Thread-Footed (Tarsonemid) Mites

Adults of these three species of thread-footed mites (family Tarsonemidae) are 1/125 inch (0.2 mm) long or smaller; viewing them requires magnification of 20X to 40X. Their characteristic damage to crops is generally the basis for recognizing these pests are present and warrant management. The life stages of tarsonemids are egg, larva, nymph (or pseudopupa), and adult.

Eggs are oval and about 1/250 inch (0.1 mm) long. Larvae and nymphs are colorless to white and have three pairs of legs. Adult tarsonemids have four pairs of legs. They are named thread-footed mites for the long, thin appendage on the rear leg especially in males. Males use this to pick up and carry an immature female (nymph, or pseudopupa) on their back so they can mate as soon as she matures.

Cyclamen mite adults are oblong and pale yellowish brown. Adults and nymphs feed mostly enclosed in crevices of buds, tips of succulent terminals, and unfolding (immature) leaflets. Development is favored by temperatures ranging 60° to 80°F and high relative humidity (80 to 90%).

Broad mite is more stout (wider relative to its length) and smaller than cyclamen mite. Female broad mites are oblong to roundish and have a lengthwise, pale stripe along the back that is lacking in cyclamen mite. Broad mite eggs have rows of white, peglike protrusions on upper surface that are not present in the colorless cyclamen mite eggs. Broad mite can often be found on underside of old and young leaves, especially during humid conditions. Eggs generally are laid on the surface of plant parts such as in depressions. Cyclamen mite mostly feeds and oviposits within crevices or folds of plants' immature tissues. Both species can complete 1 generation in 1 to 3 weeks at typical growing-season temperatures.

Bulb scale mites closely resemble cyclamen mites; they are oval, colorless when young, and pale, translucent brown when mature. Bulb scale mites occur mostly in groups between the scales of bulbs and around the neck where the leaves and flower stems emerge from bulbs. The mites overwinter between bulb scales, then during the growing season feed on the emerging immature leaf and flower tissue. Bulb scale mites have several generations per year, completing 1 generation in about 7 weeks in the field during the growing season. Note that bulb scale mites are a different type of mite than bulb mites (Rhizoglyphus spp., Acaridae); bulb mites are larger species and visible to the naked eye.

Broad mite and cyclamen mite cause generally similar types of damage. Affected leaves become distinctly cupped, thickened, and undersized. Leaves grow unusually close together, having shortened internodes. Portions of leaves can be brown or yellow and necrotic. The actual culprit may be distinguished by the feeding sites as described above. Examine infested tissue under magnification to confirm the species based on their distinctly different eggs and adult females.

When cyclamen mite feeds on vegetative (e.g., leaf) or flower buds they may be killed or new growth can be dramatically stunted and distorted. Hosts include African violet, alstroemeria, alyssum, begonia, carnation, chrysanthemum, exacum, fuchsia, gerbera, impatiens, kalanchoe, larkspur, schefflera, and others.

Broad mite damage occurs more widely on leaves and flowers. It typically causes bronzing, distortion, and stunting of leaves and stems of herbaceous plants and sometimes pale flecking on petals. Hosts of broad mite include African violet, begonia, chrysanthemum, gerbera, impatiens, and zinnia.

Bulb scale mites infest bulbs of Amaryllis (Hippeastrum) and daffodil (Narcissus). Their feeding causes brownish, longitudinal streaks and sometimes horizontal cracks, notched edges, or both in leaves. Leaves and flowers become severely distorted and die prematurely. Cutting infested bulbs in cross-section reveals patches of brown, necrotic tissue from mite feeding. Basal and bulb rots (e.g., caused by Fusarium oxysporum) and bulb and stem nematodes (Ditylenchus spp.) also cause brownish discoloration in bulbs, but commonly in ring patterns following the circumference of bulb scales; browning from bulb mites is more blotchy and scattered.

Releasing predaceous mites, cultural practices especially heat treatment, excellent sanitation, and applying certain acaricides (miticides) can control these pests.

Neoseiulus spp. and other predaceous mites commonly prey on tarsonemid mites. These commercially available predators have been effectively released to greatly reduce damage by broad mite and cyclamen mite. For more information, see Biological Control and Natural Enemy Releases for Biological Control of Crop Pests.

Carefully inspect new plants and stock to ensure that they are free of infestation. Quarantine new plants in a separate growing area until tissue has grown for several weeks and any pests present or their damage become more apparent. Disinfest plants if they may be infested. Immersing stock in 110.3°F water for 30 minutes or holding plants at 100% relative humidity and 110.3°F for 1 hour can entirely eliminate thread-footed mites. For more information, see Pests Controlled by Heat Treatment of Plants in Nurseries.

Use excellent sanitation in growing areas. Consider roguing (discarding) infested older plants and those nearby. Disinfest or steam clean benches and containers (if heat tolerant), then treat (e.g., with heat) other plants in that production area that may also have become colonized by these mites. Thread-footed mites readily walk between plants and growing-area surfaces and can spread on moving air, on whiteflies (broad mite), and on contaminated propagation tools, water, and workers. Since broad mite and cyclamen mite also feed on a large variety of weed species, keep production areas free of weeds that can serve as mite hosts. Promptly remove and dispose of crop residue and weeds in covered containers.

Biological and cultural controls are organically acceptable management methods. The botanical neem oil, certain narrow-range oils (Organic JMS Stylet Oil), and sulfur dust or spray are organically acceptable.

Visually inspect hosts for damage symptoms characteristic of thread-footed mites as part of a weekly scouting program. On known hosts damage symptoms are generally the basis for taking control actions as the mites are microscopic and difficult to observe. Submit samples for diagnosis if the cause of damage is uncertain. For example with African violet damage from foliar nematodes and boron deficiency can resemble injury from thread-footed mites.

Rely primarily on cultural controls (e.g., excellent sanitation) and heat treatment. Predaceous mites can be released after treating infested plants with heat. Thread-footed mites are difficult to control with contact miticides in part because of the difficulty in getting good coverage on the underside of foliage and in protected plant parts where the mites feed.

Selected Products Registered for Greenhouse or Nursery Ornamentals
Most of these products are not for bulb scale mite.