Gall Insects

Forest Health Guide for Georgia Foresters
Written by Terry Price, Georgia Forestry Commission
Adapted for the web by the Bugwood Network

Galls are abnormal vegetative growths on trees that result from the feeding and egg laying activities of various insects and mites. Chemical secretions from the adults while laying eggs as well as the saliva from the feeding larvae cause the plant to react abnormally.

The more common gall producers on trees are aphids, beetles, jumping plant lice, midges, mites and wasps. Each species causes a swelling of plant tissue that is characteristic on specific plant parts such as the stem, twig, leaf or petiole. Most often the gall is more readily identified than the gall producer. It is convenient to identify galls and their producers simply by noting where the gall is located and also the shape of the gall. Table two lists some of the more common trees that are frequently attacked by gall producers along with a description and location of the gall.

Generally galls are not life threatening to trees. Oftentimes the most drastic effects are premature leaf fall and dieback of several smaller branches.

On small trees galls should be pruned and destroyed. Leaf and twig litter that is on the ground around the base of the tree should be raked and disposed of. A few of the common species are shown in (Figures 83-85).

Figure 83 - Cynipid oak galls
photo by Ronald F. Billings

Figure 84 - Wool sower galls on white oak
photo by Terry Price

Figure 85 - Leaf galls on black cherry
photo by Andrew J. Boone

Tree Location Gall Description Occurrence Name/Organism
Ash leaf reddish-brown bullet shaped summer ash bullet gall/midge
  midrib swollen ¼"-½" summer ash bullet gall/midge
Beech leaf white/buff velvety pile summer Erineum gall/mite
Birch seed swollen infertile spring birch seed midge
Boxelder bud ½"-1" swollen spring boxelder bud gall/midge
  leaf nearly spherical, 1/10" diameter spring-summer boxelder leaf gall/midge
Cherry, Black twig irregular black swellings year-round back knot/fungus
  bud/shoot irregular red or yellow spring wild cherry bud gall/midge
Chestnut bud swollen bud or petiole spring chestnut bud gall/wasp
Dogwood twigs club-shaped swellings summer dogwood club gall/midge
  stem irregular ½"-1" summer dogwood stem gall/midge
Hackberry petiole kidney-shaped summer hackberry petiole gall/ plant lice
  stem irregular ½"-1" summer dogwood stem gall/midge
Hackberry petiole kidney-shaped summer hackberry petiole gall/ plant lice
  leaf Large nipple-like summer hackberry nipple gall/ plant lice
Hickory leaf cylindrical, green slanting summer hickory tube gall/midge
  twig/leaf stem new galls-green, old galls black spring-summer hickory gall/phylloxeran
Locust, Black leaflets folded early summer locust midge
&npsp; twig/stem fusiform swellings summer locust twig gall/midge
Locust, Honey leaflets folded or marginal leaf rolls early summer honey locust gall/midge
Maple leaf sac-like summer maple bladder gall/mite
Oak leaf various shapes summer-fall oak apple galls/wasp
  bud urn-shaped spring-summer leafy oak gall/wasp
Pine new shoots spindle shaped spring-summer pine gall sawfly
  twigs/stems globular resin masses spring-summer southern pitch midge
Poplar petiole globose ridged summer ribbed petiole gall/moth
  leaf, stem, petiole oval with transverse openings summer poplar leaf stem gall/aphid
Willow branch/stem globose galls summer willow borer/beetle
  bud/leaf various shapes spring-summer various names midge/sawfly

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