Onion Smut in Indiana 319 



shrinkage in storage of the onions grown in infested fields is very much 

 greater than in those from uninfested fields or from formaldehyde 

 treated seed. 



It has been proven beyond a doubt that the formaldehyde "drip" 

 method of treatment will control the onion smut very effectively but the 

 method was designed to apply to onions that are sown at the rate of 

 five to seven pounds per acre. In Lake County, where the seed is 

 sown at the rate of about 60 pounds per acre, the problem is somewhat 

 different. Under these conditions the control is never 100 per cent but 

 it has been sufficiently effective to secure its adoption by the majority 

 of growers. The probable explanation of the control by the formalde- 

 hyde treatment is that the gas evolved disinfects the soil in the immedi- 

 ate vicinity of the seed through which the seedlings must grow thus 

 killing the spores or the saprophytic mycelium. This disinfecting action 

 does not seem to extend over a sufficient area to permit the large num- 

 ber of seedlings developed in the row to grow in disinfected soil and 

 as a result a small proportion of the plants may be diseased. This may 

 possibly be explained by the fact that the formaldehyde does not wet 

 an area more than three-quarters of an inch wide, though the gas may 

 spread somewhat beyond this, whereas the row of onion seedlings is 

 about an inch and a quarter wide. 



Aside from the failure of the formaldehyde to completely disinfect 

 the soil there are other factors that seem to affect the efficiency of the 

 treatment. The growers believe that spring plowing so loosens the soil 

 that the formaldehyde penetrates too deeply for proper or sufficient dis- 

 infection. The amount of rain at planting time and immediately fol- 

 lowing is very important. In 1921 the heavy continuous rains at the 

 time of treatment, and during the week following, practically nullified 

 all the beneficial effects. The probable explanation of this fact is that 

 the rain diluted the disinfectant so that it lost its potency, or else the 

 presence of the water in the soil prevented uniform penetration. 



The usual recommendation for dilution is one pint of 40 per cent 

 formaldehyde in 16 gallons of water, to be used at the rate of 200 gallons 

 per acre. 



The treated onions had about five per cent of smut while the un- 

 treated parts of the beds averaged about 50 per cent. Increases in yields 

 of 100 bushels per acre were obtained. 



The growers at Munster found that they were usually applying 

 only 140 to 160 gallons so it was decided to dilute the formaldehyde, 

 one pint in 10, 12, and 14 gallons of water. This was done in 1922 with 

 somewhat better control of the smut and without causing any injury 

 to the seedlings. Rather peculiar results were obtained, however, from 

 the treatment. The soil at the time of sowing was dry and the weather 

 very favorable for the treatment. An examination of the fields in June 

 showed the treated rows had less than five per cent of smut while the 

 untreated rows had as much as 95 per cent in some cases. In one field 

 where the grower did not use the treatment, over half of the plants 

 were being destroyed by the smut. During the summer there were no 

 effective rains and the temperature was generally above normal. These 



