The Rose Manual (1933) 265-268
J H Nicolas
Rose Infections
Summer defoliation is not always due to disease, although diseases will precipitate it. Summer defoliation did not bother our fathers before the introduction of Austrian Briar blood. Austrian Briars will lose their foliage early because it matures early. It is the nature of the beast that nothing can change, and all their hybrids inherit that character in a greater or lesser degree. When the foliage is mature, the “cortex” or film of corky material that heals the pores where the leaf is attached to the branch begins to form, the leaf receives less and less nutrition from the plant and drops at the least provocation, spray or dust notwithstanding. Some varieties when plants are healthy will push on new leaves at the top as fast as the bottom ones drop and the plant retains its “activity,” but if the defoliation is premature and accelerated by disease faster than new foliage can be produced the plant goes dormant. Pernetianas are at best in regions of long vegetative season, like southern France, the birthplace of the race, divided in two distinct growing periods — an early spring and a long springlike autumn intervened by a hot summer, because there is enough growing weather when they awake from their summer rest enforced by natural defoliation to come again to a useful life, and the new growth has time to mature before winter, if winter there is. Pernetianas are out of place as autumn bloomers where the season is short between a late spring and an early winter.
Black Spot starts from the inside, but is induced and spread by outside atmospheric conditions. As proof of this Cochet offers the argument that black spot always attacks the older leaves as they mature. If it did start from outside it would attack the soft new foliage just as mildew does, but the moisture inside young foliage is in rapid motion to and from the roots and has no time to mold even when inoculated until that motion slows down in the process of maturity. Black spot is intimately related to the innate persistence of foliage, as above stated; long-lived foliages, such as pure Teas and species evergreen in their native habitats are immune. As Lambert said, “Have you ever seen black spot on bracteata, sempervirens, Cherokee?” When Pernetiana foliage has reached near maturity and the weather is humid, the moisture inside the leaves is not evaporated fast enough nor reabsorbed by the plant, and a fungus or mold forms just as clothes fresh from the aseptic laundry process will mold if put away moist.
Although black spot starts inside, the fungus fruits outside through punctures, and infection spreads rapidly to foliage already in process of maturing, there finding a fertile ground even if weather conditions were then normal for proper evaporation of excess moisture in the leaf tissues. This foliage has to be kept insulated by some medium. They do not like dust over there [in Europe] but prefer copper sprays. Another point brought to me to support that theory is that true Hybrid Teas do not take the spot until very late (if they do at all), when part of their foliage has naturally matured, which process is much later than Austrian Briar hybrids. Where summer weather is normally sultry, stick to the old line Hybrid Tea.
A Rose Odyssey (1937)
J. H. Nicolas
p. 12
Pernet was also well aware that his Pernetiana strain was not as universally adaptable as the Hybrid Tea. He did not expect it to conquer the world. He often remarked that he did not recognize his roses in Paris, less than three hundred miles away. He was an artist working primarily for his own enjoyment. The climate or atmosphere of Lyons is what we might call “anti-black spot.” Why, I do not know, but I suspect that soil alkalinity has something to do with it. He never knew what the accursed disease was until I showed him an infected leaf which it took me hours to find. This may be the reason why Pernet stuck so closely to his own original strain. I received today a catalogue from another firm at Lyons. In the rose-growing instructions the catalogue mentions mildew and rust, but not black spot. Happy country!
pp. 157-158
Lambert believes that black spot starts as “an old age infirmity”, because Austrian briar, which is on one side of the family of most susceptible varieties (Pernetianas), is a species of short-lived foliage. He says that the foliage gets prematurely old, ceases to function properly and becomes diseased. The spores then spread to younger foliage and defoliation occurs if the climatic conditions are propitious to the multiplication of spores. Lambert, corroborated by Father Schoener, claims that a strain of immune roses can be produced from species with long-lasting foliage, as experience has proved that evergreen and ever-growing types such as R. bracteata, R. longicuspis, R. glomerata, R. gigantea macrocarpa, etc., are absolutely immune to leaf diseases. He also believes that a careful selection of breeders in the mixed Hybrid Tea and Pernetiana classes would help in bringing about a more resistant strain.