White patches on pads

[Terse]

I got this from Homebase on the 25th of June. The pot just said opuntia with the name of the pot, I think it’s Opuntia microdasys. It lives by my bedroom window which is south facing. I gave it a tiny bit of rainwater when I got it since I didn’t know when last it had been watered and I planned to water it next week. I’ve noticed white patches on the pads and they are starting to look bad. Does anyone know what’s going on? I’m quite new to this.













Have I messed up already?

[jerrytheplater]

Looks like Mealy Bugs. I know a 2% soap solution will kill them. Insecticidal soap is sold in our stores over here. Same stuff. You may have to respray weekly for a while.

[Minnesota]

I tend to agree with Jerry's assessment: the appearance of the white, fuzzy, powdery spots looks like mealies. I was given an Opuntia microdasys six months ago with these, and it took multiple weeks of spraying with an insecticide with isolation to eradicate them. You might want to unpot to check the lower stem and roots before you begin spraying to know the extent of what you're dealing with. If it is mealy bug, even when you don't see them anymore is not a reason to believe they are eradicated; maintain your course until you are certain these critters are gone. They are highly communicable to other plants in sizes not noticeable.

Best of luck,

Bret

[Steve Johnson]

Hello Terse,

You may have the beginnings of a mealybug infestation, although hard to tell at the moment. Even if you do, that's not your biggest problem, so you'll need to contend with the following:

• A comment and recommendation I recently made for a new member in Germany should be helpful to you as well:

  • For good or ill, everythings starts out in the roots. It appears that you're growing the Opuntia in potting soil -- too heavy and rich in organic materials for growing desert cacti. I highly recommend that you lean out the soil by mixing it with mineral gravel. IMO horticultural pumice is best, although I don't think you can find it. From Amazon Germany, try this instead:
    
    https://www.amazon.de/HanseGrand-Expand ... 9hdGY&th=1
    
    My default recommendation is a mix of 50% soil and 50% mineral gravel. This will improve drainage with better aeration for cactus roots to grow in. Better root growth = healthier stem growth.

  For the mineral component, check out your choices on Amazon UK:
  
  https://www.amazon.co.uk/s?k=pumice+for ... _sb_noss_1
  
  You'll have to unpot the plant, clean the soil out of the roots as thoroughly as possible, and repot in fresh dry mix. Caution! The bundles of teeny-tiny spines on Opuntias are called glochids. They'll stick into the skin like nobody's business, so don't handle yours with bare hands -- use thick gardening gloves or tongs instead. If you lose some roots in the unpotting process, don't worry, your Opuntia will grow more roots. Once you repot it, let it settle in for 2 weeks and water it deeply every 2 weeks until the cactus growing season is over. Unlike many other desert species that should be kept dry in fall and winter, Opuntias do enjoy some occasional watering while they're dormant.

• The new pads are all stretched out and "leggy" -- this is called etiolation, which is caused by inadequate light. I grew up in the "olden times" when fluorescent and incandescent lights were all we had, so trying to grow cacti indoors was at best difficult. However, LED lighting technology is a genuine game-changer, and you'll find plenty of choices on Amazon:
  
  https://www.amazon.co.uk/s?k=grow+light ... nb_sb_noss

If you'd like to start building an indoor cactus collection, a good grow light setup will do the trick.