Saturday, July 08, 2017 1:00 am
Curled leaves a sign of aphids
Question: The leaves on many perennials and landscape plants are curling. What's going on?
Answer: Insect pests are about three weeks behind schedule this season because of the unusually cool rainy spring we have experienced. We have received many samples at the extension office with these symptoms you describe.
This has been a banner year for our old friend the aphid. Aphids absolutely love cool springs, and so populations of aphids have built up quickly this year.
Aphids are soft-bodied insects with piercing, sucking mouthparts. The curling on the leaves is caused by the aphids feeding on the plant sap – literally sucking the very lifeblood of the plant. Think of aphids as small pale green vampires that don't like the full sun and light of the day. This is why one has to look on the underside of the leaves to find them hiding and lurking there.
Many aphids exude clear sticky honeydew that one sees on leaves, but the woolly aphids that are on plants like river birch exude a white woolly substance that sticks the leaf blades together and helps them hide from predators.
Aphids also “wiggle” their rear ends when disturbed – somewhat similar to the dances one sees honeybees exhibit when communicating the direction of a food source.
Aphids have an incomplete cycle of metamorphosis. This means that immature adults (I call them teenage aphids) hatch directly from eggs. The teenagers happen to be born pregnant and quickly molt and develop into winged adults, which lay eggs that hatch into – you guessed it – more pregnant females. It is easy to see how aphid populations explode when conditions are optimal.
Several strategies exist for aphid control. Earth-friendly contact insecticides such as insecticidal soap, pyrethrum, permethrin and neem can be used on perennials and smaller shrubs, taking special care to spray on the undersides of leaves.
Sprays and/or root drenches of imidacloprid (Bayer Advanced Tree and Shrub Insect Control, Fertilome Systemic Trees and Shrub Insect Control) or Orthene (Ortho Systemic Insect Control) will help control aphids on larger trees and shrubs. Try to avoid using systemic insecticides on plants that are flowering to avoid killing bees.
Large trees can be injected with a pesticide that controls aphids by an arborist. Keep in mind that aphids rarely will kill trees, but they can weaken them and make them more susceptible to other insect pests and diseases.
As the hot summer approaches, the aphid populations will decrease – replaced perhaps by some other pest, which prefers the dog days of summer over our cool rainy spring.
The Plant Medic, written by Ricky Kemery, appears every other Saturday. Kemery is the extension educator for horticulture at the Allen County branch of the Purdue Extension Service.