MIXED CROPS. 69 



but in a proper compost heap. The useless cotton bolls not worth pick- 

 ing- breed cotton pests and do much harm; they should be removed 

 periodically and carefully burnt with all their inhabitants. He who 

 leaves fallen mangoes to rot where they fall should not be surprised if 

 his sound mangoes are attacked by pests bred in the fallen ones. 



Rotation of crops is a practice of some value and is more valuable 

 the larger the area rotated. Keeping two acres side by side in sorghum 

 and cotton alternately does not help matters so far as insects are con- 

 cerned ; but the rotation of large blocks of land in alternate crops does 

 much to check pests. In rare cases it is possible to check a pest by not 

 growing its food-plant for a year or longer, substituting other crops. 



The practice of growing mixed crops has a profound influence upon 

 insect life and is generally most beneficial. Growing crops in separate 

 blocks which might be mixed and grown in alternate rows is a direct 

 incentive to insect attack, and the mixed cultivation of the Indian culti- 

 vator might well be followed in other countries where pests are rife. 

 Mixed crops approximate to natural conditions and discourage the 

 increase of insect pests. Cotton grown with tur, urd or maize suffers 

 less from insect pests which do not so easily find the cotton ; the moth 

 has to search for her food-plants, and in so doing runs risks of enemies ; 

 the caterpillars cannot simply crawl from plant to plant, but must move 

 over the ground with the risk of being snapped up by ground beetles, 

 frogs or birds. The mixed crop is a great safeguard, though the cultivator 

 does not know the reason but benefits by the accumulated experience of 

 distant ages. Opposed to the mixed crop is the small plot of any 

 single crop. A small area of a single crop in a large area of other crops 

 is an inducement to insects to cluster in that small plot, and destroy it. 

 Insects which are harmless when scattered over one thousand acres are 

 extremely destructive in a small plot, and probably devour it all. Nothing 

 is more fatal than to grow a small area of a plant ; it is not the small 

 plot but the relative area which matters ; if a crop is grown in its due pro- 

 portion, say one thousand acres in five thousand, it may be broken up 

 into small plots, but the insects are scattered over the district ; but if 

 there is only one plot of say ten acres in that five thousand acres, then 

 that plot is liable to suffer. Many promising experimental cultivations 

 of crops suffer because insects gather in that one little plot. If the 

 experiment had been on a larger scale or if the pests had been checked, 

 the experiment would have had a better chance of giving true results. If 

 one grows plants under such conditions, one must expect abnormal results 

 and take measures accordingly. 



Much encouragement is given to pests by the promiscuous growth 

 of plants that harbour pests at seasons when the crops are not available* 



