26 BULLETIN 453, U. S. DEPARTMENT OF AGRICULTURE. 



Middle West, where the acid in single-season tests did not give as 

 good results as other substances, there is reason to believe that the 

 results of the acid treatment will be much better in normal seasons. 

 The acid has to recommend it, in addition to its effectiveness against 

 damping-off, the elements of cheapness, efficiency in killing weeds, 

 and in many places of causing an increased growth of the conifers. 



Copper sulphate, tested at 11 different places, gave no indica- 

 tions of value at three of them and very doubtful indications at the 

 fourth. At the others it gave more or less indication of value, reaching 

 the stage of regular nursery use at one nursery and at two others giving 

 better results than the acid in single-season tests. Copper-sulphate 

 treatment costs about the same as treatment with acid and is nearly 

 or quite as effective in killing weeds, but has not been observed to 

 result in any marked increase in growth of the conifers. 



Data as to the value of zinc chlorid were secured from ten nur- 

 series. At one of these it failed. At three others the tests were very 

 preliminary, and while value was indicated the extent of value was 

 not determined. At four it indicated value, but to a less extent 

 than other treatments used. At the remaining two it indicated 

 sufficient value to rank as a successful treatment. At both of the 

 nurseries where it has been given repeated tests it has proved as 

 good as any other treatment. At both of these, however, it has not 

 been shown to be decidedly better than cheaper treatments (copper 

 sulphate at Garden City and sulphuric acid at Fort Bayard), and 

 therefore is not likely to replace them in regular use. Like copper 

 sulphate, it kills weeds in addition to decreasing damping-off and 

 has not been observed to cause increased growth of the conifers. 

 The relatively high cost of this disinfectant, approximately one-half 

 cent per square foot on heavy soils for material alone, is a point 

 against it. Both copper sulphate and zinc chlorid cause injury to 

 pines on some soils where acid seems entirely harmless. This means 

 that their use will at most places necessitate more watering during 

 the germinating period than is necessary when acid is used. 



Data as to the value of formaldehyde in controlling damping-off 

 have been secured from 12 places. At two of these it has failed. 

 At another it has indicated value; extent undetermined. At five 

 others it has indicated less value than sulphuric acid, while at the 

 four remaining places it has been reported as successful. 1 It also 

 kills weeds, has little effect on the growth of pines, and has the 

 advantage of never making necessary any extra watering in treated 

 plats. The points against it, in addition to its inferior efficiency in 

 controlling damping-off at many nurseries, are its high cost and its 

 tendency to kill seed if applied at or near the time of sowing. It is 



1 At Dundee, formaldehyde alone was considered a failure, as the only successful formaldehyde plats 

 were those also treated with zinc chlorid. 



