Ive had this cactus which i think is a Pachycereus Schotti/Monstrosus since years and its been growing fabulous. Ive just recently noticed it acquired some brown scales (non Insect) and looks like theres something wrong. Could it be from some chemical reaction? I did spray some Neem oil on several plants around it?? I loved this cactus and would hate to see it die. Help! Thanks!