ILLINOIS NATURAL HISTORY SURVEY 



CIRCULAR 53 



Fig. 1 . The earliest 

 visible symptoms of 

 Dutch elm disease are the 

 wilting, curling, and yel- 

 lowing of leaves on one or 

 a few branches. On this 

 tree the wilted and curled 

 leaves are evident on the 

 branch at the left. 



wilt and die rapidly probably became infected during the previous 

 growing season, at which time they would have shown no wilt symp- 

 toms or only limited and relatively inconspicuous symptoms. 



Brown streaking develops in the sapwood of diseased branches. 

 It appears mostly in the springwood of the current-season growth. 

 In a cross-section of a branch, browning may appear as a series of 

 dots in a single wood ring (Fig. 3) or the dots may be so abundant 

 that the entire wood ring appears brown. In branches on which leaves 

 wilt before summerwood is produced, the discoloration is usually 

 conspicuous as fine streaks on the surface of the wood when the bark 

 is carefully peeled from the diseased branch (Fig. 4). The outer sur- 

 face of sapwood on trunks may also be brown (Fig. 5). 



The presence of brown discoloration in young sapwood is used 

 in the field as a diagnostic symptom of Dutch elm disease. Although 

 several wilt diseases of elm cause similar browning of young sap- 

 wood, trees showing this discoloration in areas where Dutch elm 

 disease occurs are most likely affected with Dutch elm disease. How- 

 ever, if the presence of the fungus in the tree must be determined, it 

 is necessary to make laboratory tests of specimens from the diseased 

 tree. With these tests the organism involved is isolated and the spe- 

 cific disease present is determined. However, in some instances the 



