556 THE MONTHLY BULLETIN. 



pieces of fibrous roots, the size and length of a common pin. It 

 seemed to me that if this condition existed throughout the fibrous root 

 system it would be sufficient liurden on the tree to cause yellowing of 

 the leaf irrespective of other influences that might be at work on the 

 tree. 



I reported the matter to Mr. Meserve, and later to Mr. William 

 Wood, the present horticultural commissioner of Los Angeles County, 

 who encouraged me to go on with the work. I have at various times 

 reported the work to professional horticulturists, from whom very 

 little encouragement has been received, until Mr. E. E. Thomas^ of the 

 Whittier Laboratory, followed up the matter and published a circular 

 on the subject. I wish to thank Mr. Thomas for his interest in the 

 matter, notwithstanding the fact that the problem will be worth very 

 little to me, but might be worth something to him. 



I believe that nematodes often infest the roots of nursery stock that 

 are transplanted in the orchard and that they spread from one tree 

 to another in the irrigation and storm water. I have kept these 

 nematode worms for eight days in water without apparent injury. In 

 badly infested orchards they appear to infest the roots of the vetch, 

 malva and other weeds, sometimes to the extent of killing out the 

 vetch and malva. They apparently make little headway on the alfilaria. 

 I have had some success in treating afi^ected trees with carbon 

 bisulphide. The best results were obtained by making shallow holes 

 about two inches deep, one foot apart each way, and putting about 

 three fourths of an ounce of carbon bisulphide in each hole and cov- 

 ering the ground with an impervious tent or cloth and allowing it to 

 remain for about forty-eight hours before removal. After treating 

 the ground with this dosage no live nematodes could be found. Just 

 how much smaller dosage could be used with success I do not know. 

 Trees treated with greater amounts than this showed injury and lost 

 their leaves. After treating, the ground was covered with a mulch of 

 barnyard manure, about one inch thick, which kept up an even moisture 

 content of about ten per cent during the season following. The trees 

 now show a normal condition of fibrous roots, but are not entirely 

 free from the nematode. The pest, however, is so far eliminated that 

 the trees are doing well. 



I think that mottled leaf and the "small off" is due to the large 

 numbers of the pest that infests the roots. Just as with other pests, 

 as for example the red spider, a small number will do no apparent 

 injury, while a large increase in numbers will cut down the produc- 

 tiveness of the tree to a great extent. 



'A preliminary report of a nematode observed on citrus roots and its possible 

 relation with the mottled appearance of citrus trees. — Circular 85, Cal. Agrcl. Exp. 

 Station, Feb., 1913. 



