What's eating my sandy sulcorebutia?

Sandy Sulcorebutia (Sulcorebutia arenacea) is a tiny clustering cactus whose tight offsetting growth makes it especially prone to root mealybugs and mealybugs lodged between heads. Spider mites also occur. Annual unpotting to inspect roots is the best preventative — hidden root infestations cause the most serious decline.

Unexplained soft, shrivelled body despite normal watering; white powdery filaments on roots when removed from pot Unpot, rinse roots, dry for a few days; repot into fresh mineral grit mix; water with diluted neem solution; repeat drenches monthly

White wool between tightly packed clusters and in areoles; honeydew and sooty mould on the soil surface Carefully apply alcohol on a cotton swab between clusters; treat whole plant with neem oil spray; space clusters apart after repotting for better visibility

Faint webbing and pale mottling on stem skin in dry heated environments Rinse plant gently; apply insecticidal soap or neem oil spray; improve air circulation around the plant