52 ROOT-KNOT AND ITS CONTROL. 



gro\\ing condition and perhaps, therefore, less injured when the root 

 hairs were killed by the chemical. Further experiments on this line 

 should be carried out. 



FERTIXIZERS. 



It is the result of general observation that if trees affected by root- 

 knot can be forced into rapid growth, especially in the early part of 

 the season, so that the roots penetrate deeply into the ground and 

 form a widely branching system, they will thenceforward usually 

 develop normally and cease to show much injury from the nematode. 

 This is particularly the case with the peach. Many growers now on 

 setting out an orchard where the pest is present fertilize the trees 

 very higlily, so that they xnay start right into growth and keep ahead 

 of the nematode injury. As sho\vn on page 41, the nematodes are 

 mostly confined to the upper 12 to 16 inches of soil, so that if the 

 roots can be forced to grow rapidly and deeply enough they will 

 escape much injury. To accomplish this, it is necessary that the soil 

 be prepared to a good depth before setting out the trees and that an 

 abundance of nitrogenous fertilizers be given. The various potas- 

 sium salts, too, are apparently very beneficial in the Southeastern 

 States, so much so that some people believe that they destroy the 

 root-knot nematode. Perhaps in the naturally rather potash-poor 

 soils of many of the Southern States the addition of potassium is 

 simply another factor in bringing the plant to its normal resistant 

 power. At any rate, in the writer's experiments plants given an 

 excess of potash suffered less from root-knot than those not so fer- 

 tilized. It has been found in Germany that the sugar-beet nema- 

 tode removes the mineral salts from the roots about equally. If, 

 however, the soil is not much overstocked with potash it would be 

 exhausted in the plant sooner than the others, for, being less abundant 

 in the soil, it would be taken up less rapidly by the roots. The same 

 would be true of any other of the necessary minerals. This may 

 explain the effect of potash in combating this disease. 



FLOODING. 



In view of the fact that root-knot injurj^ never seems to be severe 

 in soils that are flooded for a part of each year it seemed reasonable 

 to suppose that flooding might have a beneficial effect when applied 

 to affected trees. Unfortunately, however, through a misunder- 

 standing of instructions the experiments arranged to be carried out on 

 this line failed to be performed. It is certain, however, that great 

 care must be taken, for many trees are killed by havmg their roots 

 submerged even a few days. 



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