32 MASS. EXPERIMENT STATION BULLETIN 351 



Copper -lime Dust 



An English recommendation which is mentioned by Newhall and his asso- 

 ciates (70) calls for about 22 gm. (per square foot) of a 10-90 copper-lime dust. 

 This is equal, on basis of copper content, to about 11 gm. of a 20-80 dust, which 

 was used in these experiments. Such an application did not prove heavy enough, 

 for less than 20 gm. of the 20-80 dust did not give satisfactory control of damping- 

 ofif. Control was usually good with 25 and 30 gm., not so good with 20 gm. 



Applications up to 30 gm. did not interfere with the germination of seeds of 

 Anemone coronaria, Delphinium, Salpiglossis, hollyhock, mignonette, and 

 Lilium teniiifolium and, by the prevention of some pre-emergence damping-ofT, 

 often improved it. Statice and sweet pea, however, were injured by 20 gm., 

 beet and cucumber by 25 gm., and hollyhock and mignonette were the only 

 species not injured by 30 gm. 



When efTects on both damping-off and growth of seedlings are consiaered, 

 copper-lime dust gave as good results as did any copper fungicide. Its use, in 

 quantities really effective against damping-off, would, however, have to be 

 limited to those species of plants which are least susceptible to chemical injury 

 by it. It makes soil less acid, and an application of 25 gm. to soil with an initial 

 pH value of 6.5 resulted in a pH value of 6.8 eight weeks later. For this reason, 

 copper-lime dust would not be indicated for use with species known to prefer 

 a more acid soil. 



With copper-lime dust as with the copper salts above mentioned, the greater 

 tolerance of hollyhock was evident. It is of interest in this connection that Eriks- 

 son (34) reported no injury to hollyhock growing in soil which he watered with a 

 0.3 percent solution of copper sulfate, for, if such watering was long continued, 

 there must have been a considerable accumulation of copper in the soil about the 

 roots of the plants. Cotton, another member of the Malvaceae, may be tolerant 

 of copper also, for in the work of Fikry (35), cotton plants were not injured by a 

 heavy application of copper sulfate to the soil in which they grew. 



Copper Oxalate 



Copper salts, in spite of the limitations above mentioned, may sometimes be 

 useful in protecting against Pythium the seeds and seedlings of such species as 

 germinate so slowly that a volatile chemical would be gone from the soil long 

 before protection was most needed. Copper oxalate, 6 gm., was applied to soil 

 immediately before sowing seeds of the umbrella pine. They germinated 3 months 

 later. Damping-ofT was well controlled, without chemical injury, and the stand 

 was increased nearly nine-fold compared with the checks, while there was little 

 if any benefit from acetic acid. Quick (74) has used copper oxalate similarly and 

 successfully as a soil fungicide for the protection of seeds of Ribes roezlii Reg. 

 during their stratification. 



Mercuric Chloride 



Mercury salts are apparently more effective against Rhizoctonia in the soil 

 than are copper salts; but mercury salts may be just as injurious to plants, and 

 it is important to know the quantities which may be expected to be effective 

 against fungi and at the same time safe to use. 



In the experiments of Jackson (51), China asters were protected against Fusa- 

 rium wilt by "soaking" the soil with a 0.1 percent solution and there was no 

 chemical injury. One quart of such solution contains about 0.95 gm. of the salt 





