Stored Sorghum Research Articles

Identification and Prevalence of Fungal Species in Stored Sorghum Grains Surveyed at Bodija and Oyo Town Markets in Oyo State and Ikire and Iwo Town Markets in Osun State, Western Nigeria

This study investigated the identification and prevalence of fungal species in stored sorghum grains surveyed at Bodija and Oyo town markets in Oyo State and Ikire and Iwo town markets in Osun State, Western Nigeria using appropriate standard methods. Six distinct fungal species were isolated from the sorghum grains and identified through macroscopic and microscopic examination. These species included Aspergillus flavus, A. niger, A. tamarii, A. terreus, Fusarium sp., and Rhizopus stolonifer. The prevalence of fungal contamination was found to be higher in the markets of Oyo State compared to those in Osun State. Additionally, Aspergillus flavus and A.niger were the most prevalent fungal species, while Rhizopus stolonifer was the least prevalent.

The distribution of insect pests and the associated loss of stored sorghum in the Kena district of Konso Zone, South-Western Ethiopia.

Sorghum is a staple crop grown in the poorest and most food-insecure regions of Ethiopia. But storage insect pests are its key constraints that have been causing considerable loss. Accordingly, an assessment of the prevalence of insect pests and the associated loss of sorghum stored under farmers' traditional storages was done in randomly selected major sorghum-growing kebeles of Kena District using a nested design between November 1, 2019 and December 30, 2020. It was conducted through the sampling of one kg of grain from a total of 360 randomly selected farmers' storages. Pests' abundance was determined by dividing the total number of individual species by the total number of samples. A count and weight method was used to estimate percent grain damage and weight loss by pests. Sitophilus zeamais, Sitophilus oryzae, Sitotroga cereallella, Tribolium castaneum, Tribolium confusum, Cryptolestes ferrugineus, Cryptolestes pusillus, Rhyzopertha dominica, and Plodia interpunctella were the pests identified from grain samples. When compared to mid-latitude, where they were found in the range between 2.36± 0.21 and 17.50±0.98 mean number of species, all of these pests had a considerably (p < 0.05) larger distribution in low-land kebeles, where they predominated in the range between 5.44±2.00 and 23.61±1.75 amean number. During the nine-month storage period, the degree of pest infestation, percentage of grain damage, and weight loss were significantly (p < 0.05) higher in the bamboo bins when no management measures were implemented in the mid-land and low-land kebeles, respectively, than in the barn. Consequently, bamboo bin storage was considered ineffective for sufficient sorghum grain protection against pests and the associated loss over a longer storage period. But barn storage and the use of cultural pest management practices performed better in protecting stored sorghum from pests. Therefore, improving the bamboo bin storage method is needed to improve its grain protection efficacy.

Insect Pests and Diseases in Stored Sorghum (Sorghum bicolor L.) and Maize (Zea mays L.) in West Hararghe, Ethiopia

The presence of major insect pests and microflora in stored sorghum and maize in West Hararghe, Ethiopia, poses a significant threat to food security and agricultural productivity, leading to postharvest losses and economic hardship for local farmers. This study aimed to evaluate and identify the main grain insect pests and diseases of stored maize and sorghum in West Hararghe, Ethiopia. The survey was carried out in five major sorghum and maize‐producing districts of the surveyed areas, namely, Mieso, Gemechis, Tullo, Anchar, and Oda Bultum. The results revealed that maize and sorghum grains stored in sacks, ground pits, markets, and hanging (maize cob) storage containers were infested with insect species: maize weevil (S. zeamais), Angoumois grain moth (S. cerealella), rice weevil (S. oryzae), Red flour beetle (T. castaneum), confused flour beetle (T. confusum), and Lesser grain borer (R. dominica). The mean levels of major insect pest infestations and associated percentages of grain damage, weight loss, and germination loss were recorded across all traditional storage systems, including sacking, marketing, hanging or maize cob, and ground pit storage methods. The highest absolute frequency and relative frequency of F. oxysporum (14.53%), followed by A. flavus (13.08%), on maize seeds were recorded in the agar plate test. A total of eight species of fungi, including Fusarium species, A. parasiticus, and A. niger, were identified using the blotter and agar plate method. The incidence of fungal diseases was markedly high (98.33%) in maize grain stored in the Anchar district, followed closely by grain stored in the market in the same district, recording 98.33%. Therefore, it is recommended that further confirmatory identification using molecular tools be conducted to develop novel management strategies for these insect pests and diseases.

PSXIII-19 Feeding One-Year Storage Sorghum Silage Base Diets: Effects of Grain Processing on Performance of Backgrounding Beef Cattle

Abstract The aim of the experiment was to evaluate the effect of feeding a one-year stored sorghum silage (SS), grain processed or not at harvest, on ADG, DMI and feed efficiency (FE) of beef heifers. A total of 96 Angus heifers were used in a completely randomized design with 6 pens/treatment of 8 heifers per treatment. Mixed model of SAS was used, and the model included the fixed effect of treatment: SS processed (PRO) or not (NPR), with initial BW used as covariate. Significance was declared at P &amp;lt; 0.05. A dual-purpose sorghum (ADV2450IG, Advanta seeds, Irving, TX) was harvested (Claas Jaguar 930, Harsewinkel, Germany) at the late-dough stage of grain maturity and PRO or NPR were obtained with a specific SS cracker (196 mm rolls of 125 teeth each, 40% speed differential, 1.1 mm roll gap). Each treatment was chopped at 15 mm theoretical length of cut and ensiled in polyethylene ag-bags (60 m long and 2.74 m diameter), for 388 d until starting the feeding trial. Two backgrounding diets containing (DM basis) 90.5% SS either PRO or NPR (31.4±1.4% grain content on average), 6.5% soybean meal (expeller) and 3% supplement (ROC90, Provimi, Argentina) were offered for a 12 d of adaptation and 60 d of experimental period. Diets were adjusted daily to a score of 0.5, using the SDSU 4-point bunk scoring system, and samples were taken for analyses. Initial, middle and final BW was measured, while DMI was calculated from differences between DM offered and refused within each pen (Table). In conclusion, feeding sorghum silage stored for 388 to 460 d, and either grain processed or not, resulted in similar ADG and FE when used as the base of the diet of backgrounding beef heifers.

PSXIII-18 Feeding One-Year Stored Sorghum Silage: Effects of Grain Processing on Intake and Apparent Total Tract Digestibility of Backgrounding Beef Heifers

Abstract This study evaluated the effect of feeding sorghum silage after one-year of storage (SS) based diets, on dry matter intake and nutrient digestibility of beef cattle. A dual-purpose sorghum (ADV2450IG, Advanta seeds, Irving, TX) was harvested (Claas Jaguar 930, Harsewinkel, Germany) at the late-dough stage of grain maturity and processed (PRO) or not (NPR) with a specific SS cracker (196 mm rolls of 125 teeth each, 40% speed differential, 1.1 mm roll gap). Whole-plant was chopped at 15 mm and ensiled in polyethylene ag-bags (60 m long and 2.74 m diameter), for 388 d until the beginning of a 60 d-performance trial which was followed by the digestibility trial. From a performance trial with eight heifers/pen, and 12 total (six per treatment), one heifer (13.5 ± 1 mo and 259,4 ± 38 kg of BW) by pen was randomly selected for the digestibility trial. Two backgrounding diets containing (DM basis), 90.5% SS either PRO or NPR, 6.5% soybean meal (expeller) and 3% supplement (ROC90, Provimi, Argentina); continued to be offered ad libitum for an extra 3 d of adaptation while feed and feces were collected the next 4 d. Feed was individually offered once daily, and orts were collected the following day. Fecal samples were collected twice daily and apparent total tract digestibility (TTD) was determined using uNDF240h as a marker. Data were analyzed as a completely randomized design using pen as the experimental unit, and initial BW as a covariate. No differences among treatments were detected for DM, OM, NDF, ADF, CP and starch intake (P &amp;gt; 0.35). No effects of treatment were observed (P &amp;gt; 0.40) for DM, OM, NDF, ADF, CP and starch TTD. In conclusion, no effects of processing on apparent total tract digestibility were detected when feeding a one-year stored sorghum silage to backgrounding beef heifers.

Studies on the Control of Mycotoxin Producing Fungi Isolated from Sorghum Sold in Bida, Niger State Nigeria

Sorghum is an important crop in Africa including Nigeria, Mali and Niger. Fungi contaminate grains including sorghum with fungal poisonous secondary metabolites called mycotoxins. The objectives of this study are the isolation of fungi associated with sorghum in storage and assay for the presence of mycotoxins in stored sorghum. Data obtained showed that stored sorghum used in this study contains Rhizopus stolonifer, Aspergilus oryzae, Aspergilus flavus, Aspergilus niger, Aspergilus solani, Aspergilus terreus and Fusarium oxysposum. Rhizopus stolonifer and Fusarium oxysporum produced zearalenone while Aspergillus oryzae, Aspergillus niger, Aspergillus solani and Aspergillus tereus produced aflatoxins B1. Fumanisin B1 and aflatoxinB1 were produced by Aspergillus flavus. Alium sativum and Zingiber officinale exhibited antifungal activity against the test fungi. This research work will provide a long term economic impact in reducing mycotoxicoses which are acute and chronic toxic diseases caused by mycotoxins. The findings will also serve the purpose of alerting consumers on the dangers of consuming poorly stored sorghum.

Identification of Aspergillus Fumigatus using Molecular Techniques

Plant pathogenic fungi belong to the Kingdom Fungi comprising of over 100,000 registered species grouped into about 4,300 genera. Many of these fungi infect a variety of cereals particularly stored condition. A study was conducted to evaluate the occurrence of Plant pathogenic fungi associated with stored Sorghum vulgare grains. The fungal was subjected to the fungal load for exact identification using the molecular biology technique. The fungal isolates were isolated from the collected grains. Results revealed that Genus Aspergillus fumigatus was the most frequent isolate which are known to produce Aflatoxins. A combination of many different isolates was present on the grains. The molecular identification method using Polymerase Chain Reaction (PCR) helped in the identification of fungi at the species level with precision and in the least possible time. In conclusion, the isolated species were identified morphologically as Aspergillus fumigatus. The fungal samples were then identified through molecular techniques by DNA sequencing which was identified as Aspergillus fumigatus. The molecular techniques used in this study, has added great benefits to the process of distinguishing between similar species of fungi in comparison with the classical techniques. Furthermore, there is a need for having a National Level, Germplasm collection centre and detailed database of all the naturally occurring post-harvest Plant pathogenic fungi for easy intervention and timely overcoming of situations in case of any emergency.

Efficacy of some botanical powders against rice weevil, Sitophilus oryzae infesting sorghum seed under storage conditions

The present studies were undertaken to evaluate the efficacy of some botanical powders against rice weevil infesting stored sorghum seed. In all twelve treatments and one untreated control were used. The bark powder of C. zeylanicum was found to be the most effective treatment amongst all the botanical powders, recording 100% adult mortality, while A. calamus used as standard check recorded 92.25% mortality. The seed powder of A. squamosa (92.74%) and A. Indica (85.33%) also gave better protection. Data recorded on percent weightloss was also minimum in C. zeylanicum (1.45%) followed by A. Squamosa C1.74%) and A. calamus (1.78%) while untreated control showed 44.33% weight loss.

Potentiality of some botanical extracts as biopesticides against the maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae)

Laboratory studies were conducted to investigate the efficacy of some botanicals in the management of Sitophilus zeamais Motsch infesting stored sorghum. The selected plant species were Euphorbia balsamifera Aiton, Lawsonia inermis L. and Mitracarpus hirtus L. Chloroform leaf extracts of the botanicals applied at 6.25, 12.50, 25.00, 50.00 and 100.00 mg ml-1 were used to determine their effect on adult survival, the concentration of total body protein and inhibition of acetylcholinesterase enzyme (AChE) activity in the weevils at 30 ± 2 oC and 70 ± 5% R.H. The botanicals resulted in adult mortalities ranging from 10.00 ± 0.00 to 90.00 ± 5.77%, reduced body protein and significantly inhibited the activity of AChE in S. zeamais. The botanicals tested could serve as biopesticides in the management of S. zeamais infesting sorghum in the storage.

Survey of storage insect pests and management of rice weevil, Sitophilus oryzae, using botanicals on sorghum (Sorghum bicolor L.) at Jawi District, Northwestern Ethiopia

Storage pests are the main cause of crop losses. This study was carried out to assess the status of storage insect pest infestation and evaluate the efficacy of botanicals for the management of rice weevil at Jawi District, Ethiopia. A cross-sectional study was conducted to assess storage insect pest infestation. Botanical insecticides were evaluated against Sitophilus oryzae. The treatments were arranged using completely randomized design and replicated three times. Data were collected through questionnaire and experiment and analysed using SAS version 9.0. The result of the study showed that the most important insect pests of stored sorghum were S. oryzae (57%), maize weevil 17% and other pests were 26% and 100% store infestation were recorded. The species of storage insect pests identified were rice weevil, maize weevil, angoumois grain moth, flour beetle, flat grain beetles and saw-toothed grain beetle. The average grain weight loss was 13.63%, physical grain damage 7.22%, germination speed index of 46.36% and germination percentage of 68.75% were recorded. Experimental results revealed that all treatments were exhibited significant differences in mortality rate against S. oryzae. Efficacy of botanical revealed that neem seed powder (50.70%) and garlic (53.33%) were significantly superior in efficacy against S. oryzae after 28th days of exposure. Neem leaf powder, Mexican tea, orange peel and ginger gave moderate mortality rate of 48.55, 26.11, 36.87 and 41.65, respectively, compared with the control. All botanicals have the potential F1 S. oryzae reduction effect. The highest F1 reduction was recorded in neem seed powder (73.14%), neem leaf powder (72.54%) and garlic (66.94%). The highest mean germination of 70, 63.33 and 61.33% were recorded from neem seed powder, garlic and neem leaf powder exposed seeds, respectively. Neem seed powder, garlic and neem leaf powder can be suggested as management options of S. oryzae in storage condition.

Phytochemical and insecticidal properties of some botanical extracts against the lesser grain borer, Rhyzopertha dominica F. (Coleoptera: Bostrichidae)

Experiments were conducted in postgraduate laboratory of the Department of Biology of Umaru Musa Yar’adua University, Katsina (UMYUK) Nigeria, to analyze phytochemical properties and assess insecticidal effects of acetonic leaf extracts of Euphorbia balsamifera, Lawsonia inermis and Mitracarpus hirtus against Rhyzopertha dominica F. To analyze the phytochemicals of the test plants, preliminary tests were conducted to determine secondary metabolites while Gas Chromatography Mass Spectrum (GC-MS) was carried out to identify various active compounds present in the botanical extracts. Effects of the treatments on adult mortalities against R. dominica, adult emergence and grain weight losses were also determined. To determine percentage mortalities of R. dominica at 7 days after treatment (DAT), acetonic extracts of the botanicals at the concentrations of 6.25, 12.50, 25.00, 50.00, 100.00 mgml-1 and permethrin powder at 11.20 mg/20 g were applied to 20 g of sorghum grains in different plastic bottles. None of the extracts or permethrin powder was added to the control. The experiment was arranged in a completely randomized design (CRD) and replicated three times. Findings of the study revealed the presence of alkaloids, carbohydrate, phytesterols, phenolic compounds, flavonoids, saponins, tannins and cardiac glycosides in the botanical extracts. The plant extracts resulted in adult mortality of R. dominica which ranged from 16.67 to 63.33% within 7 days after treatment (DAT). No adult emergence was observed in all the treated grains. Also, grain weight losses of the treated sorghum varied from 3.92 to 6.63%. Acetonic extracts of the botanicals could therefore be utilized to reduce R. dominica infestations in stored sorghum.

Seed Borne Fungal and Bacteria Pathogens Associated with Farmer-Stored Sorghum Seeds from Eastern, Coast and Nyanza Regions in Kenya

Sorghum ( Sorghum bicolor (L.) Moench) is an important cereal crop in Kenya. Access to good quality seeds is one of the constraints facing the small scale farmers in key areas growing sorghum. Good quality seed is an important factor for maintaining plant population and increasing crop yield to attain food security. One of the important aspects of good seed, besides high germination and purity is the absence of seed borne pathogens. In the present study, an experiment was carried out to identify fungal and bacterial pathogens associated with farmer-stored seeds of sorghum. The seeds were collected from farmers in Nyanza, Coast and Eastern regions, Kenya. The seeds were washed with sterile distilled water and sterilized in 1% Sodium hypochloride for 5 minutes, rinsed with sterile distilled water and dried using a blotting paper. The dried seeds were placed onto prepared Potato Dextrose Agar (PDA) and macerated seeds streaked on nutrient Agar (NA) on sterile Petri dishes and incubated at 23±2 0 C. The growing pathogens were sub-cultured on new media to make pure cultures. A segment of mycelia from the sporulating colonies in each pure culture was examined under a compound microscope and identified based on their morphology, colour and mycelia growth characteristics for fungi while bacterial identification was done using colony color and morphology on nutrient agar and biochemical tests. Ten fungal pathogens and one bacterium were identified growing on the sorghum seed samples. These were Acremonium spp ., Alternaria spp ., Aspergilus niger, Bipolaris cookie, Collectotrichum graminicola, Fusarium moniliforme, Fusarium solani, Fusarium ventrichosum, Phythium aphanidermatum, Rhizoctonia spp. and a bacterium Xanthomonas spp. It was observed that majority (32%) of the seed samples from Coast region were infected with bacteria Xanthomonas spp. Phythium. aphanidermatum was the most prevalent fungal pathogen detected on seed samples from Nyanza region with about 20% prevalence. Results showed that majority of the seed samples from all the regions were contaminated with various pathogens. This study highlights the need to create awareness to farmers on the use of proper production practices, storage facilities and conditions to improve the quality of stored sorghum seeds. Keywords : farmer-stored seeds, seed-borne pathogens, sorghum DOI: 10.7176/JBAH/10-18-06 Publication date: September 30 th 2020

Development of Rhyzopertha dominica (Coleoptera: Bostrychidae) on sorghum: Quality characteristics and varietal susceptibility

A white low polyphenol sorghum, a red-waxy starch sorghum, a red-tannin sorghum with moderate polyphenol levels, and a red non-tannin sorghum were evaluated for susceptibility to Rhyzopertha dominica (Fab.) (Coleopter: Bostrychidae), the lesser grain borer. Density levels of 0 (untreated controls), 10, 20, or 30 mixed-sex adults were exposed on 100 g replicates of each of the varieties and removed after two weeks. Progeny production and physical damage were evaluated on each variety, along with quality characteristics such as moisture content, protein, starch, phenolic content, and kernel vitreousity. Progeny production and physical damage varied with density level and variety, but was generally lowest on the red-waxy sorghum. At the density level of 30 parental adults more progeny were found in the red-tannin sorghum compared to the other varieties. Starch content, kernel vitreousity and hardness was lower in the red-tannin sorghum. Total phenolic content was 2–3x greater in the red-tannin sorghum compared to the other varieties, but the high phenolic content did not seem to affect R. dominica progeny production. Results suggest the insects bypassed the bran layer of the sorghum varieties to feed on the germ and endosperm. Results of this study could be used to further explore the relationships between kernel hardness, chemical composition, and susceptibility to stored product insects, and incorporate results into management programs for maintaining quality of stored sorghum and processed sorghum food by-products.

Species Composition and Status of Stored Sorghum Pests in Traditional Farmer’s Storages of Kena District of Koso Zone, Southern Ethiopia

Aim: To determine the species composition and status pests of stored sorghum under traditional storages of farmers in Kenna district of Konso Zone of Southern Ethiopia.&#x0D; Study Design: From peasant association, about three sub-localities were randomly selected and from each sub-locality, three villages were selected at random with using a nested design.&#x0D; Place and Duration of Study: Survey was conducted between 1, August to 27, December 2019 in four major sorghum growing peasant association of Kenna district of Southern Ethiopia.&#x0D; Methodology: The study on determination of the species composition and status pests of stored sorghum was made from of half kilogram of wheat grain sample taken from 720 stores of randomly selected representative farmer’s storages of four peasant associations using key of books related to stored product insects.&#x0D; Results: Fifteen arthropods species consisting of twelve primary and secondary pests and three natural enemies belonging to four insect orders with in nine families were recorded. Of which, nine species such as S. zeamais, S. oryzae, S. cerealella, T. castaneum, T. confusum, C. ferrugineus, C. pusillus, R. dominica and P. interpunctella, respectively were found to be the most abundant as they appeared between 3.47 and 19.44 individuals per 100 g of sampled grains. They were also found to be the most frequently occurring as they occurred in the range between 63.89 and 94.44% per 100 g of sample grain collected from survey site and had major pest status.&#x0D; Conclusion: The traditional methods and practices used by farmers were inefficient for providing adequate protection of their stored sorghum grain pests. Therefore, there is urgent need for designing effective management strategies against insect pest’s sorghum as well as improving the existing farmer’s traditional storage strictures in the survey site in order to reduce the loss of stored sorghum by insect pests and the associated food insecurity.

English

Entomocidal activity of ethanolic leaf extracts of four plant species namely Euphorbia balsamifera Aiton, Lawsonia inermis L., Mitracarpus hirtus (L.) DC. and Senna obtusifolia L. were evaluated in order to assess their protectant ability to stored sorghum against Sitophilus zeamais Motsch. The botanicals were applied to 20 g of sorghum grains at the rate of 25, 50 and 100 mgml-1, while no extracts was added to the control. Percentage repellency was recorded at 24 h after exposure (HAE) while adult mortalities of the weevils were obtained at 3 days after treatment (DAT). Adult emergence and grain perforations were recorded at 49 and 84 DAT, respectively. Repellency levels of the botanicals against S. zeamais ranged from 87.05 &plusmn; 0.45 to 100.00 &plusmn; 0.00%. Also, the ethanolic extracts resulted in high adult mortalities of the weevils in the treated sorghum grains. No adult emergence was recorded in grains treated with the botanical extracts. Highest (10.00 &plusmn; 2.04%) grain perforations among the treatments were observed in 25 mgml-1 of S. obtusifolia, while 2.50 &plusmn; 1.25% was the least in the highest concentration of E. balsamifera. Findings of the study have revealed that the selected botanicals could serve as stored sorghum protectants against S. zeamais infestations. Key words: Adult mortality, adult emergence, grain perforations, plant extracts, repellency levels, Sitophilus zeamais. &nbsp

Effects of PICS bags on insect pests of sorghum during long-term storage in Burkina Faso

The PICS bags, originally developed for cowpea storage, were evaluated for sorghum (Sorghum bicolor) preservation. Batches of 25 kg of sorghum grain were stored in 50 kg PICS or polypropylene (PP) bags under ambient conditions for 12 months and assessed for the presence of insect pests and their damage, seed viability and, oxygen and carbon dioxide variations. The grain was incubated for 35 days to assess whether any insects would emerge. After six months of storage, oxygen levels decreased in the PICS bags compared to polypropylene bags. After 12 months of storage, only two pests, Rhyzopertha dominica and Sitophilus zeamais were found in the PICS bags. However, in PP bags there were additional pests including Tribolium castaneum and Oryzeaphilus mercator and Xylocoris flavipes. Grain weight loss and damage caused by these insects in the PP bags were significantly higher compared to those stored in PICS bags. Germination rates of sorghum grains stored in PP bags decreased significantly while no changes were observed in grains stored in PICS bags when compared to the initial germination. After the incubation post storage period, there was a resurgence of R. dominica in sorghum grains from PICS bags but the population levels were significantly lower compared to polypropylene bags. PICS bags preserved the quality and viability of stored sorghum grains and protected it from key insect pests. The PICS technology is effective for long-term sorghum storage but the potential resurgence of insects in low-oxygen environment calls for further research.

Traditional storage pit, polota, for storing sorghum as a long-term survival strategy in Dirashe special Worenda, Southern Ethiopia

ABSTRACTSeventy percent of the African continent is categorized into arid and semi-arid zones with a harsh climate. As a result of difficulties in securing a reliable food supply, it is thus quite rare to see the accumulation of food in rural villages in Africa. On the other hand, the Dirashe people living in southern Ethiopia own traditional storage pits called “polota” that can store sorghum for several years. This study investigates how the people utilize polota in their daily lives in order to secure a sufficient supply of food at both the individual and community levels. Participant observation and interviews were conducted to ascertain the roles of polota, the management of crops, and the historical background of polota. Moreover, climate data were analyzed to understand the climate over a span from several years to several decades, as this has a great influence on food production. Ultimately, the polota enables the villagers to prepare for a year of harvest failure by strategically storing crops harvested in a year of large yield. Additionally, those who own a number of polotas voluntarily open them and share the stored sorghum with villagers during the time of food security.

Use of plant products as potential eco-friendly management alternatives for the control of rice weevil, Sitophilus oryzae in stored sorghum

Results revealed that toxicity of custard apple seed powder and cinnamon bark powder increased with an increase in dosage as well as an increase in the period of exposure to both the plant powders. Both the powders significantly reduced the number of rice weevil, Sitophilus oryzae adults. Amongst the two cinnamon powder was found more toxic than custard apple seed powder. The highest dosage (5%, w/w) showed more promise after 14 days and resulted in maximum mortality of S. oryzae.

Blanket application rates for synthetic grain protectants across agro-climatic zones: Do they work? Evidence from field efficacy trials using sorghum grain

Many smallholder farmers in sub-Saharan Africa rely on synthetic pesticides for protecting stored-grain. Recommendations on use of these grain protectants are typically based on “blanket” application rates which are fixed rates that are not varied according to grain type, pest range or agro-climatic regions. There are numerous anecdotal reports of storage pesticide failure or reduced efficacy from farmers. Might rising global temperatures be a contributory factor? Smallholder farmers are responding by over-applying pesticides, increasing the application frequency or switching to non-recommended pesticides; leading to a pesticide treadmill. Trials to determine the efficacy and persistence of five commercially-available synthetic pesticides applied at manufacturer's recommended rates on stored sorghum grain under contrasting climatic conditions were conducted in Mbire (mean temperatures of 32–42 °C and 30–50% rh) and Harare (18–32 °C; 42–75% rh) districts in Zimbabwe. Grain samples were collected at 8-week intervals throughout a 10 month period in the 2014/15 and 2015/16 storage seasons. The samples were analyzed for insect grain damage, weight loss, total number of storage insects by species and grain moisture content. Results showed significant differences in the performance of treatments (p < 0.001). Grain damage was consistently higher in Harare than in Mbire. Tribolium castaneum was the dominant pest in Mbire, while Sitotroga cerealella and Sitophilus oryzae were dominant in Harare. Tribolium castaneum populations were high in the Shumba Super dust® (fenitrothion 1% + deltamethrin 0.13%) treatment in Mbire, while S. cerealella was dominant in Super guard® (pirimiphos-methyl 1.6% + permethrin 0.4%) and Actellic Gold dust® (pirimiphos-methyl 1.6% + thiamethoxam 0.36%) treated grain in Harare. Grain moisture content varied with ambient conditions, and was high in treatments with high insect pest levels. The results show that differences in climatic conditions influence insect pest species dynamics and response to pesticide treatments. Storage pesticides are not equally effective across different climatic conditions; thus more context-specific application recommendations are required.

Repellency potential of some botanicals against the maize weevil, Sitophilus zeamais (Motschulsky, 1855) (Coleoptera: Curculionidae) in stored sorghum

Abstract Repellency of Euphorbia balsamifera, Lawsonia inermis, Mitracarpus hirtus and Senna obtusifolia along with permethrin powder against Sitophilus zeamais was evaluated in the laboratory at 28-32°C and 60-75% RH. The botanicals were applied as powders, methanolic, ethanolic and aqueous extracts at the rate of 2.5, 5.0 and 10.0 x 104 ppm per 20 g of sorghum grains, while the permethrin powder was applied at 0.056 x 104 ppm. Percentage repellency was recorded at 1, 6, 12 and 24 hours after exposure (HAE). All the botanicals were found to have a repellent effect against Sitopholus zeamais at all three concentrations. The highest (82.22 ± 2.22%) repellency among the botanical powders was exhibited by 10.0 x 104 ppm of Euphorbia balsamifera within 24 HAE. Methanolic leaf extracts were found to be more effective than the other formulations, causing total repellency against the weevils at 10.0 x 104 ppm of all the botanicals, while the activities of the aqueous extracts were the least repellent (41.37 ± 7.39 to 60.14 ± 1.64%) after 24 hours of exposure. The repellent activities of the botanicals decreased with increasing exposure periods for powders and aqueous extracts, and increased with increasing duration for methanolic and ethanolic extracts. The results showed that the botanicals were good repellents against Sitopholus zeamais and could serve as stored sorghum protectants against maize weevil infestation. Grains protected with these botanicals could be used as seeds for planting. Meanwhile, studies on the toxicity of these botanicals against higher animals are recommended.