Aphids Information
Species & Identification
Aphids are perhaps the most common pests in greenhouse operations. There are many different species of aphids, many of which specialized on certain plant families or species. In greenhouses, green peach and melon aphids are very common and can feed on many plant species. Foxglove aphids and potato aphid are also common in some greenhouses. Rose, chrysanthemum, and cabbage aphids are common pests on roses, mums, and ornamental kales, respectively.
Damage & Symptoms
Aphids use their needle- or straw-like mouthparts to suck plant sap from the vascular system. Plants infested with aphids may exhibit distorted new growth, stunting, and generally appear unhealthy. As aphids molt, white or silvery cast skins can be seen on leaf surfaces. Aphids deposit drops of honeydew after feeding, which make the cast skins stick to leaf surface and become more apparent. Honeydew promotes black sooty mold growth, which reduces plant quality.
Life Cycle
Aphids have a short life cycle and a high reproductive rate. An aphid’s life cycle is around 7 days. Newly hatched aphids may mature in 6 to 7 days. An adult female may produce 60 to 100 offspring in 20 to 30 days. In greenhouses, aphids commonly have up to 30 generations per year. When population levels are high enough, the population produces winged adults (called alates), which fly to other plants to start a new population. The high reproductive capability of aphids and a proclivity to develop insecticide resistance make aphids very problematic to control.
Scouting
Yellow sticky cards are a good tool for monitoring the presence and movement of winged adults. These cards should be placed near doors and near new plants. Additionally, randomly select 10 plants per 1,000 square feet of greenhouse space to thoroughly inspect for aphid presence. Check the underside of leaves and growing terminals for the aphids, cast skins, honeydew, and sooty mold.
Cultural Control
Place insect exclusion screens with fine mesh sizes (< 0.19 mm) in doorways and vents to prevent winged adults from entering the greenhouse. Excessive nitrogen fertilization has been shown to benefit the development and reproduction of aphids; therefore, avoid excessive fertilization.
Chemical Control
Early detection of aphid populations is critical to successful control. Drenches of systemic insecticides can provide successful long-term suppression of an aphid population. Foliar applications of insecticides are also effective but may require repeated applications to prevent infestation by frequent invasions of aphids or to protect newly expanded leaves or flowers. When applying insecticides, you must rotate modes of action between each spray as aphids are highly prone to developing resistance.
