The tomato russet mite (Aculops lycopersici) is a minuscule pest, often less than 0.2 millimeters long, making early detection challenging. Despite their tiny size, these mites can cause significant damage and yield losses to tomato plants and other nightshade family members if infestations are left unchecked.
Identifying a Tomato Russet Mite Infestation
Identifying a tomato russet mite infestation relies on observing distinct symptoms, as the mites are nearly invisible without magnification. Initial signs appear on lower leaves, which may yellow, droop, or show a slightly greasy appearance. As the infestation advances, “russeting” develops, turning stems and leaves bronze, tan, or rusty, starting from the plant’s base and moving upwards.
Affected parts may feel rough or sandpapery, and stems can become brittle. Leaves may curl inwards, shrivel, and lead to defoliation. A 10x or 20x hand lens is required to confirm the presence of these tiny, wedge-shaped, yellowish mites on the plant surface. While tomatoes are their primary host, these mites also infest other nightshade plants like potatoes, peppers, and eggplants, exhibiting similar symptoms.
Control and Management Strategies
Managing an active tomato russet mite infestation requires prompt and thorough control. For organic or low-impact solutions, wettable sulfur is a recommended treatment, effective when applied to all plant surfaces, including undersides of leaves and stems. Use sulfur with caution when temperatures exceed 90°F (32°C) to avoid plant damage. Horticultural oils and insecticidal soaps can also suppress mite populations by smothering them, requiring repeat applications every 5-7 days for several weeks to target successive generations.
Another approach involves introducing predatory mites, such as Amblyseius swirskii or Neoseiulus californicus, which feed on tomato russet mites. These beneficial mites are effective in enclosed environments like greenhouses or high tunnels. For severe infestations, chemical miticides labeled for russet mites on edible plants are available. When using chemical treatments, carefully read product labels, adhere to application rates, and observe pre-harvest intervals for safety.
Preventing Future Outbreaks
Preventing future tomato russet mite outbreaks centers on good garden hygiene and proactive management practices. At the end of the growing season, remove and destroy all tomato plant debris, especially any that showed signs of infestation, to eliminate overwintering sites for the mites. This includes disposing of affected plants rather than composting them, as mites can survive in plant residue.
Practicing crop rotation is also beneficial; planting tomatoes or other nightshade crops in a different garden location each year helps break the mite’s life cycle in the soil. Controlling weeds, particularly those in the nightshade family like black nightshade or hairy nightshade, is important because they can serve as alternative host plants. Finally, carefully inspecting any new tomato seedlings or transplants before introducing them into the garden can prevent inadvertently introducing mites from an outside source.