Psyllids are jumping plant lice that suck plant juices. There are over 160 psyllid species in California, 140 of which are native to the area.
Most native psyllid species do not pose a serious threat to your garden. Local predators tend to keep those populations in check most of the time. Invasive psyllid species are something else altogether.
Psyllids look like tiny cicadas or winged aphids, with tubular mouthparts. They have very strong legs and short antennae. Psyllids can be 1/12 to 1/5” long. Adults hold their wings in a roofline position. Nymphs are flattened and look a lot like soft scale insects. Psyllid nymphs commonly produce waxy filaments or covers, called lerps. Lerps are made from wax and honeydew.
Regardless of the species, psyllids start out as tiny eggs that hatch and go through five developmental stages, or instars, before reaching adulthood. Adult psyllids can fly, but most prefer to jump. If you see what you think is a psyllid run or fly away, it is probably a psocid [SO-sid]. Psocids are beneficial insects that feed on fungi. They differ from psyllids in that they have a narrow “neck” and chewing mouthparts.
Psyllid host plants
As a species, psyllids have strong preferences for particular host plants. While some psyllids will prefer your sweet peppers and chili peppers, other varieties will go after your peaches and nectarines, while others will only feed on olive or pear trees, and yet other psyllid species will only feed on potato and tomato plants.
The invasive Asian citrus psyllid carries huanglongbing, a deadly citrus disease. Orange, lemon, lime, kumquat, and grapefruit trees infected with huanglongbing must be destroyed by a professional. Sad, and expensive. These pests, when present, are most active April through June in the San Francisco Bay Area.
Psyllid species most likely to threaten your garden include:
There are dozens of psyllid species that infest ornamental trees and shrubs, as well. These include the recent invasions of Ficus leaf-rolling psyllids and spotted gum psyllids. On the other hand, some psyllid species are being used to our advantage. The Australian melaleuca psyllid, for example, has been purposefully introduced to Florida to help control paperbark trees, an invasive weed tree.
Damage caused by psyllids
One of the biggest problems associated with psyllids is their poop. After they have robbed your plants of valuable nutrients, weakening the plant, they add insult to injury by excreting a large portion of the sap they stole and depositing on leaves. Known as honeydew, the excrement of sap-suckers is filled with sugar and other nutrients. Honeydew ends up being food for fungal sooty mold and disease-carrying ants.
Psyllid feeding can also spread viral diseases, such as calico, bacterial diseases, such as zebra chip, galls, leaf and bud discoloration and deformation, and premature leaf drop. Leaf distortions often look similar to peach leaf curl. Pear psyllids inject fruit with toxins that blacken leaves and fruit skins. Psyllid feeding also creates points of entry for other pests and diseases.
How to control psyllids in the garden
Once psyllids appear in your garden, insecticidal soaps and yellow sticky sheets can be used to help control them. Parasitic wasps and pirate bugs can put a serious dent in psyllid populations, so avoid using broad spectrum insecticides. Severely infested plants should be removed and destroyed or thrown in the trash. Usually, simply monitoring plants regularly can make controlling these and other pests much easier.
To prevent invasive psyllids from finding your garden, only buy pest-free plants from reputable nurseries, place new plants in quarantine, and do not bring plant products that may be infested into your state, community, or yard.
Because of the risks posed by invasive psyllids, any unrecognized psyllids should be taken to your agricultural commissioner or local County Extension Office for identification.
You can grow a surprising amount of food in your own yard. Ask me how!