[Arid_gardener] prickly pear with cochineal scale

[Janet Howe]

Original message:

Anne
85015
anniebndan at earthlink.net

Prickly pear, about 11 years old, very healthy, developed something that
looks like cottage cheese all over the pads.  It has spread quickly and
the cactus now appears to be dying.  What could this be and how to
treat? Thank you.


Answer:

Anne, what you are describing on your prickly pear is called cochineal
scale.  The white cottage cheese appearing substance is actually a
coating a small insect creates as protection.  It's not unusual to find
this on prickly pear.  I have several different types of prickly pear,
some that seem to be magnets for the scale, while others tend to not be
bothered.  

In case you're interested, Native Americans use(d) cochineal scale as a
red dye.  If the white substance is pressed on (I don't recommend using
your finger!) a very brilliant red substance is produced. It makes a
fine dye, but a large infestation will eventually harm the plant, as
you've discovered -- I try and keep my cactus relatively free of the
substance.  

The good new is that if you're plant isn't too far gone, it is
treatable.  The best way to treat that I've found is to spray the plant
with soapy water, then follow with a blast of spray from a garden hose.
Mix soapy water mixture at a ratio of 1 gallon of water to 1 tablespoon
of soap (I've found liquid Ivory to work great).  Place in a spray
bottle and spray the entire plant thoroughly.  You'll notice as you
spray that the white, cottage cheese-like matter begins to dissolve and
you'll actually be able to see the little black insect beneath.  Once
I've sprayed the entire plant thoroughly (concentrate on the undersides
of the pads, and where the pads attach), I wait 10-15 minutes, then
follow up with a good blast of spray from the garden hose.  This will
knock off most of the scale.  

I've found that I need to keep a close eye out, and repeat as often as
necessary to keep the scale under control.  Good luck with your cactus!

Janet Howe
Master Gardener volunteer
University of Arizona Cooperative Extension