THE LEAF BLOTCH DISEASE OF HORSE-CHESTNUT 



V. B. STEWART 



The horse-chestnut (/Esculus hippocastanum) is common throughout 

 the State of New York. In public parks and private plantings the large, 

 magnificent trees, with their deep green foliage, are particularly attrac- 

 tive. Ordinarily they are not considered desirable for street trees, how- 

 ever, owing to the excessive water supply that they demand; but in 

 certain localities they have, been used extensively for street planting, 

 and in many cities the species is very prevalent. 



There is some objection to the horse-chestnut because of the frequent 

 yellowing and dying of the foliage during the summer. On trees that 

 have received but little attention, the foliage is in many cases so dense 

 that the inner leaves die and fall to the ground for lack of sunshine. It 

 is believed, however, that a large proportion of the yellowing and sub- 

 sequent death of the foliage may be attributed to leaf blotch, which is 

 the most important disease affecting the horse-chestnut (ALsculus hippo- 

 castanum) and the Ohio buckeye (AL. glabra). 



Leaf blotch is known in America and in Europe, apparently occurring, 

 to some extent at least, wherever the horse-chestnut or allied species 

 are found. It is not observed so commonly in northern Europe as in 

 southern Europe, and apparently is never so destructive in these regions 

 as in America. In the eastern part of the United States, where the horse- 

 chestnut has a wide distribution, the disease is frequently observed, and in 

 many cases a large proportion of the foliage on mature trees is affected. 



In nursery plantings leaf blotch is particularly destructive. In many 

 cases the seedlings are completely defoliated by midsummer, and as a 

 consequence their growth is greatly retarded. When the disease has 

 once become established in a block of young nursery trees it usually 

 causes considerable damage each year. The affected trees develop more 

 slowly than they would normally, and a longer period of time is therefore 

 required for them to attain a marketable size. Several plantings from 

 seed have been observed which had made practically no increase in size 

 for three seasons, due to the abundant occurrence of the leaf blotch disease 

 each year. 



Not only does premature defoliation check the growth of the young 

 trees, but apparently the trees affected are less able to withstand the 

 adverse conditions of the subsequent winter months. An injury and 

 dying back of the twigs and branches has been observed on trees that 

 were badly diseased the preceding summer. 



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