Abstract
Two experiments were conducted, one each at Utuado and Corozal, to evaluate the effect of a soil spray and a seed treatment with the systemic nematicide-insecticide Oxamyl L and soil treatments of Phenamiphos 15G for the control of the nematode Pratylenchus coffeae (Zimmerman) Filip. Sehuur-Stekh. and the white-grub, Diaprepes abbreviates (L.), in yam (Dioscorea rotundata Poir). The soil was sprayed at the base of the plant with a 20 ml automatic applicator (Spot Gun). At Utuado, two doses of oxamyl, 0.3 ml (7,410 µg a.i./ml) and 0.6 ml (1 5,297 ug a.i./ml) per plant applied every two months were evaluated alone and in combination with a seed immersion in 2,400 p/m a.i. of oxamyl/15 min. Also seed immersion was evaluated when combined with foliar sprays of Oxamyil L (4.68 l/ha every 15 and 60 days). At Corozal soil spray of Oxamyil L [0.6 and 0.9 ml (23,700 µg
a.i./ml)/plant], 0.3 and 0.6 ml/plant plus seed treatment (2400 p/m a.i./15 min), Oxamyil L sprayed at 4.68 l/ha/15 days and soil treatments of Phenamiphos (0.64, 0.93 and 1.27 g/plant) were evaluated. Harvested tubers were classified in quality categories based on the cortical dry-rot damage caused by P. coffeae: high (0-25%), medium (26-50%) and poor (51-100%); and based on perforations made by the larvae of D. abbreviates: tunneled (tubers with one or more perforations) and marketable (high and medium quality tubers without tunnels). Significant yield increases (P = 0.01) of high quality yams over the control were obtained at both locations with all Oxamyil L treatments. Highest yields were obtained at Utuado with 0.3 ml/plant combined with seed immersion and with 0.6 ml/plant without seed treatment. An increase from 0.6 to 0.9 ml of Oxamyil L did not increase yields significantly at Corozal. At Utuado there was no significant reduction in tunneled yams attributable to foliar spray or soil treatments. Infestation of D. abbreviates at Corozal was very low.