Aug. 4, 1923 
Systemic Infections of Rubus with Orange-Rusts 
239 
DISTRIBUTION OR THE ORANGE-RUSTS 
The long-cycled Gymnoconia is the only orange-rust known in Europe 
and Asia. When it was discovered that there were two of these rusts in 
North America it was said that the short-cycled form was southern in its 
distribution and the long-cycled strictly northern, the former being the 
rust so destructive to the blackberries and dewberries grown commer¬ 
cially. It is now known that it is no longer necessary to make pilgrimages 
to Bartlett, N. H., for the Gymnoconia, because this rust thrives wherever 
the black raspberry, Rubus occidentalism or its susceptible horticultural 
varieties may grow. The writer has reported (5) that the rust is common 
on blackberries near Washington, D. C., and at Old Fort, N. C. He has 
since found it in abundance on blackberries at Salem, N. C., the type 
locality of “Kunkelia nitens ” and at Cornelia, Ga. Germination tests 
reported in a letter to the author by Dr. Dosdall, mycologist at the 
Minnesota Agricultural Experimental Station, show that the Gymno¬ 
conia is probably very common in that State. No doubt it will be found 
wherever susceptible blackberries grow. The short-cycled rust, having 
been recently derived from the other form, is less widely known. Its 
spread undoubtedly has been accelerated by commercial shipments of 
diseased nursery stock from one part of this country to another. The 
temperature ranges through which the Gymnoconia thrives are not dif¬ 
ferent from those suitable for the short-cycled rust, once each is 
established in its host. One reason why the Gymnoconia follows 
the black raspberry north and south and why this host is not attacked, 
at least to any extent, by the short-cycled rust, is that the teleutospores 
mature at the same time that susceptible tip plants are being developed. 
CONTROL OR THE ORANGE-RUSTS 
Methods by which the orange-rusts can be eradicated have been sug¬ 
gested in connection with the discussions of the infection experiments. 
It was pointed out that a blackberry can be freed from the orange-rust 
very easily if the task is undertaken soon after the primary infection be¬ 
comes manifest. The mere snapping off of the infected cane at the point 
of attachment to the root will suffice in many cases. When a number of 
shoots in the form of a witch’s broom are found, it usually indicates that 
the fungus has invaded the root or its crown; it will then be necessary to 
destroy this part of the root also. If the primary infection, however, is 
allowed to spread to the crown and root system the second year, so that 
new shoots are systemically and secondarily infected, the whole plant 
must be dug up, care being taken to include the roots for some distance. 
It has been shown that it is of the greatest importance to begin a 
planting with rust-free nursery stock. If the black raspberry to be used 
has been propagated by rooting the tips of canes one may be reasonably 
sure of getting some infected plants—that is, if the telial stage of the 
Gymnoconia is present in the nursery. Whether the tips of canes can 
be made to root early enough to avoid infection by the first sporidia 
from teleutospores or late enough so that no buds or shoots that can be 
infected are formed before the frosts, are problems which will require 
further investigation. If nurserymen will destroy all infected canes 
before aecidiospores are shed, there will be no teleutospores in their 
propagating fields, and it follows that their tip-plants will not be in¬ 
fected when sent to the grower. 
