Influences of fertilizing regime and shading on Mobydick stem yield, number of bolls and boll colouration

Asclepias fruticosa (Mobydick), a native plant that was recently (2004) domesticated is commercially produced as a cut-flower by Kenyan smallholder farmers for its green inflated bristly seed pods (‘bolls’). Over the last few years, there has been an increase in boll discolouration resulting to rejection of mobydick stems by exporters. The brownish/purplish colouration on the bolls is suggestive of some nutrient deficiency or toxicity. The ‘boll discolouration’ appears to be most severe on the side directly facing the sun, suggesting that shading may contribute to boll discolouration. A trial was conducted to test the effect of different fertilizing regimes (different combination of organic manure, DAP, 17-17-17, CAN and foliar feed fertilizers) and shading (outdoor and 50% shading) on percentage of boll bearing stems, total number of bolls and number of green + slightly discoloured bolls (g+sd) per plant. Percentage of boll-bearing stems in outdoor grown mobydick was four times that under shade. The crop fertilized with organic manure (OM) plus DAP at planting had the highest percentage of boll-bearing stems. Outdoor mobydick had more than 10 times the number of bolls in mobydick under shade. The fertilizing regime of OM + DAP at planting and OM + DAP + monthly top-dressing with CAN had more number of total bolls compared to the other regimes. Mobydick grown out-door had higher percentage of g+sd bolls (66.1%) than that grown under shade house (37.7%). Overall, percentage of g+sd bolls was higher in treatments where DAP was applied at planting, with or without monthly top-dressing with CAN and lowest in fertilizing regimes where no DAP was applied at planting and where 17-17-17 was used for top-dressing. It is recommended that mobydick should be grown outdoor and fertilized with organic manure and DAP at planting with or without top-dressing with CAN fertilizer.