What you can do to slow the suckers from the deep

What can you do to save plants from root aphids and mealybugs? The truth is, not much. (For descriptions of each, see sidebars.) The reason for this harsh truth is that once these destructive pests are discovered and your plants are infested, they’re pretty much unstoppable. Exactly what are these insect pests capable of? Short answer: a lot. Long answer: leaf yellowing, plant stunting, wilting, and under extreme conditions, even death. Damage is usually noticed when plants are infested with high populations. Root aphids and mealybugs tend to be less active (likely due to their restrictive habitat) than their aboveground counterparts. Root aphids and mealybugs can spread to other plants via draining water from containers, in growing medium debris, or on equipment. Furthermore, root aphids and mealybugs may infest adjacent plants by means of crawling through drainage holes of containers.

Which is why it’s important for growers to be proactive and practice these pest-management techniques:

Routinely inspect the root system of susceptible plants to detect early infestations of either root aphids or mealybugs. This will alleviate their spreading to other plants within the greenhouse. Sanitation is the primary means of avoiding future infestations of either insect pest. For example, once root aphids or mealybugs have been positively identified as causing the problem then all infested plants (and even those adjacent to infested plants) should be immediately discarded. Avoid carrying-over stock plants or “pet plants,” which may harbor root aphids and mealybugs, and be a potential source of infestation. In addition, use only new containers; avoid reusing old containers.

Know your insecticides. The use of insecticides may be limited because the entire growing medium profile must be thoroughly soaked and the growing medium, depending on the percentage of bark and peat moss, may inhibit activity by binding to the active ingredient. Regulating populations of root aphids and mealybugs with either contact or systemic insecticides is extremely difficult because of the protective waxy coating present on the later stages, which inhibits direct contact with the insecticide. In addition, root aphids and mealybugs may hide under the root ball thus allowing them to escape exposure to any insecticide residues. Systemic insecticides may not be effective against root aphids and mealybugs as insufficient (non-lethal) concentrations of the active ingredient may not accumulate in the roots where they are feeding. There are several insecticides that are registered for use against root mealybugs in particularly including imidacloprid and dinotefuran; however, multiple applications will generally be required. Furthermore, a sufficient volume of water must be applied to ensure contact with either root aphids or mealybugs within the growing medium.

Consider partnering with a predator. A biological control agent that is commercially available and recommended for use against root mealybugs is the predatory rove beetle, Dalotia (=Atheta) coriaria, which also feeds on fungus gnat larvae.

However, it is important to initiate releases of D. coriaria early on in the production cycle. If you have questions concerning the use of this predator against root mealybugs consult with your biological control supplier or distributor for information regarding timing of applications and release rates.

Raymond A. Cloyd is professor and extension specialist in Horticultural Entomology/Integrated Pest Management at Kansas State University in Manhattan, KS.