Storage rot of seed yam resulting from speargrass injuries

Postharvest rot due to injury is a major contributing factor to the declining quality of stored seed yams (Dioscorea spp.). Among the several known injuries, the piercing effect of speargrass rhizomes has become a serious constraint for yam production in Ghana. The objective of this study was to assess injuries on seed yams resulting from piercing of speargrass rhizomes and their effects on postharvest rots in Ghana. Eighty farmer fields from Mem, Watro, Asanteboa and Abour in the Atebubu-Amantin Municipal in the Bono East Region of Ghana were screened for speargrass incidence and injury on harvested tubers, for laboratory analysis of pathogens in 2016 and 2017. The tubers were sorted into four categories of seed yam based on weight. Thirty seed yams each of two selected white yam cultivars (Dente and Kpamyo) with visible speargrass rhizome-pierced-tubers (VSRPT) and non-speargrass rhizome pierced healthy tubers (NSRPHT) were randomly selected and stored in a ban for weekly assessment of rot. The rotten tissues from the localised area of VPSRT were subjected to pathological investigations in the laboratory. The incidence of injury seemingly increased with increasing tuber weight. It was 0% for < 100 g samples and averagely 14% for > 1 kg samples, irrespective of cultivars and locations. Incidence of rot from NSRPHT sample was observed 5 weeks after storage (WAS) for both cultivars; and 2 WAS from the VSRPT sample and 40% higher than NSRPHT at 8 WAS. Eight and six known rot pathogens were isolated from the rotten tissues of VSRPT of Dente and Kpamyo, respectively. Injury from the piercing of speargrass rhizome significantly contributed to hastening of tuber rots; while tuber injury increased with increasing speargrass density. Appropriate management of speargrass is essential for commercial seed yam growers to reduce tuber damage which affects yam quality, storage and marketing. Key words: Dioscorea, postharvest, rot pathogen, speargrass rhizome

Weed Control and Tolerance of Sulfonylurea Herbicides in Caladium

Control of broadleaf weeds in caladium is difficult due in part to a lack of selective POST herbicides. Cultivation is not an option due to the dense canopy and potential for tuber injury. As a result, growers currently rely on preemergence (PRE) herbicide and hand-weeding. The objective of this research was to evaluate the control of four common broadleaf weeds of field grown caladium with POST applications of halosulfuron, thifensulfuron-methyl, and trifloxysulfuron, and determine the tolerance of caladium cultivars ‘Florida Fantasy’ and ‘Florida cardinal’ to POST applications of halosulfuron. At 4 weeks after treatment (WAT), thifensufluron-methyl at 28 g ai ha−1 and trifloxysulfuron at 84 g ai ha−1 provided approximately 90 and 70% common purslane control, respectively, while halosulfuron at 210 g ai ha−1 provided 55% suppression. Trifloxysulfuron controlled ≥90% spotted spurge at 42 g ha−1, whereas the highest rate of halosulfuron and thifensulfuron-methyl only achieved 60% suppression. In field experiments, the evaluated sulfonylurea (SU) herbicides were less efficacious on hairy indigo and sharppod morningglory as control never exceeded 65 and 50%, respectively. In greenhouse experiments, the evaluated halosulfuron rates ranging from 26 to 420 g ha−1 did not significantly reduce caladium tuber weight from the nontreated control. Averaged over halosulfuron rates, ‘Florida Fantasy’ damage was 5 and 6% at 2 and 4 WAT, respectively, while ‘Florida Cardinal’ damage was 11%. We conclude that none of the herbicide treatments effectively controlled all species evaluated. Sequential treatments, higher rates, or tank-mixtures may be necessary to adequately control these species. We also conclude that caladium cultivars ‘Florida Fantasy’ and ‘Florida Cardinal’ have acceptable tolerance to POST applications of halosulfuron. Further research is needed to evaluate caladium tolerance to other SU herbicides.