Monday, February 25, 2013

Common Houseplant Pests Part 3 - Scale

Here's an Agave plant. Notice anything?

Take a closer look!

Brown fleck in red circle.
Here it is on a Yucca plant. And it's not damage or part of the plant.

What I've taking photos of are tiny insects called scale. Here they are feeding both on an Agave and Yucca leaves. There are several species of scale. Scale are sap sucking, flat discs - moving ever so slow, and multiplying under the radar. These insects go undetected until their numbers are high, unless you know what to look for.

I hate using chemicals. I avoid using them as much as possible. Unfortunately, with this practice, patience and perseverance are key and constant monitoring over a period of time is necessary to get rid of them.

This agave plant is young.  It's newly emerging leaves are also targeted by scale more so than then older leaves. The tender tissue of new leaves are more delectable for the scale to feed on. Easier for their mouth parts to tap into.

You may wonder where they come from. Sometimes they go unnoticed when you make the plant purchase or receive one as gifts. Scale eggs are laid in the "crotches" and crevasses of the base of the leaves. Adult lay them in protected areas. Once they hatch, juvenile in-star scale insects emerge. They migrate above their nested area and begin feeding. More often than not, you find greater numbers of scale insects towards the protected areas within the core of the plant. I consider them to be "lice" of the plant world. Real bother and difficult to get rid of.

Ever notice shiny, sticky leaves on your house plants and wonder, where did that come from? With scale and other sap sucking insects, you can detect their numbers by their excrement. They "poop" out honey-dew, the sappy remnants of their diet and it rains down on the foliage below. This poop is quite sticky and it makes the foliage shiny.

Be vigilant, by either gently scraping off the scale with your finger nails, or using a cloth or cotton swab (dampened by rubbing alcohol). If you find scale numbers too high to combat them individually, you can take a water bottle sprayer, and mix 1 part dish detergent, 1 part rubbing alcohol to 10 parts water. Agitate the spray mixture thoroughly. Spray the plant liberally, until all leaves, crevasses and crotches are soaked. After an hour or so, once the spray mixture has dried, take a dampened cloth with rubbing alcohol and wipe off the dead scale. This is important, as adult scale can have young eggs or newly hatched in-star scale marauding under their shells.  Repeat as necessary.  If you have a large house plant, and find it most difficult to spray, reduce it's size by pruning the plant. Less foliage means less chance for the insect to feed from. Reducing the bulk of the plant will eradicate many more insects than just spraying alone. If it cannot be pruned, wait to treat the plant until you can bring it outdoors. Treat then outside, where space and temperatures are more favourable.

In one experience, I had to repeat this process 4 times before I got rid of the insect for good.

Diligence pays off. It also becomes a learning process and a great tool in learning how the scale life-cycles persist. When it comes to plants, I'll give it my all to rid them of this pest.

Keep a close eye on your plants and it'll pay off.

This particular scale I've found on Yuccas, Dracaenas, Agave, Bromeliads and Sanseverias.


  1. thank you thank you thank you! ive been searching for half an hour to find out about this aloe scale bug that you identified for me! i finally came across your site and figured it out. thanks for the pictures and advice. your page will be in my book marks now! thank you!

    1. Yay! My pleasure! More info to come. Thanks for stopping by! ~ Heidi

    2. Thank you thank you thank you. I also had this problem. I have a huge agave plant that I’ve been taking care of and just noticed hundreds of these on my guava plant it broke my heart

  2. what kind of agave is this?? genus..species?

    1. To be honest, I have no idea. We got a baby from a friend. It's a dwarf for sure - with slight variegation on it's edges. I should do a post on how well it's growing since the scale is gone.

  3. If the plant is beyond saving, can I reuse the soil for a new plant? Or will the scales come back because they are in the soil?

    1. Yes, scale certainly can come back. You never know what dead female may have dropped into the soil with live eggs in toe. I would discard. Clean your pots thoroughly too.


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