Aphids
Several species of aphids are troublesome pests of greenhouse crops, orchards, gardens and indoor plantscapes. Green peach aphid (Myzus persicae) is common in greenhouses, while melon aphid (Aphis gossypii), potato aphid (Macrosiphum euphorbiae), and others also occur.
Myzus persicae, Aphis gossypii, and Macrosiphum euphorbiae
BIOLOGICAL CONTROL: Aphidius spp., Aphidoletes aphidimyza, Hippodamia convergens, Chrysoperla spp. (Lacewings), Aphelinus abdominalis, Azaguard, NoFly
OVERVIEW: Several species of aphids are troublesome pests of greenhouse crops, orchards, gardens and indoor plantscapes. Green peach aphid (Myzus persicae) is common in greenhouses, while melon aphid (Aphis gossypii), potato aphid (Macrosiphum euphorbiae), and others also occur.
DAMAGE: Aphids suck plant sap which causes distortion of enlarging leaves and shoots, and reduces the vigor of plants. As they feed, aphids produce sticky honeydew which drips onto leaves and fruit below. The honeydew is colonized by sooty molds, which reduces the quality of greenhouse vegetables and ornamentals. Some species of aphids also transmit plant viruses.
DESCRIPTION: Aphids are soft-bodied, pear-shaped insects about 1/16 - 1/18 in. long. Most are wingless, but some do have wings, which are transparent and held roof-like over their backs. Immature aphids look like smaller versions of wingless adults. Aphids generally develop in crowded colonies on the undersides of leaves and along stems. They occur most often in the oldest (lowest) leaves, and on the young shoots of plants.
LIFE CYCLE: Aphids reproduce very quickly because for most of the year, the colony is entirely made up of females. During the growing season, aphids continuously give birth to live young, without mating.On outdoor plants in the fall (due to short day-length), male aphids develop in colonies and mate with females, which produce eggs. The eggs will overwinter and hatch in the spring. In greenhouses, aphids may continue to reproduce all winter without laying eggs. Winged aphids develop when aphid colonies become crowded. These fly to new plants and can be transported long distances in air currents to quickly infest a crop.
MONITORING TIPS: Use a 10-15x hand lens to inspect plants weekly for developing aphid colonies. They are first found on the older, lower leaves; moving up to new growth later. Honeydew on leaves is a sign of aphids (or other sucking insects) on the leaves above. In greenhouses with poly floors, the floors will also become sticky with honeydew. Use yellow sticky traps at a rate of 1 card per 500-1,000 square feet to trap winged aphids. Traps can help identify when the winged aphids are present outdoors as well as where they may be entering greenhouses.
Weekly plant inspections instead of traps should be used to locate infestations inside greenhouses. By the time winged aphids are produced from colonies inside of a greenhouse, overcrowded aphid colonies are already present on plants.
BIOLOGICAL CONTROL: Several biological controls are available for control of aphids. They differ in their effectiveness at certain times of the year or at various levels of aphid populations. Aphids reproduce so quickly that it is often advisable to use two or more biological controls together to suppress the aphid population. It may be necessary to control ants in greenhouses, conservatories, and around outdoor trees because they can protect aphid colonies by removing predators.
Aphidius species (A. matricariae, A. colemani, A. ervi): Aphidius spp. are a group of parasitic wasps that parasitize many common species of aphids in greenhouses and outdoor crops. It is efficient at finding aphids and is most effective when applied preventatively before aphids are detected or when aphid populations are very low. Aphidius alone will not provide control when populations are high. During spring and summer, aphid populations grow too fast to be controlled by the parasite alone, therefore should be used with other aphid predators such as Aphidoletes. Aphidius does not diapause in response to short days, so it can be used year-round. Effectiveness may be reduced in late summer when Aphidius itself may be attacked by naturally occurring hyperparasitic wasps. For more information, see the Aphidius species technical sheet.
Aphidoletes aphidimyza: Aphidoletes larvae are predators of over 60 species of aphids and can be used on both indoor and outdoor plants. It is efficient at finding aphid colonies and effective against low and high populations. Aphidoletes diapause in short day conditions, unless supplemental lighting is used. Read the Aphidoletes aphidimyza technical sheet for more information.
Ladybugs: Both adult and larval ladybugs feed on a variety of aphid species. It is effective against high aphid populations, however field collected ladybugs enter diapause and are not effective indoors in winter months. Ladybugs will not survive in the absence of prey, therefore should be released after aphids are detected. For more information, please see the ladybug (Hippodamia convergens) technical sheet.
Lacewings (Chrysoperla spp.): The larvae of lacewings are predators of aphids and other soft-bodied insects, including other beneficial insects and even cannibalize their own species. Lacewings do not reproduce well in most greenhouse situations, therefore the eggs and larvae are generally used as a one-time control, rather than the expectation they will become established.
Aphelinus abdominalis: Aphelinus abdominalis is a parasitic wasp that target second and third instar aphids. Larger aphids are less frequently attacked, while the small aphids are also a food source for adults. Aphelinus will help prevent outbreaks of aphids when used as recommended. It may entirely prevent colonies developing if used at the beginning of the risk period. It may also be used at higher rates to bring moderate infestations under control, but should be used in conjunction with other biocontrols in this situation.
Azaguard: Provides control of more than 300 insect species. Please see the technical sheet below for information about rates and usage concerning spcific target pest. AzaGuard is a 3% Azadirachtin formulated Insect Growth Regulator (IGR) that offers broad spectrum insecticidal control on over 300 insect species. AzaGuard prevents molting between larval, pupal and nymphal stages and also repels insects in treated areas, reducing insect infestations in and around the facility.
NoFly: This aggressive fungus is a natural predator to select insect pests while non-pathogenic to beneficials. NoFly WP is also compatible with many chemicals making it an excellent tool for use in an integrated pest management (IPM) program. NoFly WP is effective against whiteflies, aphids, thrip and mealy bugs.
CHEMICAL CONTROLS: Insecticidal soap can be used as a clean-up for aphids before releasing biological controls, as it has no residual effect. It can be used in aphid hot spots without harming pupal stages of Aphidius and ladybugs, but it will affect other stages. Nicotine fumigant (PlantFume®) can also be used before release of biological controls as it has a 1-day residual effect. Pirimicarb (e.g. Pirliss®) can be used to reduce aphid numbers in hot spots without harming the pupal stage of Aphidius. It is also only slightly toxic to Aphidoletes, but the repellent effect of the pesticide disperses the aphids. It also has been found to repel Aphidoletes females from laying eggs on leaves with Pirimicarb residues, so avoid frequent use. Kinoprene (Enstar®) may be used in aphid hot spots without harming biological controls, but it is only registered for use on ornamentals.
OTHER MEASURES: In gardens and some indoor plants, wash high populations of aphids from plants with a strong spray of water before introducing biological controls. Keep the greenhouse weed-free before to remove alternate hosts for aphids, and maintain a 10 foot-wide weed-free border around the greenhouse. To prevent aphids entering greenhouses from outdoors, screen all entry points. Closely inspect all new plant material before bringing it into the greenhouse.
Source: Applied Bio-nomics Ltd.
