26 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



weather resulted in a long germination period, it has killed or in- 

 hibited the germination of some of the dormant seed. All injury 

 can be prevented by treatment a few days before sowing, followed 

 by the addition of lime just before sowing, but lime used in this 

 way has apparently destroyed a considerable part of the value of the 

 acid treatment against the disease. Further consideration of the 

 data on which earlier papers (63, 67) were based indicates that the 

 apparent need for frequent watering during the germination period, 

 which was required at a few of the nurseries where the first tests of 

 acid treatment were made, as well as practically all of the germina- 

 tion reduction, was due to the use of unnecessarily large applications 

 of acid and that the trouble can be eliminated by determining by 

 test the minimum quantity of acid which will be reasonably effective 

 in each locality. If this can be done it should establish the acid 

 treatment as the most profitable for general use of any of the 

 methods of damping-off control which have so far been extensively 

 tested. 



In view of the various parasites which may cause damping-off at 

 different times and places and which vary greatly both in their 

 means of dissemination and in their physiological qualities, it is not 

 believed that any single disinfectant will be found entirely satisfac- 

 tory at all nurseries. It is also unfortunately true that no one 

 strength of treatment can be recommended for all nurseries. The 

 quantity of acid to be used at any specified nursery will have to be 

 determined by test at that nursery. A single test, no matter how 

 well conducted, is not sufficient to serve as a basis for conclusions. 

 However, a number of small-scale tests, made at different times and 

 in different parts of the seed-bed area, should determine the best 

 treatment for any particular nursery with a reasonable degree of 

 certainty and with very little work. If the plats are equal in size 

 and receive equal quantities of seed, all the nurseryman needs to do 

 to determine the value of the treatments is to count the number of 

 living seedlings on the different plats at the end of the season. The 

 decrease in the number of weeds as a result of the use of acid is 

 itself sufficient at a number of nurseries to pay the entire cost of the 

 treatment. Detailed methods of application have already been pub- 

 lished (67). The differing proportions of acid between which the 

 best treatment will ordinarily be found to lie are 2 and 7 c. c. (one- 

 sixteenth and one-fourth of a fluid ounce) of the concentrated com- 

 mercial acid per square foot of seed bed, applied just after the seed is 

 sown and covered. It should be dissolved in 500 to 1,000 c. c. (1 to 2 

 pints) of water per square foot of bed before applying. The drier 

 the soil before treatment, the more water should be used in dissolving 

 the acid. 



No treatment applied after germination begins can have the maxi- 

 mum value in controlling the disease, because the damping-off para- 



