echinocereus engelmannii

Cause: Mealybugs are listed as the most common pest of cacti and succulents and settle on Echinocereus in the crown, between ribs and on the roots; they are small elliptical insects covered in a waxy white meal that lay their eggs within the white tufts clustered close to the body of the plant.

Solution: Bare the roots of the affected Echinocereus, wash every trace of old soil off the root ball, then dip the whole plant in a dilute malathion or systemic pesticide solution before repotting into fresh fast-draining cactus mix.

Prevention: Quarantine and inspect every new cactus, including its roots, before adding it to the collection, and sterilize the area around any infested plant because the waxy white meal shields mealybugs from many contact sprays.

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Cause: Scale insects are a distinct pest of Echinocereus and other cacti; unlike mealy bugs they are metallic grey and do not produce the typical white waxy meal, sitting flat against the cactus ribs and sucking sap until the surface is scarred and weakened, while exuding honeydew that can promote sooty mould.

Solution: Brush affected Echinocereus stems firmly with a soft brush so the dislodged scale insects cannot re-attach themselves and die where they fall, and apply a systemic insecticide recommended for scale because adult scales are almost impervious to most contact pesticides once they have settled.

Prevention: Inspect new Echinocereus plants and any quarantine neighbours regularly because scale insects barely move once they settle, and an attentive grower can catch a fresh infestation before it spreads across the whole cactus.

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Cause: Spider mites (red spider) are minute eight-legged arthropods, orange in colour and almost too small for the naked eye to see, that colonise the cactus and surround themselves with very fine webs while sucking sap from the plant body and causing disfigurement or reddening of the stem, thriving especially in hot and poorly ventilated conditions.

Solution: Apply a miticide or insecticidal soap and repeat treatments because one application is virtually never 100 per cent effective, and dust with sulphur as one of the oldest remedies for spider mite on cacti and succulents.

Prevention: Quarantine new plants and inspect them closely for fine webbing before adding them to the collection, and watch neighbouring plants upwind and downwind because spider mites disperse on the breeze and reappear as long as a reservoir of host plants remains nearby.

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