Pest management is one of farmers’ foremost concerns with farmers reporting yield loss by termites, rodents, mealybug, nematodes, anthracnose, yam beetle, centipede, dry rot, die-back. A survey of yam farmers and market vendors across the ‘yam belt’ produced the most prevalent predator: dry rot disease-causing, parasitic nematodeScutellonema bradys, though Meloidogyne, Scutellonema, Pratylenchus were also detected. Further, infection was reported up to 47% by farmers and 18% by vendors.(Coyne)
//scutelonema bradys PHOTOChemical agents for biological control can have lasting and detrimental effects on the environment and is an important consideration in sustainable agricultural practices. In fact, some countries like Guadelopue prohibit the use of chemical pesticides. Safety concerns are also relevant; in particular, Yam Minisett Technique (YMT) officially introduced the use of pesticide dust (i.e. Aldrin/Lindane) for yam propagation, albeit rather poorly with many farmers unknowingly handling the toxins directly. More recently, AYMT has introduced a pesticide ‘dip’ of the insecticide, chlorporifos (branded Act Force Gold) and fungicide, mancozeb (branded Z force), eliminating direct contact with the pesticides but introducing the need for waste disposal for excess pesticide, which is most effectively buried to the detriment of soils’ life cycle. Alternatively, without the fallback of using pesticides, Guadeloupe has catalogued mulches, though expensive, producing 40% higher yields and requiring 75% less weeding than natural soils and compost-fertilizer mix with 20% increase in yields (Tournebize). Economics are determinant in agricultural practices; especially in some countries where organic labels can carry premium prices. In developing countries, unavailability of pesticides is also a factor to consider. Pragmatically, the solution for industrial agriculture must be both economical, effective, and sustainable. Relevantly, Osei et. al. () reported a reduction in parasitic nematode infestation (~68%) comparable to nematicide Fulan with a treatment of Mucuna puriens ‘velvet bean’ seed powder. As a compromise, against ’mealy bug’ Rhizoecus amorphophalli Betrem, a minimal 10-15mL/L biopesticide with cassava and neem extracts (Jayaprakas). Coincidentally, essential oils of D. compostia and D. floribunda contain insecticidal sesquiterpenes http://www.ncbi.nlm.nih.gov/pubmed/24453926 . Scaled-up production, just as with D. deltoidea, perhaps in combination with metabolic engineering could produce these insecticides for industrial use.
With growth spanning across continents and climates, Dioscorea is reasonably adaptable including some species with drought tolerance. However, since only a select few of Dioscorea species are edible, it is critical that domesticated varieties be adaptable to different soils and that soils maintain sufficient nutrient availability. Pigeonpea rotations promote higher tuber yields (Ennin). Similarly, ridged seedbeds promote higher yields rather than mounding in addition to being more conducive to mechanized farming. Regional field trials with various compositions of animal manure, city refuse, and chemical fertilizer have also worked to optimize nutrient recycling (Ennin, Lawal).
Most yams require considerable space to grow (e.g. George et. al. suggested 60 x 60 cm for D. alata). Alternatively, farms can provide stakes for the yam plants to ‘trail’ vertically for more space, however this is (1) labor intensive, thereby costly and (2) is leading to significant deforestation. While horizontal stalking can minimize damage by cutting the stake requirements in half (ennin), there remain two superior alternatives: dwarfism and intercropping. Dwarfism is a recessive trait which enables yams to grow equally well in terms of both yield and quality under more confined conditions. D. rotundata Drd-1068 and Drd-1157 in particular have been bred to leverage their dwarfism for especially high yields (~25 tons/ha) (Sheela) though optimization continues to maintain similarly high organoleptic qualities. Without these species/varietals, a synergy of intercropping corn (Zea mays) can provide yams with corn stalks to grow on in addition to provide an additional crop for consumption or revenue. Further, this synergy reduced anthracnose between 52.7-62.3%. Potentially, this synergy might be explained by trailing (opposite of dwarfism) genotype’s higher demand for calcium, potassium, and mangenesium(Suja). Regardless, it can be further enhanced with 2 t/ha mulch, yielding 21% and 10.3% higher production levels respectively for yam and corn (maniyam).