Aphids are soft-bodied, pear-shaped insects about 1/16 – 3/8 inch long. They are sucking insects that form colonies, often on tender plant tissue such as newly-opened leaves, where they cause curling. They are very prolific, especially when they lay live young instead of eggs. Under greenhouse conditions, all aphids are usually females that give birth to live offspring (3-6 per day). Young start feeding immediately, and may mature and be ready to reproduce in a week. There are over 400 species of aphids; common colors are green, pink, red, orange, yellow, black, brown, and gray. Aphids may be winged or wingless; new infestations are usually wingless. Besides weakening plant growth by sucking plant phloem, aphids secrete a sticky honeydew which can become black and moldy. Aphids are also responsible for the transmission of plant viruses
The key characteristic for distinguishing aphids from all other groups is their “tail pipes” or cornicles on the rear of the abdomen – all aphids have two there. It would be best to have an entomologist that is familiar with aphids identify the species, however, that is not often possible. The most common species found in the greenhouse are the green peach (Myzus persicae), melon or cotton (Aphis gossypii), potato (Macrosiphum euphorbiae), and chrysanthemum (Macrosiphoniella sanborni) aphids. To distinguish the green peach aphid (which varies in color from light green to rose) from the melon aphid, take a close look at the head. The green peach aphid has an indentation which looks (in the words of Dr. Jim Price of the Univ. of Fla.)like it “was struck between the antennae with a 2 x 4″.
Melon aphids may be yellow, green, dark green, or black. Potato aphids are large, long-legged pink or green aphids that form colonies which fall quickly off the plant when startled. Their head structure looks more similar to the melon aphid drawing. They can be differentiated from green or pink melon aphid by their large body size, their long thin cornicles (melon aphids’ are short and stubby). Black melon aphids automatically are differntiated by their color. Chrysanthemum aphids are not as common. They are shiny, dark red-brown to blackish-brown, and their colonies often line up uniformly along stems.
Aphids are serious greenhouse pests mainly because they reproduce so rapidly. Control aphids first by limiting introductions from outside the greenhouse. Screen entrances, inspect plant introductions for aphids, remove weeds that may harbor aphids, and dispose of plant debris promptly. Avoid over-fertilizing with nitrogen, and control ants that may protect aphids from predators.
Plants must be monitored frequently for the first sign of aphids – check growing tips and undersides of leaves. Yellow sticky cards are not useful for monitoring aphids, since only winged aphids are attracted to them. If winged aphids are found on sticky cards, they may be strays from outside, which may or may not be crop pests. Or, if they are the winged type of a common greenhouse aphid pest, this usually means that aphid colonies are crowded – and thus a serious aphid problem already exists, and it’s too late for biological control.
Physical or chemical controls
Syringing – knocking aphids off plants with a water spray – is a time-honored method of control. Aphids frequently become resistant to pesticides; using beneficial insects can delay development of resistance. Insecticidal soaps and summer horticultural oil (when not phytotoxic) are effective. Avoid using most residual insecticides for a period of three months prior to planned use of biological controls.
IPM Laboratories, Inc. warrants that the biological controls you receive will be alive and healthy when received and will contain the correct number of the species you ordered. However, as with any pest control measure, success cannot be guaranteed. IPM Laboratories, Inc. makes no guarantee, express or implied, as to the effectiveness of these products.
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