16 MASS. EXPERIMENT STATION BULLETIN 394 



tions. It is evident that very light applications may be effective, but even 1.5 

 to 2.5 cc. are light applications compared with those commonly used in the past. 

 Growers should follow the suggestions made in Table 1 1 unless formaldehyde is 

 difficult to obtain in the amount desired. In that case, lighter applications, down 

 to about 1.0 cc. per square foot, may be made with the expectation that, even if 

 damping-off is not eliminated, at least its severity will be materially reduced. 



The application of formaldehyde after seeding is an effective and, except with 

 crucifers, a safe method of preventing damping-off. It is also convenient, for 

 water must usually be applied at this time anyway. There are, however, a few 

 simple precautions to be remembered. Soil so treated should not be covered, 

 as with burlap, or the formaldehyde fumes may.be held in the soil long enough 

 and in sufficient concentration to injure seeds. Seeds shculd not be soaked in 

 water before planting, for soaking makes them more susceptible to injury by 

 formaldehyde used in this way. Very cold water, water at a temperature below 

 50° F., ought not to be used in preparing the solutions of formaldehyde. A colder 

 soil delays both germination and the release of formaldehyde fumes. Formalde- 

 hyde in very cold water kills damping-off fungi but, for the reasons above stated, 

 it is more dangerous to seeds. 



It should be understood, of course, that onh' soil treatment with formaldehyde 

 or seed tieatment, not both, is to be used. 



Soil reaction does not appear to have an important effect on the efficacy of 

 formaldehyde used in this way. When formaldehyde (2 cc. in 1 quart water per 

 square foot) was applied to soil the pH value of which had been earlier adjusted 

 with hydrated lime, damping-ofT of beet, cucumber, and lettuce was equally well 

 controlled in soils having pH values of 5.5, 5.9, 6.1, and 7.0. 



It is interesting to note in this connection that, although soil acidit> is not a 

 sufficiently important factor affecting damping-off to make the disease ordinarily 

 ctntrcllab'e by the adjustment of soil reaction (4, 15), damping-off was usually 

 less severe in limed than in unlimed soil. Each line, horizontally in Table 15 

 represents a separate experiment. Soils without lime had pH values cf 5.9 to 6.1. 

 The same soils after treatmer t with hydrated lime had pH values of 7.0 to 7.2. 

 Damping-off was by no means entirely prevented by liming, but the average num- 

 ber of plants which lived was greater in limed soils than in unlimed soils by 51 

 percent in the case of beet, 163 peicent in the case of cress, and 258 percent in the 

 case of cucumber. 



Table 15. — Stands and Damping-off as Affected by Liming of Soil 



As is well known, the application o* formaldehyde to soil, in quantities sufficient 

 to be fungicidal but not injurious, often results in improved growth of plants. 

 That was true in many cf the experiments referred to above. With the object 

 of determining whether or not formaldehyde also improves growth if applied to 



