguide.com/forum/viewtopic.php?t=43819

This might help:

https://www.cactiguide.com/cactipests/#scale

From the Morton Arboretum website (https://mortonarb.org/plant-and-protect ... e-insects/):

"There are many species of scale insects that feed on a wide range of host plants. Scale insects are a unique group, that look quite different from other insects. In their juvenile growth stage, they are referred to as “crawlers.” As crawlers, they are highly mobile, six-legged, have no protective cover, and are usually smaller than a pinhead. However, at maturity, scale insects are immobile, have no visible legs or antennae, and in the case of armored scales, are covered with a protective shell that ranges from about 1/16-to-3/8-inches in size."
If you just want photos without all the blather, please visit my Flickr gallery.
My location: Los Angeles, CA (Zone 10b)
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PolishGuy
Posts: 17
Joined: Tue May 24, 2022 11:02 pm
Location: Poland, dolnośląskie (lower silesia)

Re: Question about an ill cactus (scale?)

Post by PolishGuy »

The orange blotchy discoloration/spots arround the scales could also be some fungal/bacterial infections like rust (but I cant say with 100% confidence) that probably got there from physical damage from the scales.

Its probably best to treat plant both for scales and fungal infections with some systemic insecticides and systemic fungicides, you would need to either buy one product that is already formulated with 2 or 3 ingredients together or check if the insecticide and fungicide of your choice can be mixed together.

You could also treat the plant with one thing and then wait recommended amount of time to apply the other thing but then you risk scales or infection spreading while the other thing is being cured.

When it comes to what exact chemicals you should use I sadly can't give you soild help as I dont know what would really work for scales but I will try to tell you what I know:

I know that Imidacloprid works well as soil drench for mealybugs but short googling tells me its not the best for scales.
For fungal infection if its rust you could try to spray it with trifloxystrobin and/or tebuconazole (Ive seen products containing both together) as I've heard they should work well for that and trifloxystrobin alone helped me cure my cactus from rust.

Again I have no idea if trifloxystrobin and tebuconazole can be mixed with insecticides like imidaclorpid so you need to ask someone more knowledgeable.

Also whatever you decide to use wear protective clothing, gloves and facemask with some filters as systemic fungicides and insecticides are toxic and very dangerous
Poland, dolnośląskie (lower silesia)
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