22 AGRICULTURE HANDBOOK 495, U.S. DEPT. OF AGRICULTURE 



PN-4445 



Figure 9. — D. alata growing without stakes. 



greater yam beetle, passes through 

 its mating and reproduction cycle 

 in swamp ground but migrates to 

 yam plantings for feeding. In 

 Puerto Rico white grubs, Lach- 

 nosterma spp. and Diaprepes ahre- 

 viatus, often cause extensive dam- 

 age to the tubers. These beetles 

 have been controlled by the appli- 

 cation of insecticides to the soil, a 

 risky practice. In most parts of the 

 world yams are not treated in any 

 way to protect them from insect 

 pests. 



A serious plague limiting yams 

 in some areas is the nematode. Al- 

 though these small organisms have 

 been chiefly associated with Afri- 

 can species, they can also be very 

 detrimental to D. alata. The spe- 

 cies attacking yams are Scutel- 



lonema hmdys (Steiner and Le 

 Hew) Andrassy, Meloidogyne 

 spp., and Pratylenchus spp. Dam- 

 age occurs chiefly to the tubers, 

 in the form of superficial lesions 

 that permit the entrance of fungi. 

 Where yams are grown in sandy 

 soils, nematodes constitute a ser- 

 ious problem and control is diffi- 

 cult. Practical control includes the 

 use of clean seed materials and 

 planting in heavy soils, where 

 nematodes might not occur. In 

 some cases hot-water treatment 

 kills the nematodes in the tissue. 

 Extended cool treatment in a re- 

 frigerator is also useful. Nema- 

 todes are often present in harvest- 

 ed yams and may continue to live 

 and multiply in stored tubers (29). 

 They are suspected to be associated 



