be stored in piles or in damp situations, as these conditions in- 

 crease rotting. Rotting is also associated with insect damage and 

 nematode infestation, and control of these pests greatly reduces 

 loss in storage. 



Various organisms are associated with rot, and these vary 

 from region to region. The principal organisms in West Africa 

 are Botryodeplodia theobromea, Rhizoctonia solani, and Fusarium 

 oxysporum. Penicillium oxalicum, Aspergillus niger, and various 

 other organisms have also been found. Soft rot of seed pieces can 

 be controlled by dipping them in benomyP or thiabendazole^ at 

 500 to 1,000 parts per million in water {20). The tuber pieces 

 should be planted directly after treatment. Although the same 

 fungicides help control rot in storage, they should not he used if 

 tubers are to be eaten later. 



The treatment of tubers, especially their young tips, with 

 indoleacetic acid reportedly reduces storage rot, even when yams 

 are piled, but these results could not be repeated in trials in 

 Nigeria. The common treatments with wood ashes or lime, are 

 simple, useful methods on the farm. 



Staking 



Some kind of support (fig. 10) is usually required for good 

 production of yams. D. rotundata and D. cayenensis are sometimes 

 grown without support, but the sacrifice in yield is so great that 

 only dire shortages of labor or staking material should prevent 

 staking. 



The staking system should be built of local materials. Crude 

 sticks or branches, slim bamboos, or bamboo side branches are 

 often used. Sometimes dead materials from previous crops such 

 as corn, sorghum, or tobacco are used, but these usually do not 

 last long enough to give support through the growing season. 

 The use of living plants is not recommended because they compete 

 with the yams and severely reduce yields. Nevertheless, because 

 the staking of yams is so costly, further attempts to develop a 

 living-plant system, especially with legumes such as Cajanus and 

 Sesbania, should be made. 



One of the best staking systems yet designed is described by 

 Wholey and Haynes (30). Twelve-foot teak poles are strung with 

 12-gage galvanized wire 6 to 8 feet off the ground and tied to 

 stakes driven into the ground. Two rows of yams are planted, one 

 on each side. When the vines have developed sufficiently, strings 

 are tied to them and passed over the wire. Access to the planting 

 is provided by furrows equidistant between poles. In a variation of 



^ Methyl 1- (butylcarbamoyl) -2-benzimidazolecarbamate. 

 ^ 2- (4-Thiazolyl) benzimidazole. 



27 



