Broad mites are among the most destructive and difficult-to-detect pests facing agricultural and horticultural growers globally. These organisms are microscopic, making them virtually invisible to the naked eye, which allows infestations to become severe before they are noticed. They are highly polyphagous, meaning they feed on hundreds of different plant species across more than 60 families, causing significant economic damage. Since the pest is hard to spot, growers must rely entirely on recognizing the severe damage they cause to susceptible plants.
Identification and Biology
The broad mite, scientifically known as Polyphagotarsonemus latus, is classified as a tarsonemid mite, belonging to a family of mites distinct from common spider mites. Adult female broad mites are minute, measuring only about 0.2 to 0.25 millimeters long, oval in shape, and typically appear translucent or pale yellow to amber. The males are even smaller, and females can be differentiated by a faint, light stripe running down their backs.
A definitive characteristic is the egg, which is relatively large compared to the adult female. The eggs are elliptical and translucent, covered with approximately 30 to 37 scattered, whitish, dot-like bumps, giving them a distinct, jeweled appearance under magnification. The mite progresses through four life stages: egg, six-legged larva, a quiescent nymphal stage, and the eight-legged adult.
The speed of the broad mite life cycle is a primary reason for its destructive potential; a new generation can be produced in less than a week under optimal conditions. At warm temperatures between 70°F and 80°F, development from egg to adult takes only five to seven days. This rapid generation time allows populations to explode quickly, and the mites prefer to aggregate and feed on the newest, most tender growth near the plant’s terminal buds. Male mites play a role in dispersal, using their enlarged hind legs to pick up the female nymphs and carry them to fresh, uninfested young leaves before the females emerge into adults.
Recognizing Infestation Symptoms
The damage caused by broad mites presents a serious diagnostic challenge because symptoms are easily mistaken for other plant health issues. Growers frequently misidentify broad mite damage as a viral infection, a nutrient deficiency, or even injury from herbicide exposure. This misdiagnosis often leads to ineffective treatments, allowing the mite population to continue its rapid growth.
Broad mites possess piercing-sucking mouthparts that allow them to feed on plant cells, injecting a toxic saliva that disrupts normal plant development. The most characteristic symptom is the stunting, twisting, and severe malformation of new leaves and the terminal growing points. The new leaves may appear thickened, brittle, or “strapped,” and the growing tips can become hard and distorted.
Damage on leaf surfaces often manifests as a dark, oily sheen or a distinctive “bronzing” or “russeting,” particularly on the undersides of new leaves. On fruiting plants, feeding can cause scabby or corky patches on the surface of developing fruit, leading to cracks and reduced market value. If flower buds are attacked, they may become distorted and eventually abort, halting the plant’s reproductive cycle.
Effective Management and Control
Managing a broad mite infestation requires an integrated pest management (IPM) strategy that combines sanitation, cultural practices, and targeted treatments. Since broad mites prefer to hide in protected areas like terminal buds and new growth, successful chemical control is difficult because many contact sprays cannot reach them. Immediately removing and destroying all heavily infested plants is a necessary first step in any control plan.
Sanitation is a primary defense, which includes inspecting and quarantining all new plant material before introduction. Weeds, especially broadleaf varieties, should be destroyed both within and around the growing area, as they serve as reservoirs for the mites during off-seasons. For high-value, small potted plants, a non-chemical option involves immersing the entire plant in water maintained at 115°F for 15 minutes, though this must be tested for plant tolerance.
Chemical control often relies on miticides with translaminar properties, meaning the active ingredient penetrates the leaf tissue to reach mites feeding inside or on the underside. The rapid life cycle of the broad mite necessitates the rotation of miticides from different chemical classes to prevent the development of pesticide resistance. Sulfur-based products are sometimes used, but growers must be cautious because sulfur can cause phytotoxicity on certain plant varieties, especially at high temperatures.
Biological control provides a sustainable long-term solution, particularly in controlled environments like greenhouses. Preventative releases of predatory mites, such as Neoseiulus cucumeris, Neoseiulus californicus, or Amblyseius swirskii, help suppress broad mite populations before they become established. These beneficial mites must be introduced early in the crop cycle to be effective, as they cannot control a severe, established infestation on their own.