Decbmbeb 25, 1919. 



The Florists^ Review 



17 



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SUBDUING SNAPDRAGON RUST 



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|HESE sug^gestions on the 

 combating of snapdragon 

 rust will serve as a supple- 

 ment or sequel to a report 

 written by Charles C. Eees, 

 of the agricultural experi- 

 ment station at Urbana, 111., 

 and printed on page 35 of The Review 

 of December 11, with illustrations 

 showing the ravages of the disease. It 

 is unnecessary here to describe the dis- 

 ease or to give an account of its origin 

 and distribution, as that part of the 

 subject was fully treated by Mr. Reea. 

 The present article consists chiefly of 

 excerpts from a bulletin prepared by 

 George L. Peltier, who is also connected 

 with the Urbana institution. 



Some of Mr. Peltier's statements, 

 based on the results of experiments, 

 will be noted with special interest. He 

 reaches the conclusion that 

 the ordinary fungicides are 

 of no avail in the treatment 

 of snapdragon rust, and 

 that two of the best 

 methods of resisting the 

 disease are to avoid syring- 

 ing and to use stock grown 

 from seed in preference to 

 that grown from cuttings. 

 His testimony in favor of 

 seedlings is strong and ex- 

 plicit, with the one reserva- 

 tion that the plants may 

 not come true from seed, 

 since "few strains are 

 fixed." 



percentage of leaf infection was lower 

 than in any of the sprayed sections ex- 

 cept one. In other words, this treat- 

 ment was just as effective in the con- 

 trol of rust as were Bordeaux and am- 

 moniacal copper carbonate when ap- 

 plied every week. In house No. 2 prac- 

 tically the same results were obtained, 

 except that the infection was not so 

 great or so uniform, because natural 

 infection only was used. 



J 



Important Inferences. 



/ 



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From the results of these experi- 

 ments, then, it may be concluded that 

 the fungicides used will neither pre- 

 vent, check nor control snapdragon rust 

 in the greenhouse; it can be further 

 concluded that by watering the soil 

 only, in the bench, and avoiding all 

 syringing, the disease can be held in 



Failure of Fungicides. 



POINTS IN PREVENTION. 



The use of Bordeaux or ammoniacal copper carbonate 

 can neither prevent, check nor control snapdragon rust 

 in the field or in the greenhouse. 



Mr. Peltier relates how a 

 north bench in each of two 

 houses was planted with 

 stock of several leading 

 varieties of snapdragon, 

 for purposes of experimen- 

 tation. The principal dif- 

 ference in the treatment in 

 the two houses was that in 

 house No. 1 the plants 

 "were inoculated, or arti- 

 ficially infected with rust 

 spores for two or three 

 days after each spraying," 

 while in house No. 2 "nat- 

 ural infection was depended on, that 

 house having been used the previous 

 season in the rust work." Each of the 

 two benches was divided into ten sec- 

 tions, separated by double cheesecloth 

 curtains, and the sections were sub- 

 jected to various forms of experiment. 

 Some of the sections were sprayed 

 periodically with Bordeaux mixture; 

 some were sprayed with the Bordeaux 

 and also with ammoniacal copper car- 

 bonate. In two sections of each bench, 

 used as "checks," no fungicide was 

 applied, but overhead watering was 

 used in one of these sections, while in 

 the other the soil alone was watered. 



The results in house No. 1, says Mr. 

 Peltier, show that all the spraying 

 treatments were ineffective in the con- 

 trol of the rust. The largest amount 

 of infection naturally occurred in those 

 sections in which the plants were 

 watered from overhead. Where only the 

 soil in the sections was watered the 



The use of snapdragon cuttings or seedlings where 

 rust is present may mean a complete failure of the crop. 



Syringing is an important factor in the prevalence 

 of the rust in the greenhouse. It is a means of dis^ 

 semination of the spores, and it produces cq^ditions 

 favorable for the germination of the spores and the 

 rapid infection of the plants. 



which are the first indication of the 

 disease, do not become evident until 

 some time after infection has taken 

 place. Cuttings from such plants, carry- 

 ing the disease in the incipient stage, 

 may thus become centers of infection 

 for an entire bench of cuttings. 



Two important conditions favorable 

 to the development and dissemination 

 of the rust in a bench of cuttings are 

 shade and syringing. For a week or 

 ten days after the cuttings are placed 

 in the sand the usual, procedure is to 

 syringe the cuttings frequently and 

 keep them under shade in bright 

 weather. Such conditions are most fa- 

 vorable for the germination of the rust 

 spores in that the necessary degree of 

 moisture is maintained. The fungus 

 will mature rapidly, new spores will be 

 produced, and soon the entire lot of 

 cuttings will show infec- 

 tion. 



Syringing is practiced 

 also for the control of small 

 insects, such as the red 

 spider. When syringing is 

 practiced in an infected 

 house, the development and 

 spread of the rust are rapid. 

 Syringing, then, not only 

 favors the development of 

 the rust, but it actually 

 carries q^nd spreads the 

 spores to other plants. 

 Where no syringing is done, 

 the rust spores are less 

 likely to germinate, and 

 consequently less infection 

 results. 



Watering the plants from below only, so as to avoid 

 wetting the foliage, is a means of checking the rust. 



Snapdragon rust is not carried on the seeds. The 

 disease can therefore be avoided, or eliminated in time, 

 by the propagation of plants from seed. 



Habit of Plant. 



check better than by the use of fungi- 

 cides. 



Cuttings arc extremely susceptible to 

 rust, both in the cutting bench and 

 after they are potted. Mr. Peltier 

 states that he has seen 1^,000 cuttings 

 infected with rust and killed in three 

 weeks' time. He has also seen a large 

 number of young plants lost just after 

 being potted. Great care, therefore, 

 must be exercised, he says, to prevent 

 infection of cuttings. Such infection 

 may be initiated in the cutting bench 

 either by the introduction of spores or 

 by the use of cuttings made from in- 

 fected plants. A single diseased cut- 

 ting may mean the loss of nearly all 

 the cuttings later. It is extremely diffi- 

 cult to select cuttings free from the 

 disease in a house or field where the 

 rust has been prevalent. Certain 

 plants may appear to be free from rust, 

 Ijut cuttings from these plants may 

 lead to disappointment, for the pustules. 



The form of tlie plant is 

 an important factor in the 

 (lestructiveness of the rust. 

 The ideal plant should fork 

 low and not have more than 

 five or six stems. Such a 

 plant is less liable to de- 

 struction by the rust than 

 a bushy plant with dense 

 foliage. This, of course, is 

 true where syringing is 

 practiced. The reason is 

 obvious; the plant with few 

 stems growing out from the center will 

 dry off quickly after syringing, while 

 several days may be necessary for the 

 center of a bushy plant to dry out. As 

 the rust spores require from twenty-four 

 to forty-eight hours for germination, 

 the evaporation of the water during 

 the day will kill the germinating spores 

 and so prevent infection. Where the 

 water does not evaporate for several 

 days, rust will invariably develop. The 

 habit of the plant, then, is of some im- 

 portance in checking the spread of rust 

 in the greenhouse. 



An attempt to control the rust by 

 pinching off and destroying the in- 

 fected leaves was practically a total 

 failure, although partial success was 

 obtained during the winter months, 

 when the development and spread of 

 rust was slow. 



Experiments were also conducted in 

 an effort to determine whether rust can 

 be carried on the seed. Seed represent- 



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