Extension News

Ask the ISU Extension Garden Experts: About Trees

sycamore with anthracnose

Note to media editors: Got gardening questions? Call the Hortline at 515-294-3108, Monday-Friday from 10 a.m. to noon and 1 to 4:30 p.m., or send an e-mail to hortline@iastate.edu. For more gardening information, visit us at Yard and Garden Online, www.yardandgarden.extension.iastate.edu.


My sycamore tree is dropping its leaves.  Is the tree dying? 
The sycamore is not dying. The leaf drop is likely due to anthracnose. Anthracnose is a common fungal disease of sycamore, ash, maple, oak and other trees. Anthracnose is most severe in years with cool, wet spring weather. While anthacnose may cause extensive defoliation, it does not cause serious harm to healthy, well-established trees.

Symptoms of anthracnose on sycamores include brown blotches on the leaves, death of young buds and shoots, and leaf drop. In cool, wet springs, affected sycamores may lose most of their initial foliage.

Fortunately, the sycamore trees will continue to produce additional leaves and shoots through early summer. Foliage that develops in late spring and early summer shouldn’t become infected as warmer, drier weather suppresses anthracnose. Most sycamores should have a good canopy of leaves by late June or early July.

Since anthracnose does not cause serious harm to sycamores, fungicide treatments are rarely warranted.

How often should I water a newly planted tree? 
The key to watering newly planted balled and burlapped and container-grown trees is to keep the plant’s root-ball moist for several weeks after planting. Water newly planted trees every day for six or seven days and then gradually reduce the frequency of watering. When watering, slowly apply water to the root-ball and the surrounding soil. A thorough watering every seven to 10 days (in dry weather) should be sufficient four to six weeks after planting. Continue this watering schedule through summer and into fall. Small trees usually require watering for one or two growing seasons. It may be necessary to periodically water large trees for two or three years.

There are erect, hair-like growths on the upper leaf surface of my maple tree. Should I be concerned? 
The hair-like growths are likely galls. Galls are abnormal growths of plant tissue induced to form by mites, insects or other small organisms. The hair-like gall on the maple leaves is probably the maple spindle gall.

Maple spindle galls are yellowish green and about 1/5 inch long. They are as thick as the lead in a pencil. The galls are somewhat thicker in the middle than at the ends, hence the common name of spindle gall.

Maple spindle galls are caused by extremely small mites that are only 1/125 inch long. The adult mites spend the winter under the bark and other protective places on the trees. In the early spring, the adults move to the developing, unfolding leaves and begin feeding. The leaf responds to the small irritation by rapidly producing extra cells that form the abnormal growth at the feeding site. The gall encloses the mite which continues to feed and lay numerous eggs within the gall. Reproduction is prolific and as the new mites mature, they leave the gall and move to other newly emerging leaves to repeat the process. Only new leaves are capable of producing galls. Mite activity continues until mid-summer when it starts to decline. Adult mites leave the foliage in the fall and move to the overwintering sites.

While galls, such as the maple spindle gall, are unsightly, they do not cause serious harm to healthy, well-established trees. Galls cannot be “cured” once they have formed. Preventative insecticide treatments are seldom warranted.

Contacts :

Richard Jauron , Horticulture, (515) 294-1871, rjauron@iastate.edu

Willy Klein, Extension Communications and External Relations, 515-294-0662, wklein@iastate.edu

Download photo: Sycamore defoliation