Yam Protection: I: Seed-Piece Treatment with Fungicide

Abstract

Preplant fungicide baths were tested on yam (Dioscorea rotundata Poir cv. Habanero) seed pieces (114-g sections) from sound tubers to determine their effect on emergence and yield of yams. Field plots were free of damaging populations of parasitic nematodes and had not been previously planted with yams. Yam seed pieces treated with captan or captan plus thiabendazole or captan plus benomyl increased field emergence (95, 96 and 91%, respectively) over that of nontreated controls (52%). Early emergence (5 weeks after planting) was greater for captan plus thiabendazole (24%) than for captan plus benomyl (1%), captan alone (2%), or the nontreated control (1%). Final stand counts (9 weeks after planting) were not statistically different among the fungicide treatments (91-96%). These counts were highly correlated with total tuber yield (r = 0.84**), total number of harvested tubers (r = 0.77**), and mean tuber weight (r = 0.74**). Plants from nontreated seed pieces produced a higher number of tubers per plant (1.64) compared with those from fungicide treated seed-pieces (1.16-1.20). Yield losses in nontreated seed pieces (48%) were related to losses in mean tuber weight (37%) and in total number of tubers (20%) per area when compared to the treated seed pieces. Greatest per plant and total yield and greatest tuber weight were found for the captan plus thiabendazole treatment, compared with captan alone or captan plus benomyl. Early and greater emergence of yam seed pieces appear to be important determinants of yield and tuber size in Habanero yams. In this experiment, even with good seed pieces and in a well-prepared seedbed, yam emergence and yield were diminished by one-half without fungicide treatment.