The broad mite, Polyphagotarsonemus latus, is a nearly microscopic pest that presents a significant challenge in crop and ornamental plant management. These mites are barely visible, with the adult female measuring only about 0.2 millimeters in length. Despite their tiny size, broad mites reproduce rapidly, completing their life cycle in as little as one week under ideal warm conditions. This fast turnover leads to quickly escalating populations that inject toxic saliva into the host plant, causing severe and lasting damage. The goal of eradication is to halt this cycle immediately, and this article provides targeted, practical methods for killing this problematic pest.
Identifying the Infestation and Vulnerable Life Stages
Broad mite feeding is primarily concentrated on the newest, actively growing tissues, such as the apical shoots, young leaves, and flower buds. The damage symptoms are often the first sign of an infestation, appearing as distorted, stunted, or bronzed new growth. Leaves may curl downward, become thickened, and develop a rough, corky texture, which can sometimes be mistaken for herbicide injury or a nutrient deficiency.
Confirmation requires a high-powered hand lens or microscope to inspect the undersides of the youngest leaves for the mites themselves or their distinctive eggs. The eggs are translucent and oval-shaped, covered in unique white, dot-like bumps that give them a jeweled appearance. Understanding the life cycle is crucial for effective control because the egg stage is highly resistant to most contact treatments.
The life cycle includes the egg, larva, quiescent nymph, and adult stages, with the entire process taking place quickly in warm, humid environments. Since eggs are often unaffected by a single application of miticide, successful eradication requires repeated treatments timed to kill the newly hatched larvae and adults before they can lay a new generation of eggs. Applications must be spaced approximately five to seven days apart over several weeks to break the reproductive cycle.
Targeted Chemical Control Options
Several chemical and non-synthetic products are effective at killing broad mites, but they require precise application and rotation to work correctly. Miticides with translaminar activity, such as those containing abamectin or spiromesifen, are often preferred because they penetrate the leaf tissue. This penetration creates a reservoir of the active ingredient inside the plant, allowing the chemical to reach mites feeding in the protected meristematic tissue of the growing tips.
For immediate knockdown of mobile stages, contact miticides like fenpyroximate or pyridaben can be highly effective. However, these products must thoroughly coat the mites to work, which is challenging since broad mites hide deep within the new growth. It is necessary to rotate between miticides with different Modes of Action (MOA) to prevent the mites from developing chemical resistance, a common problem due to their short generation time.
Horticultural oils and insecticidal soaps offer a less toxic option by smothering the mites upon direct contact. These products are highly effective against soft-bodied larvae and adults but generally have little impact on the hard-shelled eggs, necessitating multiple applications. Sulfur products are also effective miticides, but they must be used cautiously, as high temperatures can increase the risk of phytotoxicity, causing damage to the plants.
Implementing Biological Predators
Introducing natural enemies is a sustainable and long-term method for controlling broad mite populations, particularly in greenhouse or indoor environments. Specific predatory mites from the Phytoseiidae family are recognized for their ability to feed on and suppress broad mite numbers. The predatory mite Amblyseius swirskii is widely used and highly effective, often providing excellent control, especially when released preventatively.
Other effective species include Neoseiulus californicus and Neoseiulus cucumeris, which actively search out and consume the pest mites. These beneficial mites provide a better long-term solution than chemicals, as broad mites cannot develop resistance to being eaten. The success of a biological control program is dependent on the environmental conditions, with the predators requiring suitable temperature and humidity levels to establish and reproduce effectively.
Predator releases should ideally begin early in the crop cycle before mite populations become high, as they are better at prevention and maintenance than rapid eradication of a severe outbreak. For heavy infestations, a short-residual oil spray may be used first to reduce the broad mite population, followed by the introduction of the predatory mites to maintain control. The use of these biological controls can significantly reduce the reliance on chemical treatments over time.
Non-Chemical Environmental Treatments
Physical and environmental manipulation can eliminate broad mites without the use of chemical sprays or beneficial insects. One highly effective physical method is heat treatment, also known as thermotherapy, which is often used for small plants or plant cuttings. Broad mites and their eggs can be killed by submerging the infested plant material in hot water maintained at a temperature between 43°C and 49°C (109°F to 120°F) for approximately 15 minutes.
This method is attractive because it can kill all life stages, including the resistant eggs, in a single treatment, although the plant’s tolerance to the heat must be considered. Another simple cultural practice is the physical removal and disposal of heavily infested plant parts, such as severely distorted growing tips. This sanitation step immediately reduces the pest load and eliminates the areas where the mites are most concentrated.
Managing the growing environment can also suppress mite populations, as broad mites thrive in very high humidity. Increasing airflow and slightly lowering humidity can make the environment less favorable for the mites, slowing their reproductive rate. While environmental control is not typically a primary killing method, it is a crucial component of an integrated strategy that limits the severity of future outbreaks.