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



Late root rot so far has occurred in the Great Plains region only 

 in northern nurseries on comparatively heavy soils. Corticium 

 solani has been found in association with a late root rot of Caragana 

 arborescens. The tips of the tap roots and many small lateral rootlets 

 were rotted back and destroyed, resulting in a heavy mortality for 

 seedlings several weeks old. At another nursery the roots of sumac 

 (Rhus trilobata) showed similar symptoms, but a Fusarium was com- 

 monly isolated. At still another nursery, Siberian elm making un- 

 satisfactory growth showed stem lesions at the ground line, but only 

 apparent saprophytes could be isolated from the decaying parts. 



No definite control measures are yet known, but it appears that 

 the overabundance of organic matter and poor aeration are probably 

 factors contributing to an increase of late root-rot infections. 



Leaf Diseases 



Leaf diseases in general reduce the rate of growth and subsequently 

 interfere with food reserves. In orchard trees, for example, it is 

 known that where leaf spots have been severe the trees are frequently 

 damaged by frost and drought. The impoverished fruit trees are 

 unable to resist adverse conditions in the field as well as normal 

 trees. In the nursery where the food-synthesizing activity of the 

 leaves is retarded because of leaf diseases, the growth of the seedlings 

 is frequently reduced so much that they do not reach usable size by 

 the end of one growing season. When the seedlings do reach usable 

 size the decreased food storage may limit the ability of the tree to 

 produce roots after field planting. Leaf diseases are, therefore, of 

 considerable economic importance and the nurseryman should not be 

 misled by the fact that the plants do not appear to be seriously injured. 

 Fortunately, not many broadleaf species have serious leaf diseases. 

 Chokecherry, other species of Prunus, and species of ash are the most 

 susceptible to leaf diseases in the Great Plains region. 



Chokecherries (Prunus virginiana and P. virginiana melanocarpa) 

 are commonly infected with a leaf spot disease caused by Coccomyces 

 lutescens Higgins. This disease is referred to as shot hole. Infec- 

 tions first appear upon the foliage as small yellow or reddish circular 

 spots which later turn brown. Eventually the dead brown spots may 

 become separated from the surrounding leaf tissue and fall out, pro- 

 ducing the typical shot hole. In severe stages, the disease causes a 

 yellowing of the tissues between the lesions, giving the infected foliage 

 a striking chlorotic appearance and causing the leaves to fall pre- 

 maturely. The lower leaves usually fall first. Black cherry (P. 

 serotina) is perhaps even more susceptible to shot hole than choke- 

 cherry, but American plum (P. americana) appears quite resistant. 



The serious nature of the shot hole disease on species of Prunus 

 necessitates from five to seven spray applications for control. Home- 

 made bordeaux spray used as a 3-4-50 mixture 21 appears to give 

 satisfactory control when applied early in the season and repeated at 

 frequent intervals of a week or 10 days 22 in Midwest nurseries. For 

 the concentrated bordeaux powders now on the market, directions 



21 3 pounds copper sulfate and 4 pounds rock lime to 50 gallons of water. For the rock lime, 5 pounds of 

 the more generally available hydrated lime may be substituted. 



2 2 Young, George Y. spraying as a control of leaf diseases on nursery stock of fraxinus 

 and prunus species in the upper Mississippi valley. Soil Conserv. Serv. 1939. [Unpublished 

 memorandum.] 



