NURSERY PRACTICE FOR PRAIRIE-PLAINS PLANTING J 49 



given by the manufacturers to obtain a solution equal in strength to 

 a 3-4-50 home-made mixture should be used. McNew and Bliss (25) 

 in Iowa recommend a 4-6-50 mixture for commercial cherry varieties. 

 It is essential in any case to spray as soon as the leaves appear and 

 repeat the applications throughout the growing season, especially 

 following rains. Spreaders are sometimes recommended for better 

 coverage and adhesiveness. Whale-oil soap, casein, linseed oil, and 

 a good grade of soap chips are sometimes used as spreaders. The 

 first two are used at the rate of about 2 pints in 50 gallons of spray 

 solution, while the last two require about 5 pints or pounds per 50 

 gallons. A good emulsion is required for best results. Skim milk 

 used at the rate of 1 gallon in 50 gallons of spray solution is a cheap 

 and effective spreader. 23 



In other sections of the country it has been reported that the 

 bordeaux concentrations advised above have caused severe burning 

 of the foliage. It is likewise essential to maintain the vigor of the 

 seedlings since there are some indications that the addition of ni- 

 trogenous fertilizers and adequate water appear to render the seedlings 

 less susceptible to leaf diseases. 



Spray applications made after the shot hole appears will not control 

 the disease on infected leaves. Late spray applications appear to 

 retard the infection of new leaves, but early and repeated applications 

 are necessary for really satisfactory results. 



It is known that the fungus overwinters on dead leaves and it is 

 advisable, therefore, to dispose of the fallen leaves in the nursery by 

 burning or by plowing the leaves under in the fall. Susceptible 

 species should not be sown on the same ground the following year. It 

 is also desirable to strip all leaves from the seedlings at time of bundling 

 to prevent carrying the disease to the field where the seedlings are 

 planted. 



The rust Tranzschelia punctata has been observed on P. americana 

 but only to a limited extent. 



A leaf disease of green ash (Fraxinus pennsylvanica lanceolata) is 

 quite common in the Midwest, especially in northern nurseries. 

 This disease is referred to by nurserymen as leaf rust. It is not a 

 true rust, however, since it is caused by Marsonia sp. It is most 

 evident in mid to late summer when the upper surface of the leaves 

 assume a rustlike appearance. By close examination small black 

 spots will be found on the under surface of infected leaves. These 

 are the fungus fruit bodies. 



The disease causes premature defoliation resulting in decreased 

 growth. This is very undesirable for green ash since it is not a rapid 

 growing species in northern nurseries even under normal conditions. 



So far, spraying with lime sulfur and bordeaux of various concen- 

 trations have given somewhat disappointing results in the control of 

 this disease; however, spraying operations are rarely started early 

 enough or repeated consistently enough for satisfactory results. 

 Numerous applications of bordeaux spray, as suggested for choke- 

 cherry above, probably will give satisfactory control. 



It is further suggested that green ash seedlings should be grown 

 in a portion of the nursery as far removed from older green ash trees 

 as practicable. The amount of local infection can be reduced by 



23 Davis, W. C, Young, G. Y., Latham, D. H., and Hartley, Carl, debases of conifers in korest 

 nurseries. U. S. Bur. of Plant Indus. 1938. [Mimeographed.] 



