Richard M. Houseman and Bruce A. Barrett
Division of Plant Sciences
Hackberry psyllids are tiny, jumping plant lice (family Psyllidae) that infest hackberry trees. Several species of psyllids infest hackberry. The most common is Pachypsylla celtidismamma. They resemble miniature cicadas (about 1/6 inch long) and are a dark, mottled-gray color (Figure 1).
Hackberry psyllids are often called hackberry nipplegall makers because nipple-shaped galls about 3/16 inch wide and 1/4 inch high develop on the underside of infested leaves (Figure 2). The gall, an abnormal plant growth on leaves or stems, results from complex chemical interactions between developing insects and plant tissues. As a gall develops, it becomes a "house" where the immature insect resides. Most infested leaves contain several galls, and host trees apparently do not suffer seriously, although galls are normally considered unsightly.
Adult psyllids emerge from galls in September and can be annoying to people living near infested trees. Psyllids will swarm to houses, particularly light-colored ones, in search of protected locations to pass the winter. They are attracted to lights at night and are small enough to pass through ordinary window screening. In some instances, large numbers gain entry into a home and become a nuisance. Psyllids do not bite people, pets or houseplants — they are pests only because of their unwanted presence.
After the onset of winter, psyllids generally are not active; however, they may mistakenly come out of dormancy on warm winter days and may create a minor nuisance. The biggest nuisance normally occurs during spring, when they break dormancy and fly about indoors, looking for places to exit the structure.
Nipple galls on underside of hackberry leaves.
The most effective control measure may be the removal of hackberry trees around the perimeter of the home. However, this may be undesirable or impractical, especially if there are hackberry trees in nearby yards.
If removal of trees is undesirable, an insecticide may be applied to the leaves during a time when psyllids are vulnerable. They are most vulnerable in the spring when newly hatched nymphs are beginning to feed but before protective galls have formed. A good rule of thumb is to apply the spray when the leaves have reached about one-fourth of full size. Several over-the-counter insecticides are available. Check the label to make sure it includes this insect.
It is important to note that treating hackberry plants will not solve a problem during the fall when hackberry psyllid activity is highest. In the fall, fine mesh (18) screening on windows and reduced lighting through windows and doors at night can help minimize invasions.
Aerosol sprays can be applied to screening and window and door frames to help minimize invasions; however, you must read the insecticide label closely to ensure it allows for this type of treatment. Indoors, use a vacuum cleaner to remove psyllids. Seal the bag completely and discard it immediately after vacuuming to minimize escape and reinvasion. If you have a large fall invasion, inspect and remove psyllids that may be present in the attic.
An aerosol insecticide labeled for "flying insects" can also be used to kill flying psyllids indoors. Aerosols that contain synergized pyrethrins or pyrethroids are effective. These active ingredients usually have names that end in -thrin. Treating wall voids or attics with an aerosol spray or dust is less effective.
Apply chemicals only where needed or justified. Before using any chemical, please read the label carefully for directions on application procedures, appropriate rate, first aid, storage and disposal. Make sure that the chemical is properly registered for use on the intended pest and follow all other label directions. Keep insecticides in original containers, complete with labels, and keep them out of the reach of children and pets. Do not allow children or pets near treated areas before these areas dry. Carefully and properly dispose of unused portions of diluted sprays and empty insecticide containers.