Apr. 29, 1918 



Stemphyliwm Leafspot of Cucumbers 



305 



CONTROL OF THE FUNGUS 



Certain preliminary experiments give promise that this disease may 

 be easily controlled by spraying the leaves with Bordeaux mixture. 



In the laboratory the slides were sprayed in the manner outlined by 

 Wallace, Blodgett, and Hesler.^ The method was as follows: One end 

 of a glass slide was sprayed with the spray mixture, and after drying, 

 the slide was supported on glass slips in a petri dish. A suspension of 

 spores in water evenly distributed by filtering through silk bolting cloth 

 was placed on both the sprayed and unsprayed ends of the slide. In 

 Table II is given the percentage of germination from the various treat- 

 ments. 



Table II. — Percentage of the spore germination of Stemphylium cucurbitacearum on 

 slides after spraying with Bordeaux mixture 



In each case the figures given represent the average of three slides. 

 Germination is recorded regardless of whether the germ tube was long 

 or short. In many cases, especially where the higher strengths of 

 Bordeaux mixture were used, the germ tubes Avere so short that infection 

 could hardly have taken place. For example, on the slides sprayed with 

 Bordeaux mixture 1-2-50 the germ tube averaged about 40 n, while 

 on the controls they were several hundred microns in length. Conse- 

 quently the figures given in Table II may underestimate rather than 

 overestimate the value of the spray mixture, provided the leaves are 

 thoroughly and evenly coated. To judge from the results given in 

 Table II, Bordeaux mixture 3-6-50 would appear to be entirely efficient 

 against this disease. 



To test this point further, four plants were sprayed with Bordeaux 

 mixture 2-4-50 and 3-6-50, respectivel}^ The next day these plants 

 were inoculated with a suspension of spores from a potato-glucose-agar 

 culture. Four plants sprayed with water were inoculated as controls. 

 Two small spots developed on the plants sprayed with Bordeaux mix- 

 ture 2-4-50, the other plants sprayed wnth the mixture remaining healthy. 

 The control plants developed numerous infections. 



> Wallace, Errett, Blodgett, F. M., and Hesler, L. R. studies of the fungicidal value op 

 UME-suLPHUR PREPARATIONS. N. Y. Cornell Agr. £xp. Sta. Bui. igo, p. 167-174. 1911. 



41815°— 18 4 



