Dissipation, accumulation, distribution and risk assessment of fungicides in greenhouse and open-field cowpeas

Pesticide residues in cowpeas have raised worldwide concern. However, only a few studies have focused on pesticide accumulation and distribution in greenhouse and open-field cowpeas. Field trial results suggest that difenoconazole, dimethomorph, thifluzamide and pyraclostrobin dissipated faster in open fields (mean half-lives, 1.72-1.99 days) than in greenhouses (2.09-3.55 days); moreover, fungicide residues in greenhouse cowpeas were 0.84-8.19 times higher than those in the open-field cowpeas. All fungicides accumulated in the greenhouse and open-field cowpeas after repeated spraying. Fungicide residues in old cowpeas were higher than those in tender cowpeas, and residues in the upper halves of cowpea pods were higher than those in the lower halves. In addition, cowpeas distributed in the lower halves of the plants had higher fungicide residues. Our findings suggest that greenhouse cultivation contributed to the pesticide residues in cowpeas after repeated spraying, although the levels of dietary health risks remained acceptable under both cultivation scenarios.

Modification of the functional properties of hard-to-cook cowpea seed flours and cooked prepared pastes by γ-irradiation

Cowpeas are an inexpensive source of quality protein but their utilisation is limited by long seed cooking time. This is exacerbated by development of the hard-to-cook (HTC) defect, which also adversely affects starch and protein functionality. Gamma-irradiation can eliminate cowpea seed insect infestation and affects seed functional properties, including reducing cooking time. Hence, the potential of γ-irradiation to modify the starch- and protein-related functionalities of HTC cowpeas was investigated. Gamma-irradiation at approximately 11 kGy was applied to the seeds of two cowpea varieties, differing in HTC susceptibility, where HTC had been induced by high-temperature, high-humidity (HTHH) storage. HTHH storage increased flour pasting peak viscosity by up to 40% in the less susceptible variety and by more than 100% in the more susceptible variety. Gamma-irradiation at least completely reversed this effect, due to starch depolymerisation and debranching. Gamma-irradiation also positively impacted on some protein-related properties adversely affected by HTC; partially reversing the reduction in flour and cooked paste nitrogen solubility index of the HTC-susceptible cowpea, as a result of protein depolymerisation. The multiple benefits of γ-irradiation: disinfection, cooking time reduction and reversing some adverse effects of HTC on functional properties could make it a viable process for improving HTC cowpea quality.

Tamboti wood ash and burnt goat dropping ash, safe alternatives to control cowpea weevils, Callosobruchus maculatus (Fabr.) (Coleoptera: Bruchidae) during storage for subsistence farming

This study determined the effect of tamboti wood ash and burnt goat dropping ash along with a chemical insecticide (avi-klorpirifos) on the reproduction, egg hatchability, damage, and mortality of cowpea weevil (Callosobruchus maculatus Fabr.). The germination potential of treated cowpea seeds was also determined using a susceptible variety-Blackeye. Two hundred grams of clean cowpea seeds were mixed with 25 g of tamboti wood ash and goat dropping ash. These seeds were then infested with 5 pairs of newly emerged adults of C. maculatus under controlled laboratory conditions. The experiment revealed that both tamboti wood ash and goat dropping ash had negative effects on the efficiency of C. maculatus and significantly reduced the extent of damage. In germination test, these ashes showed a significant improvement in germinability of treated cowpea seeds. However, in all instances, tamboti wood ash proved to be much more effective than goat dropping ash. The study observed that these natural products have the potential to protect cowpea seeds from the damage caused by C. maculatus during storage and can, therefore, be used as an alternative pest management method against cowpea weevils.