Weigela is a low-growing shrub that makes a snug defining garden border. Its flowers come in many shades, from white through pinks and purples. Guard your weigela from insect pests such as root nematodes, mealy bugs, Japanese beetles, and scale with these helpful tips.
These white grubs commonly affect weigela and other ornamental shrubbery. They bite into the plants' root structure and slowly kill the foliage and twigs. The leaves of the weigela turn reddish-yellow due to lack of nutrients when affected by root nematodes. As the infested roots die, the plant tries to send out more roots above the diseased ones, creating tangled root masses that cannot absorb water.
In hot weather, nematode infestation is more obvious as the plants try to survive the drought created by the root damage. Treat by adding leaf mold and other beneficial fungi to the soil. Adding a fish emulsion in liquid form will feed the weigela at the roots and repel or kill the root nematodes. If these are ineffective, treat the soil with a granular formula of ClandoSan, a nematode repellent. Apply it to fine channels sliced into the soil, avoiding the delicate feeder roots near the soil surface.
The weigela is often afflicted by these gray bugs, up to 1/3 inch long, with soft spines covered in a waxy white powder. Mealybugs chew on the weigela's leaves, draining their sap. They also attract ants, which feed on the honeydew the mealybugs secrete.
The weigela's leaves will take on a yellow tinge, and white filamented masses will appear on the leaves and stems of the shrub. Upon detecting mealybugs on your weigela shrub, spray the stems and leaves three times daily with neem insecticide. In the late winter months, coat the weigela twig bark with horticultural oil to prevent eggs laid by the insects from hatching in spring.
Four-Lined Plant Bugs
A common insect pest of weigela, the four-lined plant bug is small, yellow or green and round, with four broad black stripes down its back. It lays eggs in the stems connected to the newest leaf growth. Watch for leaf punctures that become large holes. Apply a soil insecticide, Imidacloprid, early in the growing season. As the larvae become nymphs, treat the weigela foliage with insecticidal soap, fine horticultural oil, or malathion.
Less commonly, the Japanese beetle will also eat the weigela's leaves, reducing its source of nutrition. Try to spot the beetles when the population is low, as insecticide will not be effective against large populations. Wash the shrubbery with water and spray with horticultural oil.
Three types of scale insects attack the weigela shrub: the barnacle, latania, and cottony cushion. Infestations appear as brown spots on the leaf tops. Predator bugs such as lacewing, pirate bugs and ladybugs are most effective against leaf scale bugs. Do not use insecticides as these will harm the predators. When the weigela is dormant in winter, apply horticultural oil to interrupt the life cycle of leaf scale bugs.