50 BOOT-KNOT AND ITS CONTROL. 



soil outside of the disinfected patch can get to their roots. In deep 

 sandy soil the writer found not all the nematodes destroyed by the 

 use of 2 ounces of carbon bisulphid per square yard, but when 4 

 ounces were used they were exterminated. The size of the area to 

 be treated depends upon the size and rapidity of growth of the trees 

 to be planted, the faster they grow the smaller being the area to be 

 treated. For the best results the chemical must be placed at a depth 

 of several inches below the surface, the opening being firmly closed 

 so that the vapors will have to diffuse throughout the soil. In France 

 special forms of apparatus have been devised for this purpose in 

 combating phylloxera. They consist of a reservoir for the liquid and 

 a hollow rod which can be inserted to any desired depth, a measured 

 quantity of the liquid then being forced out into the soil. In the 

 writer's experiments, however, use was not made of these rather 

 expensive contrivances, but of a simple dibble consisting of a pointed 

 piece of broomstick. Holes were made to the depth of a foot to the 

 number of eight or nine to the square yard. The desired amount of 

 carbon bisulphid was poured into them, each being closed at once by 

 the foot and the earth firmly pressed down to prevent the escape of 

 the vapors into the air. About a teaspoonful to each hole is sufficient, 

 or about 4 ounces to the square yard. 



Potassium sulphocarhonate. — Potassium sulphocarbonate in the form 

 of a solution of 1 part, by weight, to 5 parts of water to be applied in 

 little trenches dug around the diseased trees is recommended by Gan- 

 dara.^ According to him, 4,000 liters of the solution suffice for a 

 hectare— i. e., about 425 gallons per acre. His experiments were with 

 nematode- affected coffee. This treatment he reports as being success- 

 ful, but too expensive for general use. The WTiter's results, however, 

 were not so successful. Papaya plants {Carica 'papaya), about 18 to 

 20 months old and with roots badly affected with root-knot, were used. 

 The chemical, diluted as directed by Gandara, was applied to some 

 trees in little ditches and to some in numerous holes about a foot deep. 

 After it had all soaked in, the soil was watered thoroughly, as it was 

 very dry, so that the chemical might the better soak evenly through 

 the soil. In a day or two some of the old leaves dropped, showing 

 that the roots had suffered some injury; but at the expiration of a 

 few weeks the roots were found to be as badly knotted as ever, prov- 

 ing that for the papaya, at least, this process is ineffective. The 

 high cost of the chemical, moreover, woul<l make its use utterly 

 impracticable. 



Formaldehyde. — In view of the comparative success obtained with 

 formaldehyde solution on roses it was tested on papaya trees out of 

 doors. A ridge of earth was made around each tree at a distance of 



» G&ndara, 1906. 

 217 



