Aphid Control in the Yard and Garden
 | Author:
Allison Kosto, MSU Broadwater County Extension Agent
MSU Broadwater County Extension Agent |
Aphid Control in the Yard and Garden
Allison Kosto
MSU Broadwater County Extension Agent
Aphids have long been a pest in the yard and garden. June is often their peak population. Later in the summer, populations naturally decline as the predator population increases. However, they can still cause severe damage and sometimes intervention is necessary.
Aphids are an issue for several reasons. They have sucking mouth parts that pierce the plant and suck out fluids. Over time, this can diminish plant health. Symptoms include wilting, leaf curling and dieback of shoots and buds. Aphids can also carry many viral diseases. Another problem related to aphids is their production of sticky honeydew. Honeydew is a waste material excreted by aphids. It can cover leaves, branches and even sidewalks. Sooty mold can grow on the honeydew, adding another problem for the plant.
There are thousands of aphid species worldwide, but only a small number are considered serious pests. Most aphid species are host specific, meaning they only feed on certain plants. Only a few species feed on multiple host plants. This is good news because it means that if you have aphids in your ash tree, for example, it is unlikely that this specific aphid will move to nearby plants or different tree species.
Many aphid species are green, but they can also be white, yellow, pink, brown, black or mottled. Most have a pattern but it’s often difficult to see. They are very small with pear-shaped bodies and a pair of pipe-like structures called cornicles protruding from the back of the body. Colonies consist of winged and wingless forms of aphids. A majority are wingless which remain and reproduce on the plant. The colony will produce winged aphids when it is getting overcrowded, or the plant is starting to decline.
The life cycle of aphids is unique. Male aphids are rare and only seen in late summer or early fall for the last generation. Female aphids give live birth to a genetically identical daughter through asexual reproduction. A newborn will be fully grown in 10 to 14 days. Adults produce three to five young per day over the course of their lifetime, which can be up to a month. At the end of the summer, both male and female aphids are produced and result in sexual reproduction that allows females to lay eggs. The eggs are laid around buds or on stems to allow them to overwinter.
Sometimes the first signs of aphids are not actually the aphid itself. You may notice other strange symptoms before observing an aphid. One telltale sign is a sudden invasion of ants. Ants along with bees and wasps are attracted to the honeydew secretion. Leaf curling, especially in trees, is also another sign.
The good news is that there are several control options. Famous natural enemies of aphids are ladybeetles and lacewings. While it is possible to purchase these biological control agents, they are most effective in a greenhouse where they stay in one location. Otherwise, they tend to disperse and may not be highly effective outdoors.
On shrubs and garden plants, aphids can often be managed by spraying them with water. The purpose is to injure the aphids and knock them off in hopes that they won’t return.
There are also a variety of chemical control options. Reduced risk or organic pesticide options include dormant season oils, insecticidal soap, horticultural oil and neem oil. These products primarily work by smothering the insect so good coverage is key. More than one application may be necessary. Pyrethrin is another natural pesticide. For a pesticide with longer residual, pyrethroid products or malathion are options. However, these pesticides can have serious effects on pollinators so should be used with caution and not when plants are in bloom.
Systemic insecticides are also an option. The most common active ingredient is imidacloprid. It comes in a spray or can be applied to the soil underneath the plant. The latter is a great option for large trees that are difficult to impossible to get good coverage with a spray. These pesticides will provide longer control, up to a couple of months. However, they can pose a risk to pollinators so should be used cautiously and applied after flowering.
For assistance identifying insect pests or control recommendations, contact MSU Extension in Broadwater County at 406-266-9242 or allison.kosto@montana.edu.
