Answer: I'm assuming you have some type of prickly pear cactus with pads. Some of these actually turn purple in cold weather, such as the Santa Rita prickly pear. This is normal and no cause for concern. When you say it has white on it, I'm assuming you mean a white, cottony substance, that is kind of sticky if you touch it. The white is actually a protective coating manufactured by a very tiny scale insect called cochineal scale. The scale has been used for centuries to make a red dye. It is purposely cultivated and harvested on prickly pear in Mexico for this use. You can hose it off with a strong blast of water. It is hard to get it all since the scale is so small and can hide in the cactus nooks and crannies, so you may need to hose it periodically. The scale will do no great harm if hosed off periodically, so no other control is needed. If you have a lot of the scale on a plant, the water will actually run red when you spray it off!
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