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



ered was approximately $7.60 per 1,000 square feet; that for the season 

 of 1912 the cost in the acid beds was $5.40 less than in the untreated 

 beds; and in 1913, $5.20 less. This saving in cost of weeding exceeds 

 the entire cost of the acid treatment as estimated during the first of 

 these years. While the net value of weed control will not be as great 

 as this in all seasons or at all nurseries, it appears that at several of 

 the nurseries where tests have been carried on the benefit from weed 

 control (PL II, fig. 2) or from increased growth of the seedlings, or 

 from both of these effects combined, will be sufficient to more than 

 justify the treatment. In such cases the control of damping-off 

 secured by the treatments will be clear gain. It is especially inter- 

 esting to note that in the seed beds of the Feather River Forest 

 Experiment Station (California) a light sulphuric-acid treatment is in 

 regular "use simply on account of its value as a weed killer, entirely 

 irrespective of any effect on damping-off. 



CONCLUSIONS AS TO SOIL DISINFECTANTS. 



The results listed in Table III indicate the complexity of the 

 problem of soil treatment to control damping-off parasites. It is 

 at once evident that a single season's experiments conducted on a 

 single soil do not furnish a basis on which it is safe to make recom- 

 mendations for general use. It furthermore appears that even after 

 as extensive experiments as are here reported, it is not possible to 

 prescribe any one treatment which will be safe and effective at all 

 nurseries. Heat, the disinfecting agent most commonly employed 

 by workers with truck soils, has proved inferior to other methods at all 

 of the nurseries at which it has been tried. Sulphur, which is re- 

 ported to have given excellent results against certain root diseases of 

 other plants, has on the whole given disappointing results in pine 

 seed beds. Formaldehyde, sulphuric acid, copper sulphate, and zinc 

 chlorid, the four most generally satisfactory substances, have each 

 failed at one or more nurseries. Especially at nurseries where no 

 adequate watering system has been installed the frequent watering 

 which beds treated with acid or with copper and zinc salts sometimes 

 require means considerable trouble and expense. 



However, after all these difficulties and drawbacks have been con- 

 sidered, analysis of the results indicates that it will be practicable to 

 control damping-off by some soil treatment at any nursery where it 

 is troublesome. The first part of Table III, containing results at the 

 seven nurseries where repeated tests have been made, is, of course, 

 the most important. At all of these nurseries soil treatment has 

 proved successful. It is significant that at all but one of these seven 

 sulphuric acid has proved successful. The acid failed at the seventh 

 nursery only because of the high carbonate content of the soil, a con- 

 dition rarely foimd at coniferous nurseries. At this seventh nursery 



