A Great Spring for Aphids

This long spring is ideal for aphids. Colonies of the small sap-feeders (Figure 1) can be found on many landscape plants now. Impacts of aphids vary widely. Some species manage to remove sap without any obvious effect on plants. However, a plant’s reaction to injected saliva may result in severe distortion of new tissue (Figure 2). Other species may excrete large volumes of honeydew, producing sticky, shiny leaves that soon turn black with sooty mold.

Figure 1. An aphid colony developing around an adult female. (Photo: Lee Townsend, UK)

Figure 1. An aphid colony developing around an adult female. (Photo: Lee Townsend, UK)

Figure 2. Corrugated appearance of birch leaf from aphid feeding. (Photo: Lee Townsend, UK)

Figure 2. Corrugated appearance of birch leaf from aphid feeding. (Photo: Lee Townsend, UK)

Aphid infestations can develop from eggs laid on host plants the previous autumn or from winged aphids that fly to plants in spring. Winged aphids deposit several wingless young on tender tissue before moving on to find a new plant, scattering their offspring to increase chances of survival. Immature aphids, or nymphs, grow rapidly, maturing in 7 to 10 days.  Then they are ready to produce their own live young. Depending on the species and food quality, aphids may produce 20 to 40 offspring. The process is repeated several times, resulting in tremendous population explosions.

Management

  • Early detection is the key to reducing aphid infestations. Regular inspection of terminal foliage allows early detection of aphid infestations before symptoms develop and while control can be relatively easy and successful. Examine the bud area and undersides of the new leaves for clusters or colonies of small aphids. Small numbers of colonies on small plants can be crushed and infested leaves removed.
  • Watch for signs of natural enemies at work. Lady beetles (Figures 4 & 5) may be able to deal with moderate numbers of aphids.
Figure 4. Newly hatched lady beetle larvae (left) should soon find this aphid colony. (Photo: Lee Townsend, UK)

Figure 4. Newly hatched lady beetle larvae (left) should soon find this aphid colony. (Photo: Lee Townsend, UK)

Figure 4. Several empty lady beetle pupal cases are evidence of natural control at work. (N. Williamson)

Figure 4. Several empty lady beetle pupal cases are evidence of natural control at work. (N. Williamson)

  • Large, well-developed infestations may warrant an insecticide application on small or newly-established plants. Most products used for aphid control work as contact insecticides. Spray droplets must land on the aphids and be absorbed into their bodies. Thorough spray coverage directed at growing points and protected areas is vital. It is difficult to treat large trees because of the high spray pressure necessary to penetrate the foliage and to reach the tallest portions of the tree. Hose-end sprayers can be used on 15 foot to 20 foot trees but they need to produce a stream, rather than an even pattern, to reach these levels. Skips in coverage are common and there is a significant potential for applicator exposure through drift and runoff. Aphid control is rarely feasible or necessary on healthy plants.

 

By Lee Townsend, Extension Entomologist

Posted in Landscape Trees & Shrubs, Ornamentals