308 TROPICAL AGRICULTURE 



have been grown in the Tropics. In general, Turkestan and 

 Arabian alfalfa have given better results in point of yield 

 and in quick growth after cutting than the conunon alfalfa. 

 Alfalfa may be depended upon in tropical climates to yield 

 a crop each month the year round. It is therefore not so 

 necessary to cure the crop for hay as in cold climates, since 

 it is possible to secure a continuous supply of green feed 

 from a plantation of alfalfa. Under favorable conditions 13 

 crops have been obtained in 12 months. 



It is particularly desirable in planting alfalfa in the Trop- 

 ics to avoid infestation with dodder as far as possible. Dod- 

 der, like the alfalfa, of course, grows the year round and 

 spreads with sufficient rapidity to be a very setious pest if 

 once introduced into a field of alfalfa. While it is customary 

 to harvest 10 to 13 crops of alfalfa per year in tropical cli- 

 mates, the total annual acre yield is not higher than is 

 obtained in favorable localities in Arizona, New Mexico, and 

 California. 



If it were not for the unusually serious attacks of plant 

 lice, to which cowpeas seem to be particularly susceptible, this 

 crop would be perhaps the most valuable leguminous crop 

 for forage and green manuring in most tropical countries. In 

 some localities, however, the planting of cowpeas is a hazard 

 on account of the frightful scourge of plant lice. A fine 

 crop of cowpeas may be entirely destroyed in the course of 

 10 days. In some instances, the whole surface of the plants, 

 stems, and leaves are completely covered with plant lice. Lady 

 birds and parasitic insects multiply with great rapidity, but 

 these natural enemies of the plant lice seldom succeed in 

 destroying them before the cowpea crop is ruined. 



In general, it has been found that the drier and warmer 

 regions and seasons are best adapted to this crop and it should 

 preferably be grown without irrigation. The largest yields 

 of seed and forage are obtained when the crop is drilled in 

 rows and well cultivated between the rows. 



