We get lots of questions around here, some with photos, some with shocking photos. This question first came to us over the phone, and so I asked for a photo…
Please tell me what u think this disease is!
Sent from my Verizon Wireless BlackBerry
Here’s the photo…
And the answer is…
That’s scale. A lot of scale, on your Pachycereus marginatus. The plant might be able to be saved, but it will be permanently scarred. Spray it down with rubbing alcohol to kill the buggers and break through their shells and then carefully wipe them all away with a soft paint brush. Then spray the cactus down with neem oil and drench the soil with neem, and reapply a few more times. In March you should repot it into clean soil, and spray the roots completely too with the neem.