Aphids in the southwest
Over the past few weeks, growers have seen numerous aphid infestations in greenhouse and nursery crops including zinnias, snapdragons, calibrachoa, Rhaphiolepis and Lagerstroemia. One grower commented that his crops are more heavily infested with aphids this spring compared to the past several years. His frustration at being told that aphids are usually easy to control is understandable because aphid control can be challenging.
Many types of aphids can be found feeding on ornamental crops. The most common are green peach aphid and melon aphid.
Because aphids are harder to detect than other insect pests, heavy populations can “sneak up” on growers. Aphids are often first detected when plant stunting or deformity from feeding is noticed or when sooty mold growing on aphid honeydew shows up on foliage.
Aphid symptoms and damage on crops
Aphids reproduce very rapidly because all aphids are females and each aphid gives birth to more females. No mating is necessary.
Aphid life cycle (7 days)
- Egg: Yellow, elliptical in shape, turning shiny black (overwintering stage)
- Nymphs: pale yellow to dull green
- 4 instars 2 days each (7-8 days)
- Adults: 20-23 days lifespan
- Reproductive rate:
- Melon aphids 4.3 nymphs/day
- Green peach 1.6 nymphs/day
- Over 30 generations/year
- Parthenogenetic – offspring develop from unfertilized eggs
Plant inspection and scouting are critical for finding aphid populations when they are low because starting control measures before an outbreak will produce much better results. Buds, stems and lower surfaces of leaves are areas where aphids will likely feed. Scouting for cast aphid casings on the upper surface of leaves can also help locate colonies. To locate winged aphids, yellow sticky cards can be used.
Aphids vs. fungus gnats – Photo by L. Pundt
Another tool in aphid management is the use of sentinel plants. When an infested plant is found, it is marked and monitored after treatment to determine how successful the treatment was.
Aphids found in the upper canopy or in plants with a sparse canopy are generally easier to control with contact sprays. Aphids feeding on older growth lower in the canopy are more difficult to control and those colonies produce new aphids that re-infest plants. In this instance, drenching with systemic products is more effective.
Systemic insecticides, like Mainspring® GNL, or translaminar insecticides, like Endeavor®, provide excellent control of aphids when the infestation is detected early. Coverage when spraying systemic, translaminar or even contact products, like pyrethroids, is critical because sufficient chemical has to reach where the aphids are feeding to achieve adequate control. Drenching with a systemic like Mainspring GNL can overcome the spray coverage issue in many crops.
About the author
Jan Couch is a Syngenta Turf & Landscape Territory Manager located in the Western US. You may also follow Jan on Twitter: