DUTCH ELM DISEASE 5 



entered four ports of the United States from Europe during the period 1925 

 to 1934. These logs were delivered by rail to points in the Central and Mid- 

 western States for manufacture into veneer products. Seven small centers of 

 disease infestation have been reported as traceable to imported logs, in addition 

 to the severe infestation in the New Jersey-New York area. Furthur im- 

 portation of elm material is outlawed by present federal quarantine regulations. 



Symptoms 



The disease may occur in an acute form evidenced by conspicuous, imme- 

 diate, and severe wilting (Figure 1). Other cases in which wilting lacks the 

 suddenness characteristic of an acute attack, have been described as chronic. 

 In acute attacks, at first the young leaves and, within a short time, the leaves 

 of the entire tree wilt and wither. If the wilting is particularly sudden, the 

 leaves dry and curl before they turn completely brown or even while they are green. 

 A short time after the wilting starts, the dried and curled leaves begin to fall 

 and within a few weeks most of the leaves will have fallen. If the twigs 

 wilt while they are still green, the retention of the end leaves and crooking of 

 the twig tips are typical early symptoms (Figure 1, insert). The bark on the 

 affected trees from which the leaves have fallen shows no immediate character- 

 istic disease symptoms which would distinguish it from the bark of healthy 

 trees. Within a short time after the leaves have fallen from diseased trees, 

 however, scolytid beetles may infest the bark. The larvae of these beetles 

 are frequently found in considerable abundance under the bark of trees recently 

 defoliated. It is important to note that these beetles, when present under the 

 bark, should not be considered as primary invaders inasmuch as the trees so 

 infested have previously been weakened and usually seriously defoliated. 

 An examination of the wood of such an infested tree should show additional 

 disease characteristics if the tree has been affected by the Dutch elm disease. 

 Frequent reports of observations of this kind have been made during the periods 

 from June until late August. 



The chronic type of the disease differs from the acute type mainly in the 

 length of time required for the pronounced symptoms to appear on the affected 

 trees. In some cases the entire summer may be required for the complete 

 defoliation of a tree by this gradual process. During the relatively slow 

 progress of the disease in such cases, individual branches bearing yellowed or 

 wilted leaves, commonly called "flags," may frequently be observed in the tops 

 or in other parts of the trees. Early dropping of the leaves which first showed 

 discoloration is a rather common occurrence. It must be borne in mind, 

 however, that not all early yellowing and wilting of elm leaves is caused by the 

 Dutch elm disease since other diseases, certain insects, and some other types 

 of injuries may cause defoliation. 



In some cases "flags" may not appear in any part of an affected tree, but 

 rather a gradual discoloration of the leaves over the entire tree may occur 

 during the summer. The general appearance in such cases is like that of 

 premature autumn coloration. Early defoliation of the entire tree or parts of 

 it frequently results. 



Still another chronic type of the disease has been observed in which the 

 affected trees leaf out rather late or fail to develop leaves on some branches. 

 The foliage may be sparse, chlorotic in appearance, and drop prematurely 

 during the summer. The stag-head which eventually develops from the 



