Question
I have recently discovered that my Yucca, which is quite mature, has been infested with scale bugs.  The plant has been in the same pot for some time now and positioning has not been changed recently, where could the scale have come from?  I have sprayed it down with insecticide and then rinsed with water and repeated...Is this all that can be done, or have you any other suggestions?  Also what is the likelihood the scale infesting any of my other house plants, I have many, close to eachother?  How long should I keep the Yucca alienated from the others?  I hope this is specific enough, I really appreciate you taking the time to help out.  

Answer
Hi Caroline,

First, lets be sure that your Yucca really had scale. Yuccas often develop brown spots that are sometimes mistaken for scale. Scale scratches off easily with your fingernail. Scale also leaves a tell-tale sticky substance behind.

Assuming your Yucca does have scale, it is impossible to know exactly where it cam from. Usually a pest-infesed plant had the pest in very small numbers at the time of purchase. The critters can go unnoticed for years until conditions are favorable for their rapid reproduction. Then they suddenly become noticeable and appear to have come out of nowhere. It is also possible that the Yucca picked up the scale from one of your other plants.

Not all insecticides are effective against scale. What did you use? Rinsing after spraying defeats the residual effects that the insecticide has. There are safe, non-toxic treatments for scale, as well. If you have used the wrong insecticide, I will give you better treatment instructions.

Scale can spread, but it does so slowly and it spreads only to favored host species. To be on the safe side, check all of your plants carefully, especially those that were closest to the Yucca. Once your Yucca has been treated properly, then it is no longer at risk to your other plants and quarantine is not necesasary.

Please let me know if any of this is unclear or if you have any additional questions.

Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

You can E-mail me directly at: [email protected]

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