Spider mites
Almost invisible without a hand lens. Yellow-green to red-orange specks on the underside of the small serrated leaves, especially along the leaf-stem joints. Hot dry summer weather sends populations through the roof on stressed verbena.
Tiny pale dots tiny pale dots the upper leaf surface, then bronze patches that spread across the opposite-leaf pairs. Fine webbing strung between leaves and flower clusters in heavy infestations. Defoliates a stressed verbena in two to three weeks and stops the bloom show cold.
Shower the foliage with a hose every 3 days for 2 weeks
Hold a hose nozzle 12 inches from the plant and blast the underside of every leaf for 30 seconds. Mites can't reattach quickly when knocked off, and the moisture slows survivors. Verbena tolerates a hard rinse well. Repeat every 3 days for 2 weeks through the hot summer stretch.
Neem oil at dusk, every 5 days for 3 rounds
Mix 2 tablespoons cold-pressed neem oil and 1 teaspoon dish soap per gallon of water.
Spray the underside of every leaf and into the flower clusters at dusk to avoid burning the small petals.
Repeat every 5 days for 3 rounds. That covers the full egg-to-adult life cycle.
Water deeply at the base in summer
A verbena under drought stress is a verbena that gets defoliated. Deep-water at the soil line once or twice a week through summer instead of light frequent sprinkling. Stronger plants resist mite outbreaks because they keep leaf turgor up and stay less attractive to feeding.
