Aphids are a common greenhouse pest of many greenhouse crops. Like thrips and whitefly, they cause damage to plants by piercing the leaves and sucking out the sap. Aphids are especially prevalent on the newer growth, causing curling and distortion of the leaves. In addition, they excrete a sugary sap, called honeydew, which drips on leaves below, along with their shed skins. Black sooty mold grows on the honeydew, adding to the unsightly appearance.
Aphids can also transmit viruses. Of primary concern is the cucumber mosaic virus, which can cause flower break and distortion on cyclamen, lisianthus and vinca.
Types Of Aphids
There are several types of aphids commonly seen on greenhouse crops. The most common is the green peach aphid, Myzus persicae. It is generally a light green color, sometimes tending to pinkish. The melon aphid (Aphis gossypii) is light yellow to dark green or even black in color, and the foxglove aphid (Aulacorthum solani) is light green and quite shiny. They can be identified with a hand lens by looking at the tube-like cornicles that protrude from the ends of their abdomens.
Aphids reproduce parthenogenetically, meaning they do not need to mate. All aphids are female, and they give birth to live nymphs, which are also female. They reproduce prolifically, with newborn nymphs reaching reproductive age in as few as seven days.
How To Monitor And Prevent Aphid Infestation
Regular monitoring by both visual inspection and with yellow sticky cards is vital to catch an infestation early. Melon aphids do not always have a winged stage and therefore may not be detected on sticky cards.
Systemic insecticides are often better than contact insecticides for control. Biological control methods include parasitic wasps, ladybugs, lacewings, predaceous midges and Beauveria bassiana, a fungus that kills insects.
Screening of greenhouse entrances is important, as are sanitation and weed control. Weeds can be a host for aphids in between crops.
Cañas, Luis. 2011. Aphids and Their Control. Ohio State University/OARDC. http://ohiofloriculture.osu.edu/sites/drupal-ohioflori.web/files/file/insect-update-aphids.pdf
Pundt, Leanne. 2000. Managing Aphids in the Greenhouse. University of Connecticut Integrated Pest Management. http://www.hort.uconn.edu/ipm/greenhs/htms/ghsaphid.htm
Sanderson, John P. Greenhouse Aphid Management. Cornell University Cooperative Extension. http://www.greenhouse.cornell.edu/pests/pdfs/insects/Aphids.pdf