Mealybugs can destroy a Haworthia in months if left unattended. In addition, they often cause other severe complications like rot. Besides constant inspections, applying systemic insecticides periodically is an excellent preventative measure.
Surface mealybugs tend to hide in between leaves or where leaves attach to the stem. During the inspection, look for their white flecks or cottony residues. Root mealybugs dwell underground. It is recommended to regularly lift random plants out of containers and inspect the roots. Root mealybugs often leave white markings on the roots and the nearby growing medium.
For an infested plant, clean as much of the growing medium out of the roots, even this may tear off some roots. The growing medium removed should be discarded. Soak the whole plant in a warm 1% solution of potassium fatty acids (often branded as insecticidal soap) for 2~12 hours. This kills any adults and eggs. Rinse the plant in warm water and let it dry out in a cool and shaded place. After that, follow the rooting process to let the plant recover.
A systemic insecticide is absorbed by a plant, transported to all the tissues and remains active for a period of time (often in months). Imidacloprid is a very effective systemic insecticide against mealybugs. Apply it once every half a year at spring and autumn, when Haworthias are in their peak growth periods seasons and actively absorbing water. Use a 0.004% solution and water until the growing medium is fully drenched.