DAMPING-OFF OF CONIFEROUS SEEDLINGS. 11 



Copper sulphate could probably have been used with success in 

 quantities less than one-fourth ounce per square foot. A three-eighths 

 ounce zinc-chlorid treatment proved unsuccessful. Both disinfect- 

 ants were dissolved in water and applied in most cases just after seed 

 sowing, as was done with acid. Both were found harmless to the 

 dormant seed in these concentrations, but both were capable of 

 injuring germinating seedlings in just the same way as is described 

 for acid at Halsey. This injury was prevented by extra watering 

 during the germinating period, in the same way as acid injury was 

 prevented at the Halsey and Kansas sand-hill nurseries. The 

 amount of this extra watering needed at the Garden City nursery was 

 very slight. 



An interesting thing that developed at this nursery, as well as at 

 the Kansas sand-hill nursery, was the control of spring damping-off 

 by treatments applied during November of the preceding year. Part 

 of the fall-sown plats whose results were shown in Table II were 

 treated at the time of sowing and part as soon as the soil thawed the 

 following spring. Though the seedlings did not appear until the 

 following April, disinfectants applied in November seemed to protect 

 them from damping-off as well, or practically as well, as disinfectants 

 applied in March. At this nursery and at the five preceding at which 

 repeated tests were made, the treatments developed have been put 

 into regular large-scale use by the nurserymen, with good results. 



RESULTS OF SOIL DISINFECTION AT NURSERIES WHERE TESTS HAVE BEEN LIMITED 



• TO A SINGLE SEASON. 



At Porvenir, N. Mex., Dundee, 111., Lincoln, Nebr., the nursery of 

 the State Board of Forestry hi Vilas County, Wis., and the greenhouses 

 of the United States Department of Agriculture at Washington, D. C, 

 single-season tests of sulphuric acid have given good results. At all 

 of these places no need was found for any special watering provision for 

 the prevention of chemical injury from the acid. The tests at 

 Dundee and Lincoln were made during an unusually rainy season. 

 It may develop that in years with less rain more watering will be 

 needed at these places. 



At four other nurseries where disinfectants were tested in this pre- 

 liminary way the results were less definite. At Morrisville, Pa., 

 already referred to, there was distinct evidence that a very weak acid 

 treatment with sufficient watering during the germinating period will 

 be entirely successful in controlling the small amount of damping-off 

 which normally occurs there. One-eighth ounce of acid per square foot 

 it is thought will be sufficient. Insufficient watering prevented the 

 securing of exact information from the tests conducted. At Poca- 

 tello, Idaho, a single test of acid on beds of Douglas fir had no con- 

 spicuous effect on the amount of damping-off. As the soil is found 

 to effervesce on the addition of acid, success with acid does not 



