NURSERY PRACTICE FOR PRAIRIE-PLAINS PLANTING 151 



The manner in which the disease is spread is not definitely known. 

 In greenhouse tests at Lincoln, Nebr.. no bacterial blight was ob- 

 served on the seedlings grown from southern mulberry seed sown in 

 different soils, including those from Oklahoma and Texas. The indi- 

 cations are that the bacterium is probably disseminated by wind and 

 rain more commonly than by seed, but insects may also act as carriers. 

 A combination of all four ways is possible. It has been observed. 

 however, in the field that the heaviest infection of mulberry seedlings 

 commonly occurs adjacent to older mulberry plantings, which tends 

 to verify the statement that seed-borne dissemination of the diseax* i- 

 of minor importance. Seed should not be collected, however, from 

 obviously diseased trees. It is advisable to locate the mulberry 

 seedlings in a part of the nursery as far removed as practicable from 

 older mulberry plantings. 



The dusting of mulberry seed with bordeaux and zinc oxide dusts 

 in field trials has failed to give satisfactory results. It appears advis- 

 able to spray the seedlings regularly with bordeaux of the 4-6-50 

 strength in nurseries where the disease has appeared. Spraying 

 should be started just as soon as the cotyledons appear above the soil 

 and should continue at intervals for several weeks. Spraying is 

 especially desirable following rains. Reducing the density of the 

 seedling's per unit area should aid in preventing a rapid spread of the 

 disease from plant to plant. 



Miscellaneous Diseases 



Dodder (Cuscuta sp.) is not a fungus but a flowering plant related to 

 the morning-glory family, nevertheless a true parasite of other plants. 

 Dodder has caused some damage to tree seedlings and has been found 

 growing on black locust, green ash, cottonwood and desertwillow in 

 Midwest nurseries. It appears as a fine, yellow, vinelike growth, 

 sometimes occurring so dense as to completely cover the tops of the 

 seedlings. It spreads by seed or directly from seedling to seedling. 



The embryonic Cuscuta plantlet, coiled up in the seed, pushes up 

 through the ground in early spring, but makes little use of its cotyledons 

 as a means of nourishment. No underground root system develops 

 from the young rootlet which soon dies. The dodder seedling early 

 develops into a long, thin filament, the free end of which is for con- 

 tacting plants from which nourishment is obtained (37, pp. 189-190). 

 A direct connection forms between the conducting vessels of the host 

 and those of the parasite as the vine coils around the parasitized plant. 

 The organs of connection are known as "haustoria." The sapping of 

 water and nourishment from the host plant causes a stunted growth 

 of infected seedlings, and heavy infection may kill the host plant. 



Dodder can be removed from the seedlings with a rake similar to a 

 currycomb which may be made by driving nails through a board to 

 which a handle is fastened. Upon removal from the plants, the dodder 

 should be destroyed by burning. Sometimes it spreads from Dative 

 vegetation at the margins of a nursery. Cleaning away the native 

 vegetation, creating a barren border around the nursery, would be good 

 insurance against widespread infection. Dodder can also be intro- 

 duced with rotation crop si^etl and care should be taken to use cleaned 

 seed. 



