I have nothing to add to this. I just thought it might be worth some attention.
https://archive.org/stream/americanrose ... 1/mode/2up
American Rose Quarterly 1(1): 15 (March 1930)
Understocks and Black-Spot
An interesting observation has been made by one of the keenest rosarians in America, who believes that roses on the cutting Brier understock, i.e. root cuttings of Rosa canina, are much more resistant to black-spot and possibly other rose diseases than those on some of the more commonly grown stocks. The Editor would be glad to have confirmatory or contradictory experiences in this respect. Have any other members observed a similar resistance in roses grown on R. canina?
https://archive.org/stream/americanrose ... rch/canina
American Rose Quarterly 1(2): 38-39 (June 1930)
Understocks and Black-spot.— The Editor has had several comebacks concerning the suggestion made on page 15 of the March Quarterly that roses rooted on cuttings of Rosa canina seem to be more resistant to black-spot than those on other stocks, not the least interesting of which is the following comment from Dr. T. Walker Weaver, of Wichita, Kans.: "A small editorial comment on an observation made by some rosarian that roses grown on R. canina understock were less liable to black-spot, and perhaps some other diseases of which roses are heir, caught my eye. This observation has been made by myself and a friend who grows good roses (T. Livingston). It is our thought that the reason this is true is perhaps due to our climatic and soil conditions. Summers here are hot and dry. The soil is a sandy loam with water flowing six to eight feet below the topsoil in most places. Now roots of R. canina are not so many, but much longer in this country, going deep into soil where it is cool and damp. Roots of R. multiflora, on the contrary, are more fibrous and do not go nearly so deep into the soil for nourishment, so that the plant flourishes in spring and fall. July and August, however, are hard on plants on this understock here.
"We have all made the observation that strong, vigorous plants are not nearly so susceptible to black-spot as weaker ones. I believe that when understocks are more carefully worked out for different parts of the country, roses will be much more easily grown."
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