Spider Mites

• Of all the different types of plant-feeding mites, spider mites make up the largest group. These reddish-brown, eight-legged pests are part of the Tetranychidae family and are very hard to see because they are less than 1 millimeter in size. Spider mite eggs overwinter on the cactus and then hatch into tiny six-legged larvae. The spider mite larvae morph into two other stages where they grow two additional legs before finally becoming adult spider mites.
  
  

Damage

• Spider mites cause more damage to cacti than any other pest. Spider mite damage is often noticed before the actual pest is. They suck juice from the plant cells and spin fine webbing in between the cactus' stems, especially near the top. Brown, yellow or gray spots spread all over the cactus. As the juices are sucked out of the plant it becomes dehydrated and, if left unchecked, eventually dies.
  
  

Prevention

• Due to the miniscule size of spider mites,the damage is more noticeable than the actual pest. By the time the damage is noticeable, an infestation has often already occurred. Starting in late winter to early spring, spray the cactus with neem or horticultural oil to kill overwintering spider mite eggs. Check the tops of cacti plants for webbing and use a magnifying glass to spot the tiny mites. A slight increase in humidity also helps keep spider mites away, but it should be done with care. Lightly spray the stems with clean water once a week to add humidity, but don't saturate the cactus.
  
  

Control

• On other types of plants, rinsing the plant with water or spraying with a strong stream from a garden hose is effective at killing the pests. But most cacti are sensitive to moisture, so this is not a recommended method. Instead, wipe the stems down with rubbing alcohol. Insecticidal soap made with water, and a small amount of mild dish soap and neem oil kills spider mites. Spray the solution either early in the morning or in the evening to avoid direct sunlight. Chemical insecticides made for spider mites are also effective.