CONTROL OF ROOT-KNOT. 53 



CONTROL OF ROOT-KNOT IN THE FIELD WHEN NO CROP IS PRESENT. 



Land known to contain the root-knot nematode and not occupied 

 by a permanent crop like an orchard, grove, etc., may be freed from 

 the pest far more readily than land so occupied. The methods are 

 the same, whether the land is to be planted subsequently to annual 

 crops or to trees. The only difference is that land destined for 

 perennial crops must be more thoroughly cleared of the root-knot 

 nematode than that destined for simply one-year crops. 



CHEMICALS. 



Carbon hisulphid. — Carbon bisulphid is undoubtedly the most 

 efficient chemical for the destruction of the nematode in fields. 

 Experiments were made by the writer at Monetta, S. C, in 1906 and 

 repeated in 1907, which showed that when used as previously described 

 at the rate of 4 ounces per square yard of surface the nematodes were 

 practically exterminated, being found only at the edges of the plats, 

 where they could have come in from the surrounding untreated land. 

 Two ounces per square yard did not prove so effective, although the 

 nematodes were largely destroyed by even this application. In 

 view, however, of the quantity required and of the high price of this 

 chemical it is very evidently out of the question to a})ply it on a 

 large scale. Even in bulk the crude carbon bisulphid costs 10 to 

 15 cents a pound. At 4 ounces a square yard the cost for an acre, 

 not including cost of the labor required, would be from $120 to $180. 

 Nearly all the chemicals that have been suggested have the same 

 fault. Yet for small patches when it is desired, perhaps, to destroy 

 the nematode where a tree is to be set out, or in a small spot where 

 the pest has appeared but has not spread badly, it would probably 

 be found very effective. 



Formaldehyde. — Formaldehyde was tested at Monetta, S. C, in 

 both 1906 and 1907, and at Miami, Fla., as well, in 1906. It was apphed 

 as a solution of 1 part commercial formaldehyde (36 to 40 per cent) 

 in 100 or 200 parts of water. The solution was either sprinkled directly 

 on the surface or poured into deep furrows, which were leveled off after 

 the solution had soaked in. From 1 to 2 gallons per square yard of 

 surface were used. As a whole, the treatment did not recommend 

 itself. In no case were the nematodes entirely destroyed, although 

 they were considerably reduced in numbers. The plants gro%\Ti on 

 these plats after the treatment showed the presence of root-knot 

 galls on their deeper roots, although most of the upper layer of soil 

 seemed to be free from the pest. This would indicate that a larger 

 quantity would perhaps penetrate deeply enough to kill all the 

 nematodes in the soil. With formaldehyde at 20 cents a j)ound, 

 wholesale, the cost of treating an acre with the stronger solution, 



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