74 ROOT-KNOT AND ITS CONTROL. 



sometimes brought to a field in mamire if the mamire pile has stood 

 on infested soil. 



(6) The folloAving methods of control in greenhouses and seed beds 

 may be used: (a) The most efficient method is the use of live steam 

 at fairly high pressure. The steam is forced through a s3^stem of per- 

 forated pipes laid at the bottom of the bed or bench, (h) The old 

 infested soil may be entirely removed and the benches thoroughly 

 cleaned out. Then noninfected soil may be put in its place. This 

 method is not advisable in regions where the nematode occurs out 

 of doors in the vicinity, (c) Infected soil, when it is desired to save 

 it and steaming is impracticable, may be freed by allowing it to he 

 through the winter in a place where it vnW be exposed to alternate 

 freezmg and thawing, and especially to drying, (d) Soil containmg 

 perennial plants can be nearly if not quite freed from nematodes by 

 the use of an abundance of a solution of formaldehyde (1 part of com- 

 mercial formaldehyde to 100 parts of water). This solution is fatal 

 to many plants and can be used only with great caution. 



(7) For the control of the nematode in the field where the land is 

 occupied by perennial crops no entirely satisfactory chemical applica- 

 tion can be recommended. Places where trees are to be reset should 

 be freed from nematodes by the use of carbon bisulphid at a rate of 

 3 or 4 ounces per square yard placed in about nine holes per square 

 yard, these holes being about 6 to 12 inches deep and to be filled vnih 

 dirt as soon as the chemical is placed in them. Carbon bisulphid can 

 not be used with safety around living trees. Flooding the land seems 

 to be- unsatisfactory, as flooding long enough to kill the nematodes 

 is usually fatal to the trees. High fertilization and constant culti- 

 vation to induce growth often so help the trees that they are able, as 

 it seems, to outgrow the trouble, the roots either penetrating to 

 levels where the nematodes are less abundant or being formed faster 

 than the galls can be produced. Avoid growing susceptible cover 

 crops, like the ordinary nonresistant varieties of cowpeas, for exam- 

 ple, for these multiply the nematodes in the soil manyfold. In pre- 

 paring the land for setting out a perennial crop the soil should be 

 freed from nematodes by the use of the methods suggested below. 



(8) For land infested with nematodes and not bearing a perennial 

 crop, the following methods may be recommended: (a) Keeping 

 the land free from vegetation of all kinds for two years. Tliis is 

 the most eff'ective method, but it is not practicable in many cases. 

 (6) Planting the land to nonsusceptible crops for at least two (perhaps 

 better three) years, using in the winter small grains, such as wheat, 

 rye, or oats, and in the summer the velvet bean, Florida beggarweed, 

 the Iron cowpea, or even peanuts, scrupulously destro3dng all weeds 

 that might harbor the nematodes, (c) Making heavy applications of 



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