Table 4. — Effects of two temperatures on storage rot, mealy hug 

 infestation, sprouting of tubers, and dry-weight loss of cush- 

 cush yams 



Type of deterioration 







18° C 







26° C 





1 mo 



2 mo 



3 mo 



1 mo 



2 mo 



3 mo 



Storage rot 



mm . • . 





23 



34 





12 



16 



Mealy bug infestation 





7 



22 



22 



11 



80 



86 



Sprouting of tubers • • 





38 



90 



100 



92 



100 



100 



Dry-weight loss 



..%... 





16 



24 





21 



38 



some pest. From 10 to 30 percent of the tubers are usually affected 

 by rot. 



Mealy bugs (P. citri, P. gossypii) , which migrate from stems 

 to stolons and tubers when maturation occurs, form mixed colonies 

 on stored cushcush. With as a few as 1 or 2 percent contaminated 

 tubers at harvest, mealy bugs can multiply during storage and 

 infest 80 percent of tubers within 2 months. Infection during 

 storage is often related to the appearance of sprouts, which they 

 colonize and sometimes destroy. 



The mealy bug endoparasite Leptomastix dactylopii (En- 

 cyrtide) attacks P. citri and P. gossypii but not enough to give 

 natural biological control. Chemical control is obtained by a 10- 

 minute dip in 0.5 gram malathion^ per liter of water, but such 

 pesticide must be limited to seed tubers. Storage at cool tempera- 

 tures in the dark partially controls mealy bugs (table 4). Cool 

 storage also reduces sprouting and loss of dry weight, but can in- 

 crease rotting. P. Ricci (personal communication, 1976) has found 

 that respiratory intensity increases sharply after infection by P. 

 oxalicum. Curing, as done with other yams, is not effective for 

 control of P. oxalicum rot. Complete protection can be achieved by 

 a fungicidal dip of 1 milliliter thiabendazole^ suspended in 4 liters 

 of water in the first days after harvest. Benomyl has been 

 successfully used at 0-1 gram per liter of water {32). 



A final source of storage decay in cushcush tubers is nema- 

 todes. High populations of P. coffeae have been found in Jamaica, 

 associated with dry rot of the flesh, which is reduced to a dark- 

 brown powder. The skin, at first firm, becomes brittle and flakes 

 off. At this stage saprophytic nematodes (Aphelenchus sp., Aphe- 

 lenchoides spp.) can be also found (19). It appears that incidences 

 of nematode infestation can be limited in the field, but nematodes 

 may cause heavier potential loss in storage. 



In summary, storage in a dark, cool room (16° to 18° C) of 



6 Diethyl mercaptosuccinate ^S-ester with 0,0-dimethyl phosphorodithioate. 

 ^ 2-(4-Thiazolyl)benzimidazole. 



21 



