20 MASS. EXPERIMENT STATION BULLETIN 398 



growth in the acid than in the slightly alkaline soil. Dichromates usually gave 

 somewhat more complete protection and, if used in unnecessarily heavy applica- 

 tions, retarded growth of seedlings more than did the chromates. But if applied 

 at the time of seeding and at the rate of not more than 0.45. gm. per square foot, 

 the chromates and dichromates of potassium, sodium, and ammonium were 

 without ill effect on cucumber, beet, chard, pea, and bean; and the chromates of 

 potassium and ammonium, especially the latter, gave very good results. Potas- 

 sium dichromate was most effective and safe when applied to soil immediately 

 after seeding. Applied 24 hours later, it retarded germination of seeds of some 

 species. It gave satisfactory control when applied to soil two weeks before seed- 

 ing but was less effective when applied more than three weeks before seeding. 

 Chromate and dichromate of potassium, as used, gave more complete protection 

 than did the corresponding salts of sodium. Chromic acid gave superior results 

 only with beet; and the chloride, nitrate, and sulfate of chromium were almost 

 completely ineffective. 



Cresol, in as light an application as L5 cc. per square foot, immediately after 

 seeding, gave good control, almost as good as did formaldehyde. 



A very light application of formaldehyde (4.9 cc. or one teaspoonful per gallon 

 of water) was most effective when applied to soil immediately after seeding, de- 

 cidedly less effective when applied more than 24 hours after seeding. Growth of 

 beet, cucumber, and lettuce was improved by applications made not more than 

 8 hours after seeding, but seedlings of pea were injured when the first application 

 was made 24 hours after seeding. 



When nutrients in the form of potassium nitrate and precipitated bone or 

 Ammo-Phos were added to a solution of formaldehyde and applied to soil at the 

 time of seeding, the fungicidal action of the formaldehyde was unimpaired. But 

 in a good sandy loam, the growth of seedlings of pepper, eggplant, beet, and cu- 

 cumber was improved as much by formaldehj'de alone as by formaldehyde plus 

 the nutrients. 



Starter solutions applied to the soil around tomato plants as they are set in the 

 field cannot, w'thout danger of chemical injury to the plants, carry enough for- 

 maldehyde to be effective against soil fungi. 



Lacking chemicals, seeds of some kinds, not all, may well be sown on a layer of 

 sphagnum, overlying soil. Damping-off was well controlled in this way, although 

 not so completely as by formaldehyde treatment of soil. Sphagnum so used gave 

 good results with lettuce, cabbage, and cress, the two latter being especially 

 susceptible to injury by formaldehyde; but sphagnum did not give good results 

 as regards either stands or growth of the solanaceous plants, pepper, eggplant, 

 and tobacco. 



Chemical Soil Surface Treatments in Hotbeds for Controlling Damping-off 

 of Early Forcing Vegetables. (W. L. Doran, E. F. Guba, and C. J. Gilgut.) 

 This study w^as completed with the publication of Bulletin 394. 



In some additional tests, certain newer chemical materials offered as seed pro- 

 tectants, notably Spergon, Thiosan, yellow cuprous oxide, and tri-basic copper 

 sulfate, showed in many instances value equal to or surpassing Semesan, red Cu- 

 prous oxide, and zinc oxide on a wide variety of flower and vegetable seeds. 



Control of Greenhouse Vegetable Diseases. (E. F. Guba, Waltham.) The 

 various types of tomatoes studied for their reaction to Alternaria early blight 

 were also tested for their susceptibility to Cladosporium leaf mold. Among them 

 seven types were found showing a very slight degree of susceptibility indicated by 

 sparse, yellowish areas without sporulation, molding, or necrosis, and one type 

 showing none of these symptoms and from all appearances immune. In addition. 



