Sunday, June 24, 2012
Do you know what a gall is? You should!
Eastern spruce gall
A gall is defined as a
A common gall her in Illinois is the Eastern Spruce gall, which is really just a type of aphid. They love to host on Norway and white spruces, but will attack any spruce.
The pineapple-shaped galls greatly stunt the growth of new spruce shoots. Trees demonstrate a wide range of susceptibility, some have many galls which kill the branch and others having few galls which allow for continued branch growth.
The aphid-like insect called an adelgid (Adelges abietis) makes the gall. These insects were active in the spring and caused the gall to begin forming at that time. These galls are often mistaken for small cones. With Eastern spruce gall, the gall forms at the base of the new growth. (There is another gall known as Cooley spruce gall which has a similar shape, but forms on the tip of the new growth). The galls mature in midsummer and slits appear that allow the mature adelgids to leave the gall.
Management: While the galls will kill the new growth on which they form, infestations in our area are seldom heavy enough to require any type of management. Galls can be removed by hand before the slits open. Insecticides are seldom warranted but can be applied in early spring right before bud break or in late September and October.
The life cycle is completed on a single suitable host plant. Well timed sprays are generally the most effective controls, if control is really needed.
Strategy 1: Use of Resistant Varieties - Black, red and Englemann spruces are generally less susceptible to this pest. However, certain cultivars of Norway and white spruces have demonstrated some resistance. Try to select uninfested nursery stock which has not been sprayed regularly for control of this pest. Trees lacking galls are more likely to be resistant.
Strategy 2: Dormant Oil Sprays - Dormant oil, applied in October and November or in April, is very effective against this pest. Be sure to use a good quality oil and spray before buds have doubled their winter size. Glaucous (bluish blush) trees will turn dark green when sprayed with oil.
Strategy 3: Fall Insecticide Sprays - Insecticides can be applied in September and October to kill the alate non-migrans and overwintering fundatrices. See Bulletin 504 for the currently listed insecticides.
Strategy 4: Spring Insecticide Sprays - Insecticides can be applied in mid-April before the fundatrices mature and lay eggs. This is usually before the bud sheaths become loose. See Bulletin 504 for the currently listed insecticides.
For additional information on the Eastern Spruce Gall: Good websites: http://www.hort.uconn.edu/ipm/homegrnd/htms/59spgall.htm
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Thanks for reading,