Determination of Pesticide Residues in Organic and Conventional Exotic Vegetables

Pesticides are used to protect crops from diseases and pests. Their application in agriculture has been in existence since ancient times to date. They have also been used in growing vegetables especially exotic vegetables that are more prone to pests and diseases. There have been concerns over indiscriminate use of pesticides by farmers to grow vegetables especially for local markets since there are no guidelines on Maximum residue levels. This study was done to determine the concentration of cypermethrin and lambda-cyhalothrin pesticide residues in Collard (Brassica oleracea var. acephala) Tomatoes (Solanum lycopersicum) and swiss chard (Beta vulgaris subsp. cicla). The samples included both organic and conventional vegetables that use chemical pesticides. Experimental study design was used which involved laboratory analysis of the samples. Sample extraction was done using AOAC official method 2007.01 known as Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method. The method involves use of Acetonitrile, sodium chloride and anhydrous magnesium sulphate for extraction. Clean-up was done using dispersive-solid phase extraction method using Primary-Secondary Amine and anhydrous magnesium sulphate. Residues analysis was done using Reverse-phase High Performance Liquid chromatography. Peak areas of the curves were calculated using Motic Images plus 2.0 and data analysis was done using SPSS 22. Recovery rates of pesticide ranged from 87.78% to 97.93% for cypermethrin and 90.65% to 95.72% for lambda-cyhalothrin. The results indicated that organic vegetable samples had pesticide residues below detectable levels while conventional vegetable samples had levels ranging from 2.495mg/kg to 0.238mg/kg for cypermethrin and 0.352mg/kg to 0.119mg/kg for lambda-cyhalothrin. The residues of both pesticides were above the recommended, this is likely to cause negative health effects such as uncoordination, whole-body tremors and seizures. This indicates that conventional vegetable consumers are exposed to pesticide residues. Farmers should strictly adhere to good agricultural practice to reduce pesticide residues

Flowering margins support natural enemies between cropping seasons

Here we investigated how agricultural landscapes support natural pest regulating insects between cropping seasons; an important challenge in Pest Management by Small-Holder Farmers so aligns with this special issue. Smallholders in East Africa clear margins to provide fodder for cattle or livestock or simply to reduce the ingression of weeds into crop fields. We show that there was a significant seasonal variation in plant species richness and diversity around crops and the abundance of margin plants was strongly linked to abundance of natural enemies in the off season. The time since harvesting was also a significant factor influencing the overall abundance of natural enemies. Our paper reinforces our understanding of the importance flowering plants in agricultural systems as a refuge for natural enemies and other beneficial insects but uniquely emphasising the time between cropping seasons. Improving agricultural landscapes between crops to better support invertebrates will lead to more effective natural pest regulation early in the following crop with positive outcomes for the farmers and their families

Flowering margins support natural enemies between cropping seasons

IntroductionPopulations of natural enemies of insect pests are declining owing to agricultural intensification and indiscriminate use of pesticides, and this may be exacerbated in agricultural systems that clear all margin plants after the cropping season for other uses such as fodder. Retaining a diversity of non-crop flowering vegetation outside the cropping season may support more resilient and effective natural pest regulation.MethodsWe tested the potential for non-crop vegetation to support natural enemies in fields across two locations after harvesting the primary crops of lablab and maize.ResultsA total of 54 plant species were recorded across the sites in Kenya with 59% of them being annuals and 41% perennials. There was a significant seasonal variation in plant species richness (ANOVA: F1, 16 = 33. 45; P< 0.0001) and diversity (ANOVA: F1, 16 = 7.20; P = 0.0511). While time since harvesting was a significant factor influencing the overall abundance of natural enemies (ANOVA: F2, 1,133 = 8.11; P< 0.0001), they were generally higher in abundance in locations with margin plants or where a diversity of margin plants was observed.DiscussionThese findings demonstrate that flowering plants in agricultural systems offer refuge and alternative food for natural enemies and potentially other beneficial insects between cropping seasons. The conservation of natural enemies between crops may lead to more effective natural pest regulation early in the following crop, thus reducing reliance on insecticides application

Field margins and cropping system influence diversity and abundance of aphid natural enemies in Lablab purpureus

Field margin plants around crops are postulated to increase natural enemy abundance to enhance pest management. A trial was conducted to determine the contribution of field margin vegetation and cropping systems to natural enemies of bean aphids (Aphis fabae) on Lablab purpureus, an orphan crop legume. Natural enemy populations were surveyed in plots with cross combination of lablab monocrop or maize-lablab intercrop and with or without planted field margins comprising four plant species (Chenopodium album, Bidens pilosa, Galinsoga parviflora and Tagetes minuta), arranged in randomized complete block design with four replicates. A cage experiment was also conducted to understand the extent to which these field margin plants supported the parasitoid wasp, Aphidius colemani, to parasitize bean aphids. A total of 2029 insects from 10 families were collected using sticky cards and pan traps. In comparison to plots with no field margin plants, the presence of plant-rich field margins increased abundance of natural enemies by (9.5 %) and supported higher populations of Braconidae (parasitoids) and damsel bugs (predators). The maize-lablab intercrop had 15.5% lower abundance of natural enemies than the lablab monocrop. Higher grain yield was recorded in plots with a field margin vegetation (300 kg ha-1) compared to plots without field margin vegetation (210 kg ha-1). The presence of a companion plant did not significantly affect the performance of parasitoids, in the cage experiment, indicating that parasitoids were not limited by access to food. In supporting aphid parasitization, B. pilosa was associated with the highest number of mummies (8.28). The lowest number of mummies were observed in cages with T. minuta (3.44). These results demonstrate the potential of plant-rich field margins to augment natural enemy populations and enhance conservation biocontrol of aphids

Intercropping and diverse field margin vegetation suppress bean aphid (Homoptera: Aphididae) infestation in dolichos ( Lablab purpureus L.).

Dolichos (Lablab purpureus L.) is a drought tolerant legume used as food/feed and im- provement of soil fertility. The production of dolichos in Kenya, Nakuru County is however limited by insect pests like bean aphids, pod borers and whiteflies. Field stud- ies were conducted to determine the effect of cropping systems (dolichos monocrop and maize-dolichos intercrop) and field margin vegetation on bean aphids and their natural enemies. The experiment was conducted in Njoro (high field margin vegetation) and Ron- gai (low field margin vegetation) during May–December 2019 and March−November 2020 cropping seasons. Bean aphid percent incidence, severity of damage and abundance was assessed at seedling, early vegetative, late vegetative and flowering dolichos growth stages. The populations of natural enemies in the plots and field margin vegetation were monitored using pan traps and sweep nets. Species diversity and composition of the field margin ve-getation was determined using a quadrat. Results showed that location and cropping system had significant effects on bean aphid infestations. A high bean aphid incidence (38.13%) was observed in Njoro compared to Rongai (31.10%). Dolichos monocrop had significantly higher bean aphid infestation (51.63%) than the maize-dolichos intercrop system (24.62%). A highly diverse Shannon-weaver index was observed in Rongai (1.90) compared to Njoro (1.67). Dolichos monocrop had a more diverse Shannon-weaver index (1.8) than the maize- dolichos intercrop system (1.7). Rongai had the most abundant annual and perennial field margin vegetation species. The field margin species richness and diversity were higher in Rongai (81%) than in Njoro (54%). The findings of this study have demonstrated that a maize-dolichos intercrop in Rongai can reduce bean aphid damage in dolichos

Lablab (Lablab purpureus L.) genotypes and field margin vegetation influence bean aphids and their natural enemies

Dolichos bean (Lablab purpureus L.) is an important food and livestock feed legume that can also enhance soil fertility. However, its production is limited by insect pests, notably the black bean aphid (Aphis fabae). The present field study was conducted to determine the difference in contribution of dolichos genotypes and natural field margin vegetation (FMV) on the abundance and diversity of natural enemies and the damage, incidence and abundance of bean aphids. Eighteen lablab genotypes were planted in the presence or absence of FMV in a randomized complete block design 24 experiment replicated four times. Data on aphid abundance, incidence and severity of damage were collected at four growth stages of the crop. Dolichos genotypes significantly influenced aphid incidence thereby suggesting some level of tolerance to aphid colonization. Findings showed that dolichos genotypes were significant for natural enemies species richness with no statistical difference for abundance and natural enemies species diversity. However, the genotypes did not vary significantly in their influence on numbers of aphid natural enemies. FMV was associated with low bean aphid damage. Overall, the presence or absence of FMV did not influence the number of natural enemies caught on the crop. This concurs with recent work that shows similar numbers of natural enemies with field margin plants but may reflect the reduced number of pest insects. Cropping seasons influenced aphid abundance and damage severity, with the populations developing at early stages of lablab development and decreasing as the crop advanced. This pattern was similar both in presence or absence of FMV. The findings of this study highlight the important contribution of crop genotype together with the presence of field margin species in the regulation of aphids and their natural enemies in lablab

Field margins and botanical insecticides enhance Lablab purpureus yield by reducing aphid and supporting natural enemies

Botanical insecticides offer an environmentally benign insect pest management option for field crops with reduced impacts on natural enemies of pests and pollinators while botanically rich field margins can augment their abundance. Here we evaluated the non-target effects on natural enemies and pest control efficacy on bean aphids in Lablab of three neem and pyrethrum based botanical insecticides (Pyerin75EC®, Nimbecidine® and Pyeneem 20EC®) and determine the influence of florally rich field margin vegetation on the recovery of beneficial insects after treatment. The botanical insecticides were applied at early and late vegetative growth stages. Data was collected on aphids (abundance, damage severity and percent incidence) and natural enemy (abundance) both at pre-spraying and post-spraying alongside Lablab bean yield. The efficacy of botanical insecticides was similar to a synthetic pesticide control and reduced aphid abundance by 88% compared to the untreated control. However, the number of natural enemies was 34% higher in botanical insecticide treated plots than in plots treated with the synthetic insecticide indicating that plant-based treatments were less harmful to beneficial insects. The presence of field margin vegetation increased further the number of parasitic wasps and tachinid flies by 16% and 20%, respectively. This indicated that non-crop habitat can enhance recovery in beneficial insect populations and that botanical insecticides integrate effectively with conservation biological control strategies. Higher grain yields of 2.55-3.04 and 2.95-3.23 t/ha were recorded for both botanical insecticide and synthetic insecticide in the presence of florally enhanced field margins in consecutive cropping seasons. Overall, these data demonstrated that commercial botanical insecticides together with florally rich field margins offer an integrated, environmentally benign and sustainable alternative to synthetic insecticides for insect pest management and increased productivity of the orphan crop legume, Lablab