150 MISC. PUBLICATION 4 3 4, U. S. DEPARTMENT OF AGRICULTURE 



cleaning up the fallen leaves underneath older trees nearby and in 

 the nursery. The mixing of green ash with chokecherry within the 

 same row or in alternate rows may also reduce the amount of the 

 disease. Both species need to be sprayed and the mixing of the 

 green ash and chokecherry reduces the facility of spread of the disease, 

 since neither tree species is susceptible to the other's leaf disease. 

 Good fertility and adequate watering also appear to reduce the amount 

 of infection. 



Puccinia periodermlospora (Ellis, and Tr.) Arth., a true rust, occurs 

 occasionally on green ash. Regular spraying of green ash and Ameri- 

 can plum with bordeaux should likewise aid in controlling true rusts 

 which occur occasionally but generally are not serious in the Great 

 Plains region. 



The leaf disease of American elm, Gnomonia ulmea (Sacc.) Thuem., 

 which is quite common in the Gulf region and Eastern States, has not 

 been observed in Great Plains nurseries and need not be considered in 

 detail here. The appearance of any sudden dying of American elm 

 should be reported immediately, since this species is infected by several 

 virulent parasites in other sections of the country (8). 



Top Blights and Wilts 



Under the dry climate of the Great Plains area where water is usually 

 supplied by furrow irrigation, top infections of seedlings have not 

 been as common as further east. Conditions of high humidity and 

 excessive moisture may cause considerable loss. At North Platte, 

 Nebr., in the spring of 1937, black locust and Osageorange seedlings 

 were infected with a Corticium top blight following heavy rains. 

 Typically, top blight leads to a rapid wilting of the seedlings. The 

 serious seedling top infection of black locust caused by Phytophthora 

 parasitica Dastur as reported by Lambert and Crandall (19) has not 

 been observed in the Great Plains nurseries. 



Top blights are difficult to control once infection takes place. Con- 

 ditions which lead to poor aeration and high humidity should be 

 avoided when possible. Less dense sowing and adequate soil drain- 

 age will reduce losses from top infections. 



Mulberry blight demands special mention, as it sometimes causes 

 much damage in the Southwest and has been observed as far north 

 as Fremont, Nebr. Russian mulberry (Morus alba tatarica) seedlings 

 and older trees are known to be infected with this bacterial blight, 

 caused by Phytomonas mori (Boyer and Lamb.) Bergeye, et al. Young 

 seedlings first show the disease by the appearance of water-soaked 

 areas at the tips of the cotyledons which soon become withered and 

 dried. Frequently the infection extends down the petioles into the 

 stem, causing the seedlings to wilt over and die. The top of the 

 stem at first becomes withered while the base and the roots remain 

 healthy. 



Black lesions are also formed on the leaf petioles and stems of older 

 plants. These later develop into typical cankers which often split 

 open and exude the bacteria in yellowish droplets. Old cankers 

 sometimes become deep enough to expose the pith. 24 



24 Summary of unpublished report by Howard Lamb dated September 1935, Woodward, Okla. 



