46 ROOT-KNOT AND ITS CONTROL. 



framework of the beds sJiould be thorouo:hly whitewashed with strong, 

 hot whitewash, freslily made from good qiiickUme, or it may be 

 painted with formaldehyde or some other disinfectant of this nature. 

 This is to kill all larvae or eggs that might be in the dirt adhering to 

 the cracks. In selecting new soil it will always be well to examine 

 the roots of susceptible plants growing where the soil is to be obtained 

 in order to determine whether or not root-knot is present. This 

 method has given good satisfaction where carried out in the North. 

 It is applicable, however, only to small greenhouses that do not 

 require much new soil. Large greenhouses can be far better taken 

 care of by sterilizing the soil in the benches. 



It often happens that to obtain fresh soil is not desirable in view 

 of the character of the soil in the vicinity. Perhaps it has taken 

 some years to bring up the soil in the beds to the desired lightness, 

 humus content, etc., and to have to take new soil every year would 

 be a hardship. In such cases steaming should be made use of if pos- 

 sible. If it is not feasible, a formaldehyde solution has shown itself 

 of considerable value. 



PORMALDEH^TtE . 



The formaldehyde method consists essentially of treating the soil 

 with a weak solution of commercial formaldehyde (or formalin). It 

 has been found that a solution of 1 part commercial (36 to 40 per cent) 

 formaldehyde in 100 parts water is effective against the root-knot 

 nematode in shallow beds when applied at the rate of 1 to 1 J gallons 

 (or more in the case of very absorbent soils) to every square yard of 

 soil surface. For deep beds the quantity must be increased. Care 

 must be taken that all parts of the soil are reached and thoroughly 

 wetted by the solution. Upon the thoroughness with which it is done 

 depends largely the success of the process. After the formaldehyde 

 solution has soaked in the soil should be thoroughly stirred, so that 

 all parts may be exposed to the disinfectant. Before setting into the 

 soil any plants or sowing any seeds the excess of formaldehyde must 

 be allowed to escape by evaporation or, if necessary, be washed out by 

 flooding the bed. The former is preferable. The writer has not found 

 the germination of seeds interfered with when 10 davs are allowed to 

 elapse between the treatment and the sowing of the seeds, especially 

 if the soil be allowed to become rather dry and be stirred in the mean- 

 while. 



This formaldehyde treatment has been used with success at the 

 Ohio Agricultural Experiment Station ^ in the forcing house and seed 

 beds. It was applied primarily to prevent certain damping-off fungi 

 from destroying the seedlings, but it was found that the nematodes 

 were sometimes destroyed also or greatly reduced in numbers. How- 



> Selby, 1906. 

 217 



