Patrick A. Ndakidemi

Extracts from Field Margin Weeds Provide Economically Viable and Environmentally Benign Pest Control Compared to Synthetic Pesticides

Plants with pesticidal properties have been investigated for decades as alternatives to synthetics, but most progress has been shown in the laboratory. Consequently, research on pesticidal plants is failing to address gaps in our knowledge that constrain their uptake. Some of these gaps are their evaluation of their efficacy under field conditions, their economic viability and impact on beneficial organisms. Extracts made from four abundant weed species found in northern Tanzania, Tithonia diversifolia, Tephrosia vogelii, Vernonia amygdalina and Lippia javanica offered effective control of key pest species on common bean plants (Phaseolus vulgaris) that was comparable to the pyrethroid synthetic, Karate. The plant pesticide treatments had significantly lower effects on natural enemies (lady beetles and spiders). Plant pesticide treatments were more cost effective to use than the synthetic pesticide where the marginal rate of return for the synthetic was no different from the untreated control, around 4USD/ha, compared to a rate of return of around 5.50USD/ha for plant pesticide treatments. Chemical analysis confirmed the presence of known insecticidal compounds in water extracts of T. vogelii (the rotenoid deguelin) and T. diversifolia (the sesquiterpene lactone tagitinin A). Sesquiterpene lactones and the saponin vernonioside C were also identified in organic extracts of V. amygdalina but only the saponin was recorded in water extracts which are similar to those used in the field trial. Pesticidal plants were better able to facilitate ecosystem services whilst effectively managing pests. The labour costs of collecting and processing abundant plants near farm land were less than the cost of purchasing synthetic pesticides.

Effects of phosphorus and Bradyrhizobium japonicum on growth and chlorophyll content of cowpea (Vigna unguiculata (L) Walp).

The field and screen house experiment was conducted at Tanzania Coffee Research Institute and Seliani Agricultural Research Institute respectively in Tanzania, between March-July 2013, to assess the effects of Bradyrhizobium japonicum and phosphorus on growth and total leaf chlorophyll content of cowpea. The experiment was out down in splitplot design whereby the main plots comprised two inoculation treatments (with and without B. japonicum), while the sub-plots contained phosphorus (TSP) application at four different levels (0 kg/ha, 20 kg/ha, 40 kg/ha, 80 kg/ha). Both experiments were replicated four times. We measured plant growth parameters such as plant height; number of leaves per plant at different stages of plant growth, the stem girth was measured by vernier caliper at physiological maturity. The chlorophyll content was determined at 3, 5, and 7 weeks after planting (WAP). The chlorophyll was extracted by using dimethylsulphoxide (DMSO) and absorbance was determined at 645 and 663nm using UV/Visible spectrophotometer. B. japonicum inoculation significantly increased the plant height, number of leaves per plants, and stem girth above the control. The height was increased by 11.23, 10.43 and 8.99% (screen-house) and by 8.11, 24.05, 9.29% (field) in the measurements taken at 4, 6, and 8 WAP respectively. Number of leaves per plant counted at 6 and 8 WAP increased by 14 and 10.8% (screen-house) and 14 and 11.6% (field) respectively. B. japonicum also Original Research Article American Journal of Experimental Agriculture, 4(10): 1120-1136, 2014 1121 significantly increased leaf chlorophyll content of cowpea by 26% (3 WAP) in screen-house and 52, 37.9 and 13.3% (3, 5 and 7 WAP) respectively on the field. Phosphorus also significantly increased different plant growth parameters and leaf chlorophyll content relative to control. B. japonicum inoculation can be as beneficial as inorganic N fertilizers. Therefore, their combined use with phosphorus boosts plant growth and chlorophyll content of the legumes and eventually legume production is increased.

Contact and fumigant toxicity of five pesticidal plants against Callosobruchus maculatus (Coleoptera: Chrysomelidae) in stored cowpea (Vigna unguiculata)

Insecticidal activities of five pesticidal plant species, Tephrosia vogelii, Dysphania (Syn: Chenopodium) ambrosioides, Lippia javanica, Tithonia diversifolia and Vernonia amygdalina, which have been reported to control storage pests, were evaluated as leaf powders against Callosobruchus maculatus (Fabricius 1775) in stored cowpea. Their efficacy was compared with the commercial pesticide Actellic dust (pirimiphos-methyl) at the recommended concentration (50 g/90 kg), and with untreated cowpea seeds as a negative control. The plant powders were applied at concentrations of 0.01, 0.1, 1 and 3g/10g of cowpea seeds in 250 ml plastic containers (to measure contact toxicity), or 0.005, 0.05, 0.5 and 5 g tied in small muslin cloth bags and hung in 500 ml plastic bottles containing 10 g of cowpea seeds (to measure fumigant toxicity). Mortality of adults, oviposition deterrence, adult emergence, and percent seed damage were recorded. Complete protection of seeds and inhibition of adult emergence were achieved in Actellic dust-treated seeds; contact toxicity using leaf powders of T. vogelii at all concentrations, D. ambrosioides at concentrations of 0.1,1 and 3 g and L. javanica at concentrations of 1 and 3 g; and fumigant toxicity using D. ambrosioides at concentrations of 0.5 and 5 g and L. javanica at a concentration of 5 g. Head space analysis of D. ambrosioides and L. javanica identified ascaridole and camphor, respectively, as components that could be responsible for the bioactivity of these plant species. These plants may, therefore, serve as effective but less harmful biopesticide alternatives to Actellic. Conversely, V. amygdalina and T. diversifolia were not effective, indicating that they should not be promoted for controlling bruchids in cowpea.

Dry bean response to fertilization using Minjingu phosphate rock and composted Tughutu (Vernonia subligera O. Hoffn).

Aims: The objectives of the study were toevaluate the effects of organic materials from Tughutu (Vernonia subligera O. Hoffn) and locally available Minjingu phosphate rock or commercial Triple super phosphate fertilizer on the plant growth and amount of phosphorus (P) and calcium (Ca) content in bean shoots (Phaseolus vulgaris L.) and their residual effects in the soil after harvest. Study Design: The experiments were set up as a randomized complete block design Place and Duration of Study: Field experiments were conducted in famers’ fields in the Western Usambara Mountains in Tanzania. Methodology: Each farmer’s field was assigned as a replicate. The experimental treatments consisted of six plots as follows: control, Minjingu Phosphate Rock (MPR) or Triple Super Phosphate (TSP) each at 26 kg P ha, Tughutu at 2.5 t dry matter ha and Tughutu at 2.5 t dry matter ha combined with Minjingu Phosphate Rock or Triple Super Phosphate at 26 kg P ha. Results: The dry matter yield and amount of P and Ca in bean shoots significantly increased by supplying the organic and inorganic fertilizers above the control treatment. Addition of P fertilizers alone or in combination with Tughutu also modified the soil pH and significantly increased the concentration of P and Ca in the soil at harvest. Conclusion: Overall, combination of Minjingu phosphate rock or Triple super phosphate with Original Research Article Ndakidemi; AJEA, 6(1): 51-59, 2015; Article no.AJEA.2015.064 52 Tughutu enhanced the effectiveness of these fertilizers and resultedin better growth and greater P and Ca amount in the shoots as well as their concentration in the soil at harvest.

Pesticidal Plant Extracts Improve Yield and Reduce Insect Pests on Legume Crops Without Harming Beneficial Arthropods.

In the fight against arthropod crop pests using plant secondary metabolites, most research has focussed on the identification of bioactive molecules. Several hundred candidate plant species and compounds are now known to have pesticidal properties against a range of arthropod pest species. Despite this growing body of research, few natural products are commercialized for pest management whilst on-farm use of existing botanically-based pesticides remains a small, but growing, component of crop protection practice. Uptake of natural pesticides is at least partly constrained by limited data on the trade-offs of their use on farm. The research presented here assessed the potential trade-offs of using pesticidal plant extracts on legume crop yields and the regulating ecosystem services of natural pests enemies. The application of six established pesticidal plants (Bidens pilosa, Lantana camara, Lippia javanica, Tephrosia vogelii, Tithonia diversifolia, and Vernonia amygdalina) were compared to positive and negative controls for their impact on yields of bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and pigeon pea (Cajanus cajan) crops and the abundance of key indicator pest and predatory arthropod species. Analysis of field trials showed that pesticidal plant treatments often resulted in crop yields that were comparable to the use of a synthetic pesticide (lambda-cyhalothrin). The best-performing plant species were T. vogelii, T. diversifolia, and L. javanica. The abundance of pests was very low when using the synthetic pesticide, whilst the plant extracts generally had a higher number of pests than the synthetic but lower numbers than observed on the negative controls. Beneficial arthropod numbers were low with synthetic treated crops, whereas the pesticidal plant treatments appeared to have little effect on beneficials when compared to the negative controls. The outcomes of this research suggest that using extracts of pesticidal plants to control pests can be as effective as synthetic insecticides in terms of crop yields while tritrophic effects were reduced, conserving the non-target arthropods that provide important ecosystem services such as pollination and pest regulation. Thus managing crop pests using plant secondary metabolites can be more easily integrated in to agro-ecologically sustainable crop production systems.

Yield Response of Intercropped Soybean and Maize Under Rhizobia (Bradyrhizobium japonicum) Inoculation and P and K Fertilization

ABSTRACT A 2-year trial was carried out at the Tanzania Coffee Research Institute (TaCRI) farm in northern Tanzania. The aim was to assess the response of soybean and maize yield attributes to cropping systems, rhizobia inoculation, and phosphorus (P) and potassium (K) fertilization. The study was laid out in a split-split plot design replicated thrice. The statistical analyses were performed using the 3-way analysis of variance in a factorial arrangement. The computation was performed using the STATISTICA software. The Fisher’s least significant difference (LSD) was used to compare the treatment means at p = 0.05 level of significance. The results showed that both cropping systems, rhizobia inoculation, and P and K fertilization significantly (p = 0.05) influenced most of the soybean yield parameters assessed in this study. Specifically, cropping systems significantly (p = 0.05) improved the number of pods per plant, biological yield, grain yield, and harvest index (HI) (2015 and 2016) of soybean. Rhizobia inoculation also significantly (p = 0.05) improved soybean yield attributes such as the number of pods, 100 seed weight, biological yield and grain yield of soybean (2015 and 2016), and HI in soybean (2015). P and K fertilization also significantly (p = 0.05) improved different yield attributes of soybean over the control. It was noted that increasing potassium from 20 to 40 kg/ha improved most of the soybean yield parameters relative to the control. Doubling of P from 26 kg to 52 kg/ha did not significantly change the soybean yield parameter. The doubled combined fertilizers did not significantly increase the yield parameters of soybean suggesting the use of a lower dose of combined fertilizers. Intercropping maize with rhizobia-inoculated soybean significantly improved maize yield compared with intercrop without inoculation. Monocropped maize gave relatively the same yield as those of maize intercropped with inoculated soybean. Fertilization with P and K also improved the yield attributes of maize over the control.

Pesticidal Efficacy of Four Botanical Pesticides on Survival, Oviposition and Progeny Development of Bruchid, Callosobruchus maculatus in Stored Cowpea, Vigna unguiculata

Cowpea (Vigna unguiculata) production is limited by various insect pests that attack and damage the crops both in the field and during storage. Cowpea bruchids, Callosobruchus maculatus are the major insect pests of cowpea which infest the cowpea grains in the field, and then carried into the store where the population builds up rapidly. Chemical insecticide application is one of the management options that has been used for many years to control the insect pests. However, due to the side effects associated with those insecticides, there has been a resurgence need of using botanical pesticides to control insect pests in the field as well as in storage. This review aims to increase an awareness of using selected botanicals (Tephrosia vogelii, Chenopodium ambrosioides, Tithonia diersifolia, Lippia javanica and Vernonia amygdalina) as the cheap, effective and environmental friendly insect pest management strategy against bruchids in stored cowpea. The bioactive compounds from these plants offer great potential of developing botanical pesticides against postharvest insects in stores. Review Article Mkenda and Ndakidemi; IJPSS, Article no. IJPSS.2014.12.001 1505

The effect of bud splitting on suppression of apical dominance and inducing multiple buds development in banana shoot tip cultures of cv. 'Yangambi' (AAA) in Tanzania.

Aims: The objective of this study was to investigate the effect of bud splitting technique on suppression of apical dominance and induction of multiple buds development in banana shoot tips ofcv. Yangambi. Study Design: The experiment was conducted in a completely randomized design, with three treatments each replicated ten times. OriginalResearch Article