48 BULLETIN 427, tJ. S. DEPARTMENT OF AGRICULTURE. 



seems that the destruction of the tuber-moth eggs and larvae is more 

 accidental than natural. 



Several species of spiders which are found in the fields spin webs in 

 which dead tuber moths have been noticed, and in a few cases the 

 spiders have been observed kilhng moths caught in the webs. 



ARTIFICIAL CONTROL. 



INDIRECT METHODS, GOOD FARMING. 



A study of the literature of the tuber moth shows that many writers, 

 beginning with Capt. Berthon (1), have recommended good farming 

 and careful harvesting and storing of tubers as the best remedies 

 against the tuber moth. The powers of reproduction of this insect 

 have given weight to these arguments, and a study of cultural methods 

 in relation to tuber-moth infestation has proved the correctness of 

 their recommendations. 



Through the kindness of Mr. S. S. Rogers, of the University of Cali- 

 fornia, the writer was enabled to compare the results of different cul- 

 tural methods. The test field, situated near Van Nuys, Cal., had 

 every conceivable variation in culture. Planting depth varied from 

 2 to 16 inches. Each plat contained both flat and ridged culture and 

 was harvested in three parts, so that each variation in culture had 

 early, medium, and late harvesting. 



The results may be briefly summarized as follows : 



Taking the entire field as an average, the percentage of infestation 

 in the plats having ridged culture was 8 per cent less than in those 

 having fiat culture. 



In the same way the plats harvested early had 4 per cent less infes- 

 tation than those harvested at the medium period and 9 per cent less 

 than those harvested late. 



In the experiments with depth of planting results were even more 

 striking. In the plats planted 2 inches deep (many tubers were ex- 

 posed) the vines were dead, and the percentage of infestation of the 

 tubers varied from 98 to 100. From this the percentage of infestation 

 became steadily less, as the depth of planting was increased, until at 

 a depth of 6 inches a minimum was reached, several plats giving 

 entirely clean potatoes and the average of infestation being low. In 

 the plats where deeper planting was used, the potatoes seemed to grow 

 as near the surface as where 5 to 6 inches planting depth was used, 

 and consequently there was no difference in freedom from the moth. 



Results from the experiments as to time of planting varied so 

 greatly that it was evident several other factors have more to do 

 with determining infestation than the time of planting. The same 

 might be said of the variety test, except that the tubers of varieties 

 where the vine stayed green the longest suffered least from the 

 moth. 



