BLIGHTS OF CONIFEROUS NURSERY STOCK. 5 



mixture, ammoniacal copper carbonate, and copper acetate were 

 tested repeatedly during several seasons. Unfortunately for the 

 experiments, little trouble with the disease occurred at the times 

 when the fungicides were used. In four cases, however, the disease 

 attacked parts of the nursery containing experimental plats which 

 had been more or less recently sprayed with copper mixtures con- 

 taining soap. In these cases there was no evidence that the fungi- 

 cides afforded any protection. This lessens the likelihood that needle 

 parasites are concerned in causing the disease. 



(2) On sandy soil the attacks which most closely imitate parasitic 

 injury by killing definite patches occur suddenly and often simul- 

 taneously in many parts of the nursery. Serious damage may appear 

 through thousands of square feet of seed beds inside of 48 hours 

 from the tin e the first evidence occurs. This renders it unlikely 

 that root parasites play any important part in causing the disease. 



(3) The most typical attacks of the disease observed at Halsey 

 occurred on days when wind and temperature were high and humidity 

 low and following nights which had been unusually warm and with- 

 out dew — conditions which favor excessive transpiration. This em- 

 phasizes the relation of transpiration to the disease. 



(4) In general, the most trouble occurs during dry seasons. The 

 larger commercial nurseries in Minnesota and Iowa report that the 

 most serious trouble they have had was during the very unusually 

 dry summer of 1910. 



(5) Partial shade greatly decreases loss and entirely prevents 

 trouble except in very severe attacks or during persistent drought. 

 Shade was tested in five different attacks at Halsey in 1908, 1909, and 

 1910, and in all cases controlled or greatly lessened the losses, as 

 indicated by the results in adjacent shaded and unshaded plats. 



(6) Crowding strongly predisposes to the trouble. In the beds at 

 Halsey the seedlings at the margins which have sent their roots out 

 into the unoccupied paths are practically never attacked, though in 

 some cases the entire interiors of beds have been killed. This im- 

 munity of the edges of the beds is more marked on sandy soils than 

 on heavier ones. 



(7) Attacks of the disease regularly occur when the soil is very 

 dry. Very sandy soils, which are more quickly reduced to a low 

 water content, are the commonest locations for the disease. In two 

 different attacks at Halsey direct comparisons were made of soil 

 moisture in diseased and relatively healthy areas, taking samples 

 between the depths of 7 and 11 inches, where the greatest mass of 

 absorbing roots lay. In one case the samples from the four points 

 tested in the healthy area showed an average water content 32 per 

 cent higher than that of the two points taken in the blighted stand 

 adjacent-. At the time of the other attack four samples were taken 



