the stem. The technique appears useful only for experimental 

 purposes. 



Once plants germinate, stakes are normally used. Because of 

 the extreme vigor of the plants, long stakes (2.5 to 3 meters) are 

 recommended. The vines then quickly establish a dense cover along 

 the length of the stake. Staking systems developed for other yams 

 should be equally suitable for D. trifida, but the amount of vines 

 that need support is great, and weak stakes will be pulled to the 

 ground. 



Satisfactory field growth and exceptional yields of up to 55 

 tons per hectare have been obtained in Guadeloupe without stak- 

 ing. The comparative costs and yields of stakeless culture need 

 further evaluation for this species. 



Pest Control 



In many areas of its distribution, D- trifida is remarkably free 

 from pests and diseases. This condition probably would not hold 

 true when the species is grown on a sufficient scale to permit 

 insects and diseases to multiply. However, yams in general are 

 relatively pest free. 



Research in various parts of the world has shown that chemi- 

 cal pesticides effectively control certain pests in yam plantations. 

 Most countries regulate the use of pesticides and establish the 

 amount of pesticide residues permitted on raw agricultural com- 

 modities, including imported commodities. (In the United States, 

 the Environmental Protection Agency is responsible for this activ- 

 ity.) In the following discussion, mention of a particular pesticide 

 should not be construed to mean that its use on yams is legal in 

 the United States or in any other country, or that residue toler- 

 ances have been established. The reader is cautioned to determine 

 the status of every pesticide in the country where it is to be applied 

 and to consult the appropriate authorities of an importing country 

 concerning permissible residues. 



Weeds 



Weed control can be a problem from the beginning. Newly 

 prepared clearings in the forest are not much troubled by weeds, 

 and the minimum weed control necessary is achieved by pulling 

 weeds. In Guadeloupe, atrazine^ applied as a preemergence spray 

 at the rate of 2.5 to 3 kilograms per hectare has successfully con- 

 trolled weeds until tubers germinate. After germination, one or 

 two hand weedings are necessary, or paraquat can be applied care- 



2-Chloro-4- (ethylamino) -6- (isopropylamino) -s-triazine. 

 5 l,l'-Dimethyl-4,4'-bipyridinium ion. 



17 



