Garden lice, another term for the insect pest called aphids, infest irises. Keeping your irises as healthy and vigorous as possible is key to creating the most ideal environment for resisting or dealing with aphids. Garden lice can lead to diminished health of the entire iris plant and other problems like petal damage.
Garden lice come in a variety of colors but generally show up as green or black. They are 1/10 inch long and due to their small size they can be hard to see and even harder to identify. However, all garden lice display small tube-like formations on their backs.
All aphids, no matter the species, feed on plant parts in clustered groups. With a preference for less established leaves and shoots, garden lice feed on indoor and outdoor plants including vegetables, crops, fruiting plants and ornamental plants. Garden lice feed on plant juices by injecting their mouths into plant tissues, according to the Virginia Cooperative Extension.
Garden lice damage irises both by parasitically removing the plants' natural fluids and by transferring diseases through feeding. Additionally, the feeding process causes the excretion of honeydew (a sugary substance) that leaves irises more susceptible to fungal infections that thrive in the sweet, moist conditions. Damage includes stunted growth of all plant parts, diminished health, leaf curl, visible honeydew and decreased photosynthesis capabilities, according to the Virginia Cooperative Extension.
The lice lay eggs in cold weather that don't hatch until spring. So insecticidal soap or horticultural oil should be applied during the winter when the aphids and the eggs are present. Spray until the entire plant is covered. Reapply if aphids reappear and contact an extension agent or pest professional if the infestation does not subside after several soap/oil applications. Chemical controls should only be used when necessary to avoid damage to plant tissue.
Always keep your plant as vigorous as possible through proper care such as exposure to full sunlight and growth in moist, well-drained soil. "Natural enemies" like parasitic wasps, flower fly maggots, lady beetles and lacewings can also control the lice, according to the Virginia Cooperative Extension. These "beneficial" insects can be purchased through garden catalogs or online gardening sources and a single package of them will usually suffice. There is no risk of introducing these natural enemies as they are considered friends to a garden and a natural part of an ecosystem.