FREEING A FIELD FROM ROOT-KNOT. 69 



(liiced on the few weeds whose presence it was unpossible absolutely 

 to prevent in the coM^eas. Thus, the weed known as careless weed 

 {Amaranthus sp.) was found to have root-knot in the field of Iron 

 cowpeas the second season these were grown. 



^Ir. Jackson also made the experiment of using summer fallow in 

 combination with winter rye, as follows: The preceding crop was 

 taken off the summer of 1906, being badly knotted. The field was 

 then kept in bare fallow from August, 1906, until the fall of 1907, 

 when it was sown to rye. This was turned under when about mature, 

 and in July, 1908, the field was sown to tomatoes (which are especially 

 susceptible to root-knot). A fine crop of tomatoes resulted, the 

 only nematodes present being in a small part of the field where Irish 

 potatoes were badly attacked in 1906 and where volunteer potatoes 

 came up in 1907. The remainder of the field remained free tlie 

 succeeding year also (1909). 



Prof. P. H. Rolfs * recommends letting the field grow up to crab- 

 grass (Syntherisma sanguinalis) after the crops are removed, first 

 taldng up and burning or otherwise destroying the plants to avoid 

 infection from them. According to him this method when used even 

 for only one year greatly reduces the number of nematodes present. 

 Dr. Neal ^ recommended the use of beggarweed, Japan clover, or 

 Mexican clover. Regarding the latter the present writer knows 

 nothing, but the first two are practically, if not entirely, immune 

 and so ought to be valuable for this purpose. 



This method was used with complete success by Schroeder^ in 

 Germany against the stem nematode (Tylenchus dipsaci) after all 

 other practicable methods had failed. lie planted infected fields for 

 a series of years with crops not susceptible to the nematode. After 

 this period the fields gave again their normal 3'ields of susceptible 

 plants. 



RECOMMENDATIONS FOR FREEING A FIELD FROM ROOT-KNOT. 



In view of the results of the experiments described, the writer 

 would make the following recommendations for freeing a field from . 

 root-knot. If the situation is one where the winters are cold and 

 cool weather sets in in October, it ^vi)l not be necessary to give 

 attention to the subject during the fall and winter or in the spring 

 before the ground begins to warm up. Under such conditions it 

 would probably suffice to plow the land in the autumn, so as to have 

 it in good condition for as early planting as possible in the spring. 

 In the spring the field should be kept free from vegetation by cultiva- 

 tion or harrowing until the ground is warm enough to plant cowpeas. 

 The field should then be planted tliickly with Iron cowpeas, this 



1 Rolfs, 1898. 2 Neal, 1S89. » Schroeder, 1902. 



217 



