Effect of triple-layer hermetic bagging on mould infection and aflatoxin contamination of maize during multi-month on-farm storage in Kenya

Field trials were conducted in small-scale farmers' grain stores in an aflatoxin endemic region to assess the effect of storing maize in triple layer hermetic (PICS™) bags on aflatoxin contamination. Shelled maize grain was purchased from farmers, and filled into PICS bags, woven polypropylene (PP) and jute bags and kept in the farmers' own stores for 35 weeks. Grain moisture content, total mould count and mould incidence levels were examined at onset and after every 7 weeks during the 35 weeks of storage. Aflatoxin contamination was examined at onset, and after 14, 28 and 35 weeks. Ambient temperature and r.h. in the trial site and in all the bags, as well as oxygen and carbon dioxide levels in the PICS bags were also monitored. Initial moisture content (m.c.) of maize varied from farmer to farmer and ranged between 12.4 and 15.0%. The m.c. of maize stored in PICS bags remained significantly higher (P < 0.05) than in PP and jute bags in the last 14 weeks of storage. Total mould count and aflatoxin contamination of maize stored at an initial m.c. < 13% and 13% ≤ m.c. ≤ 14% increased significantly in PP and jute bags but not in PICS bags. After 35 weeks, total aflatoxin of maize stored in the PICS bags at an initial m.c. < 13% and 13% ≤ m.c. ≤ 14% did not change where as it increased 5–8 folds in the PP and jute bags. Total mould count and aflatoxin contamination of maize stored at an initial m.c. > 14% increased profusely in the three types of bags. Our findings demonstrate that storing maize in PICS bags can prevent accumulation of aflatoxin in rural farmers' stores if grain moisture is <14%.     

Maintaining dryness during storage contributes to higher maize seed quality

Smallholder farmers in Pakistan store their seeds and grains in porous polypropylene (woven) and jute bags or in bulk. Seed stored in these containers is susceptible to fluctuating seasonal relative humidity and temperature, which promote mold and insect growth. The present study assessed the performance of Purdue Improved Crop Storage (PICS) bags for maize seed storage during a two-month period. Seed moisture content increased in polypropylene bags while it remained constant in PICS bags. No change in germination was observed in maize seeds stored in PICS bags while in polypropylene bags it was reduced in half when compared to the initial germination. Seed stored in polypropylene bags had higher insect damage with a weight loss of 35% while in PICS bags the infestation was minimal with a weight loss of about 3%. Higher aflatoxin contamination levels were observed in seeds stored in polypropylene than PICS bags. PICS bags are effective at preserving the dryness of maize seed in storage during high relative humidity conditions, which leads to maintenance of seed quality.     

Evaluating different hermetic storage technologies to arrest mold growth,prevent mycotoxin accumulation and preserve germination quality of stored chickpea in Ethiopia

Chickpea is an economically important pulse produced by millions of smallholder farmers as a source of food, income and nutrition in Ethiopia. Mold infection and mycotoxin production can potentially lead to significant losses of chickpea during storage. Under laboratory conditions we tested comparative effects of hermetic and traditional storage structures on mold infection, germination and mycotoxin levels of chickpea. Purdue Improved Crop Storage (PICS) bags, Super GrainPro (SGP) bags, and small metal bins were compared to the traditional and popularly used chickpea storage structures such as polypropylene (PP) bags and jute bags over a six-month storage period. Oxygen and carbon dioxide levels, chickpea temperature and moisture, seed infection with molds and percentage germination and mycotoxins levels were determined every two months for six months. In PICS bags, SGP bags and metal bins chickpea temperature and moisture changed very little during storage, whereas in jute and PP bags significant temperature and moisture increases were observed. Oxygen levels in PICS and SGP bags decreased from 20% to 8–10% in six months and carbon dioxide levels increased from 0.4% to 10% in PICS bags and from 0.1% to 17% in SGP bags. In jute and PP bags, oxygen levels were around 20% but carbon dioxide levels increased from 0.05% to 0.1–0.2%, perhaps due to mold activity. Mold infection decreased over time in chickpea stored in PICS bags, SGP bags, and metal bins, and seed germination was high (82–92%). Mold infection increased and seed germination decreased in chickpea stored in jute and PP bags. Increases in levels of aflatoxin, fumonisin, deoxynevalenol, and ochratoxin were observed only for chickpea stored in metal bins, and in jute and PP bags. Our study showed that PICS and SGP bags can effectively arrest mold growth, mycotoxin accumulation and preserve germination of chickpea during six months of storage.     

Impact of opening hermetic storage bags on grain quality,fungal growth and aflatoxin accumulation

Purdue Improved Crop Storage (PICS) bags are used by farmers in Sub-Saharan Africa for pest management of stored grains and products, including maize. These bags hermetically seal the products, preventing exchange with external moisture and gases. Biological respiration within the bags create an environment that is unsuitable for insect development and fungal growth. This study was conducted to determine the impact of routine opening of the storage bags for maize consumption on fungal growth and aflatoxin contamination. Maize with moisture contents (MC) high enough to support fungal growth (15%, 16%, 18% and 20%) was stored in PICS bags, which were opened weekly and exposed to humid conditions (85% RH) for 30 min over a period of 8 weeks and 24 weeks. Monitors indicated that oxygen defused into the open bags but did not reach equilibrium with the bottom layers of grain during the 30-min exposure period. Fungal colony forming units obtained from the grain surface increased 3-fold (at 15% MC) to 10,000-fold (at 20% MC) after 8 weeks. At both 8 weeks and 24 weeks, aflatoxin was detected in at least one bag at each grain moisture, suggesting that aflatoxin contamination spread from a planted source of A. flavus-colonized grain to non-inoculated grain. The results indicate that repeatedly breaking the hermetic seal of the PICS bags will increase fungal growth and the risk of aflatoxin contamination, especially in maize stored at high moisture content. This work also further demonstrates that maize should be properly dried prior to storage in PICS bags.     

Assessing Purdue Improved Crop Storage (PICS) bags to mitigate fungal growth and aflatoxin contamination

Storing maize in regions of the world without sufficient drying and storage capacity is challenging due to the potential risk of aflatoxin contamination produced by Aspergillus flavus. This study sought to determine if storage of maize in Purdue Improved Crop Storage (PICS) bags prevents mold growth and aflatoxin accumulation. PICS bags are a three-layer, hermitic bag-system that forms a barrier against the influx of oxygen and the escape of carbon dioxide. Maize conditioned at 12, 15, 18, and 21% grain moisture was inoculated with 50 g of maize kernels infected with fluorescent-marked strain of A. flavus. The grain was stored in either PICS or woven bags at 26 °C, and percent oxygen/carbon dioxide levels, fungal growth, aflatoxin, moisture content, and kernel germination were assessed after 1 and 2 months incubation. Maize stored in woven bags was found to equilibrate with the ambient moisture environment over both storage periods, while PICS bags retained their original moisture levels. Aspergillus flavus growth and aflatoxin accumulation were not observed in maize stored in any PICS bags. No aflatoxin B1 was detected in woven bags containing low-moisture maize (12 and 15%), but detectable levels of aflatoxin were observed in high moisture maize (18 and 21%). The percentage of oxygen and carbon dioxide within PICS bags were dependent on initial grain moisture. Higher carbon dioxide levels were observed in the bags stored for 1 month than for 2 months. High initial moisture and carbon dioxide levels correlated with low kernel germination, with the 18 and 21% treatment groups having no seeds germinate. The results of the study demonstrate that storage of maize in PICS bags is a viable management tool for preventing aflatoxin accumulation in storage.     

Effectiveness of grain storage facilities and protectants in controlling stored-maize insect pests in a climate-risk prone area of Shire Valley,Southern Malawi

Shire Valley is one of Malawi's most vulnerable areas to climate change (CC). In addition to other impacts, CC is expected to affect storage insect pest status, and the efficacy of grain storage facilities and protectants. On-farm grain storage trials were therefore conducted in Shire Valley to assess the performance of storage facilities and grain protectants against storage insect pests. Eight smallholder farmers hosted the trials in Thyolo and Chikwawa districts. Seven grain storage treatments were evaluated for 32 weeks during two storage seasons: Neem leaf powder (NM), Actellic Super dust (ASD), ZeroFly^® bag (ZFB), Purdue Improved Crop Storage bag (PICS), Super Grain Bag (SGB), hermetic metal silo (MS) and untreated grain in a polypropylene bag (PP). Insect pest populations and grain damage increased with storage duration and differed significantly between treatments (p < 0.05). Grain stored in hermetic bags (PICS, SGB) sustained significantly lower (p < 0.05) insect damage and weight loss compared to other treatments across sites and seasons. The hermetic bags also outperformed the other treatments in suppressing insect numbers. However, germination rates of undamaged grains stored in the hermetic storage facilities (MS, PICS, SGB) for 40 weeks were extremely low (<15%) compared to that of undamaged grains from NM treatment (53–58%) and the other treatments (>75%) at both sites. The hermetic MS, ZFB bags, ASD and NM treatments did not effectively protect grain from insect damage. High in-store mean temperature (35.6 °C) and high initial grain moisture content (13.7%) may have negatively affected efficacy of some treatments and seed germination. Tribolium castaneum survival in the MS requires further investigation. The hermetic storage bags (PICS, SGB) can be recommended for long-term maize grain storage (≥32 weeks) by smallholder farmers in Shire Valley and other similar climate change-prone areas in sub-Saharan Africa.     

Evaluating of hermetic bags for long-term storage of turmeric (Curcuma longa L.) rhizomes

Hermetical and traditional storage bags were evaluated for their effect on the postharvest storage of turmeric at laboratory conditions. The traditional Polypropylene (PP) woven bags and the jute bags were compared with Purdue Improved Crop Storage (PICS), Super Grainpro, Savegrain bags, and Ecotect bags. Every month, for eleven months, the levels of oxygen and carbon dioxide, moisture, insect damage, live insect count, weight loss of turmeric rhizomes were monitored. A slight change in moisture was observed for turmeric stored in PICS, Grainpro, Savegrain, and Ecotect bags. But, a significant decrease in moisture was observed for turmeric stored in jute bags. The levels of oxygen in PICS and Ecotect bags decreased from 20% to 8% while carbon dioxide content increased in PICS bags from 0.2% to 12% during the period of storage. In jute bags, the level of oxygen was approximately 19.3% but the level of carbon dioxide increased from 0.05% to 0.43% due to insect activity. In all hermetic bags, the risk of insects has decreased over time, and weight loss has also decreased as compared with jute bags. In Polypropylene woven and jute bags, damage by insects and weight loss increased during storage while the curcumin content reduced. Our study showed the effectiveness of PICS, Grainpro, Savegrain, and Ecotec bags in controlling insects and weightloss in turmeric rhizomes over the traditional bags. All the four hermetic bags performed well in long-term storage of turmeric rhizome and can be recommended.     

Comparative effects of hermetic and traditional storage devices on maize grain: Mycotoxin development,insect infestation and grain quality

A large-scale study was conducted to assess which of the five most accessible hermetic storage devices on the Kenyan market fulfill the needs of smallholder farmers by positively impacting three major areas of concern: insect infestation, grain quality, and mycotoxin (aflatoxin and fumonisin) contamination. Efficacy of two hermetic silos (plastic and metal) and three hermetic bags (PICS, GrainPro's GrainSafe™, and Super Grain) was directly compared to current maize storage in polypropylene (PP) bags under local environmental conditions using representative storage volumes during a 6-month storage period. Impact of maize grain stored at typical (∼15%) and recommended (<13.5%) moisture levels and potential efficacy losses through frequent interruption of the underlying hermetic principals was assessed. Hermetic storage significantly reduced the increase in aflatoxin compared to PP bags regardless of the moisture level of the grain. An <5% per month aflatoxin increase was achieved by three of the five devices tested: Metal silo, PICS and GrainSafe™ bag. A strong correlation between grain moisture, storage time and aflatoxin development was found in PP bags, but not in any of the hermetic devices. The same result was not obtained for fumonisin development in stored maize. The rate of Fumonisin increase was similar in all tested devices, including the polypropylene bags, and conditions. The periodic opening of the hermetic devices had no significant effect on the efficacy of the hermetic devices but the repeated disturbance of the PP bags led to a significant increase in aflatoxin levels. The maize weevil Sitophilus spp. was most commonly found with a total incidence of 72%. Grain storage under hermetic conditions reduced insect infestation, grain weight loss and discoloration. However, maize storage above recommended moisture levels led to a distinct odor development in all hermetic devices but not the PP bags. Hence, proper grain drying is a prerequisite for maize storage in airtight conditions.     

Safe storage of maize in alternative hermetic containers

Purdue Improved Crop Storage (PICS) bags have been developed and extended as a way to address grain storage issues faced by smallholder farmers in developing nations. A hermetic technology, PICS bags reduce insect damage to grain significantly while maintaining its quality for many months or longer. Farmers with varying and often small volumes of grain at harvest, may still benefit from alternatives to PICS bags for storing their grain. We evaluated plastic bottles, which may be hermetically sealed, for storing maize grain. Clean maize grain was stored for eight months in sealed and unsealed plastic bottles with half of these bottles being infested by maize weevil (Sitophilus zemais, Motschulsky). Oxygen levels in the bottles were monitored throughout the trial and grain was assessed for moisture content, insect damage, germination rate and insect population size when the study was terminated. Sealed bottles preserved grain quality significantly better than unsealed, infested bottles and as well as non-infested unsealed containers. Plastic soda bottles can be used as hermetic containers for safely storing grain.     

Performance of hermetic storage bags for maize grains under farmer-managed conditions: Good practice versus local reality

There are various types of grain storage bags available to farmers in tropical countries. However, these bags differ in price, quality, and reduced post-harvest losses due to insect pests and mould infestation. This study aimed to compare the effectiveness of three types of storage bags of Purdue Improved Crop Storage (PICS), Grain pro-super (GPS) and woven (WN) bags under assumed small farmer’s storage practices in the sub-tropical climatic conditions. The practice of weekly routine opening of the bags was compared with the recommended practice of keeping the bags closed for at least 3 months. Under laboratory experiment, insect population, moisture content, grain humidity, and temperature were measured at the weekly intervals while under farmer’s setting, moisture content (%) of maize and percentage of insect damage were measured after 3 and 6 months of storage at the farmer’s homestead. Considering the routine weekly opening effect, the PICS bag kept a low grain humidity average (56.6%) compared to the Grain pro-super bag (64.2%) and Woven bag (71.5%). The PICS bag reduced the insect population to an average of zero (0.4) compared to GPS (6.5) and the WN (14.8). Under farmer’s conditions, the mean difference in the percentage of insect damage between the PICS and GPS were insignificant (P > 0.05) at both 3 and 6 months of storage, and the insect damage throughout decreased with time. The results of this study indicate that PICS bag may support positively the practice of routine weekly opening compared to the GPS and WN in the sub-tropical climatic conditions.     

Impact of storage environment on the efficacy of hermetic storage bags

Small hermetic bags (50 and 100 kg capacities) used by smallholder farmers in several African countries have proven to be a low-cost solution for preventing storage losses due to insects. The complexity of postharvest practices and the need for ideal drying conditions, especially in the Sub-Sahara, has led to questions about the efficacy of the hermetic bags for controlling spoilage by fungi and the potential for mycotoxin accumulation. This study compared the effects of environmental temperature and relative humidity at two locations (Indiana and Arkansas) on dry maize (14% moisture content) in woven polypropylene bags and Purdue Improved Crop Storage (PICS) hermetic bags. Temperature and relative humidity data loggers placed in the middle of each bag provided profiles of environmental influences on stored grain at the two locations. The results indicated that the PICS bags prevented moisture penetration over the three-month storage period. In contrast, maize in the woven bags increased in moisture content. For both bag types, no evidence was obtained indicating the spread of Aspergillus flavus from colonized maize to adjacent non-colonized maize. However, other storage fungi did increase during storage. The number of infected kernels did not increase in the PICS bags, but the numbers in the woven bags increased significantly. The warmer environment in Arkansas resulted in significantly higher insect populations in the woven bags than in Indiana. Insects in the PICS bags remained low at both locations. This study demonstrates that the PICS hermetic bags are effective at blocking the effects of external humidity fluctuations as well as the spread of fungi to non-infected kernels.     

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.     

On-farm comparison of different postharvest storage technologies in a maize farming system of Tanzania Central Corridor

Seven methods for storing maize were tested and compared with traditional storage of maize in polypropylene bags. Twenty farmers managed the experiment under their prevailing conditions for 30 weeks. Stored grain was assessed for damage every six weeks. The dominant storage insect pests identified were the Maize weevil (Sitophilus zeamais) and the Red flour beetle (Tribolium castaneum). The moisture content of grain in hermetic conditions increased from 12.5 ± 0.2% at the start of storage to a range of 13.0 ± 0.2–13.5 ± 0.2% at 30 weeks. There was no significant difference (F = 87.09; P < 0.0001) regarding insect control and grain damage between hermetic storage and fumigation with insecticides. However, the insecticide treatment of polypropylene yarn (ZeroFly^®) did not control the insect populations for the experimental period under farmers' management. Grain damage was significantly lower in hermetic storage and fumigated grain than ZeroFly^® and polypropylene bags without fumigation. No significant difference in grain damage was found between airtight treatment alone and when combined with the use of insecticides. During storage, S. zeamais was predominant and could be of more economic importance than T. castaneum as far as maize damage is concerned. At 30 weeks, the germination rate of grain stored with insecticides or in hermetic storage (68.5 ± 3.6% to 81.4 ± 4.0%) had not significantly reduced from the rate before storage (F = 15.55; P < 0.0001) except in ZeroFly^®, also in polypropylene bags without treatment. Even though such bags did not control storage pests, farmers still liked this cheap technology. Hermetic storage techniques can be recommended to farmers without the use of insecticides provided they are inexpensive, and the proper application of technologies is ensured.     

Sorghum seed storage in Purdue Improved Crop Storage (PICS) bags and improvised containers

Seed storage is a major challenge for smallholder farmers in developing nations. Purdue Improved Crop Storage (PICS) bags effectively control the postharvest insect pests of cowpea and other crops. Farmers, encouraged by this success, have begun to expand the use of PICS bags for storing other crops. Little is known about how sorghum seed, one of these important crops, fares when stored under hermetic conditions. Accordingly, we stored sorghum seed for six months in either airtight containers (PICS bags or sealed plastic bottles) or open ones (woven polypropylene bags and open plastic bottles). Overall, sorghum seed stored in PICS bags and in sealed plastic bottles maintained its initial moisture level, germination rate and seed weight. Porous polypropylene bags and open plastic bottles lost moisture over six months. We conclude that sorghum seed can be safely stored in hermetic containers without any loss of quality for extended periods of time.     

The use and profitability of hermetic technologies for grain storage among smallholder farmers in eastern Kenya

Hermetic storage technologies (HSTs) have been disseminated in Sub-Saharan Africa (including Kenya) to reduce grain storage losses among farmers. We carried out a study in three counties in eastern Kenya to assess the use and profitability of HSTs among farmers. Data were collected from 613 farmers using a semi-structured questionnaire and Kobo Toolbox via android tablets. Results showed an increase in use of HSTs among farmers from 53.7% in 2015 to 91.2% in 2017. PICS was the most used hermetic bags by farmers (84%) in 2017. Majority of farmers (73.5%) received training in the use of HSTs from extension agents and agro-dealers. About 40% of respondents purchased additional (one to five) bags after their first experience using them. The quantity of grain produced made up about half of the farmer’s decision to store. The primary reason (87%) farmers used hermetic bags was the need to manage insect pests. Maize and beans were the most produced and most stored crops; but maize was the most stored in HST. Grain price seasonality showed a near doubling effect between the lean and harvest seasons. Estimates of the return on investments (ROI) ranged between 13 and 80% for all crops and maize stored in hermetic bags had the highest ROI. Awareness and trainings are key in increasing adoption and proper use of HSTs.     

Triple bag hermetic technology for controlling a bruchid (Spermophagus sp.) (Coleoptera,Chrysomelidae) in stored Hibiscus sabdariffa grain

We assessed the performance of hermetic triple layer Purdue Improved Crop Storage (PICS) bags for protecting Hibiscus sabdariffa grain against storage insects. The major storage pest in the grain was a bruchid, Spermophagus sp.. When we stored infested H. sabdariffa grain for six months in the woven polypropylene bags typically used by farmers, the Spermophagus population increased 33-fold over that initially present. The mean number of emergence holes per 100 seeds increased from 3.3 holes to 35.4 holes during this time period, while grain held for the same length of time in PICS bags experienced no increase in the numbers of holes. Grain weight loss in the woven control bags was 8.6% while no weight loss was observed in the PICS bags. Seed germination rates of grain held in woven bags for six months dropped significantly while germination of grain held in PICS bags did not change from the initial value. PICS bags can be used to safely store Hibiscus grain after harvest to protect against a major insect pest.     

Evaluation of postharvest preservation strategies for stored wheat seed in Ethiopia

Limited information exists on postharvest preservation strategies of stored wheat in Ethiopia. The present study was conducted to evaluate the effectiveness of on-the shelf postharvest storage strategies of stored wheat in the country. The experiment consisted of eight treatments; (1) metal silos, (2) Purdue Improved Crop Storage (PICS) bags, (3) Super GrainPro bags, (4) industrial filter cake dust applied to wheat in polypropylene bag, (5) plastic drums, 6) Triplex applied to wheat in polypropylene bag, 7) Triplex applied to wheat in plastic drum, and 8) polypropylene bag as control. Measurements of oxygen and carbon dioxide levels, live adults of insects per kg, percentage seed damage, and percentage of weight loss, germination and seedling vigor were determined every two months for six months. Results indicated that storage strategies such as PICS and Super GrainPro bags, filter cake, Triplex, and plastic drums led to a significantly lower live insect density compared to the control. Besides, Triplex and filter cake dust or use of hermetic bags also resulted in a significantly lower rate of seed weight loss (%) compared to the control. After six months of storage, means ± SD germination of seed from the polypropylene bag (control) had decreased to 68.0 ± 6.1% while wheat in all other storage strategies exhibited means ± SD germination capacity ranging from 92.0 ± 3.6% to 98.0 ± 1.0%. The present results demonstrate the potential of preserving stored wheat without relying on synthetic insecticides by using hermetic bags, filter cake, and Triplex, with advantages over traditional strategies used by smallholder farmers in Ethiopia. We recommend that hermetic bags, filter cake dust, and Triplex powder should be promoted for use by farmers for the postharvest preservation of their stored wheat.     

A time-saving method for sealing Purdue Improved Crop Storage (PICS) bags

Purdue Improved Crop Storage (PICS) bags were designed to reduce grain storage losses on smallholder farms. The bag consists of three layers: two high-density polyethylene liners fitted inside a woven polypropylene bag. Recently, farmer groups, development relief programs, and government food security agencies have shown interest in PICS bags for large-scale use. PICS bags are conventionally closed by a twist-tie (TT) method, which involves twisting, folding, and tying the lip of each layer individually with a cord. This is not only time and labor intensive, but also may affect the integrity of the liners. We evaluated three new bag closure methods: i) inner liner rolled onto itself and middle liner fold-tied (IR), ii) both liners folded together and tied (FT), and iii) both liners folded and tied separately (FS), along with the conventional twist tie (TT) method. The time to close partially or fully filled 50 kg-capacity PICS bags filled with maize grain was assessed. Results showed that FT was the most time-saving method, reducing bag sealing time by >34% versus the usual TT method. The average internal oxygen levels reached <2% within a week in bags containing grain highly infested with Sitophilus zeamais, while it remained >5% levels for less-infested bags. In both cases, insect population growth was suppressed. Oxygen depletion rates among tying methods remained the same regardless of the closure method used. When large numbers of bags need to be closed, the time-saving FT method is a good alternative PICS sealing method over the conventional twist-tie approach.     

Comparative performance of five hermetic bag brands during on-farm smallholder cowpea (Vigna unguiculata L.Walp) storage

Cowpea (Vigna unguiculata L. Walp) grain is an important source of protein for smallholder farmers in developing countries. However, cowpea grain is highly susceptible to bruchid attack, resulting in high quantitative and qualitative postharvest losses (PHLs). We evaluated the performance of five different hermetic bag brands for cowpea grain storage in two contrasting agro-ecological zones of Zimbabwe (Guruve and Mbire districts) for an 8-month storage period during the 2017/18 and 2018/19 storage seasons. The hermetic bag treatments evaluated included: GrainPro Super Grain bags (SGB) IVR™; PICS bags; AgroZ® Ordinary bags; AgroZ® Plus bags; ZeroFly® hermetic bags. These were compared to untreated grain in a polypropylene bag (negative control) and Actellic Gold Dust® (positive chemical control). All treatments were housed in farmers’ stores and were subjected to natural insect infestation. Hermetic bag treatments were significantly superior (p < 0.001) to non-hermetic storage in limiting grain damage, weight loss and insect population development during storage. However, rodent control is recommended, as rodent attack rendered some hermetic bags less effective. Actellic Gold Dust® was as effective as the hermetic bags. Callosobruchus rhodesianus (Pic.) populations increased within eight weeks of storage commencement, causing high damage and losses in both quality and quantity, with highest losses recorded in the untreated control. Cowpea grain stored in Mbire district sustained significantly higher insect population and damage than Guruve district which is ascribed to differences in environmental conditions. The parasitic wasp, Dinarmus basalis (Rondani) was suppressed by Actellic Gold Dust® and all hermetic treatments. All the hermetic bag brands tested are recommended for smallholder farmer use in reducing PHLs while enhancing environmental and worker safety, and food and nutrition security.     

Efficacy of phosphine and insect penetration ability in ZeroFly® bags

The deltamethrin incorporated woven polypropylene ZeroFly® storage bag is a promising novel technology for grain storage. However, if grain stored in ZeroFly bags gets infested and has to be fumigated using phosphine (PH₃), data on the effectiveness of such treatments are needed. Additionally, obtaining field data on ability of stored-product insect pests to breach ZeroFly bags would facilitate insect management. Therefore, efficacy of PH₃ in immature and adult Sitophilus zeamais (Motschulsky), Prostephanus truncatus (Horn), Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst) in experimental cages in maize stored in 100-kg polypropylene (PP), jute and ZeroFly bags was investigated. Post-fumigation mortality of adults was recorded after 7 d, and after 7 wk for immatures. The ability of either S. zeamais or P. truncatus to penetrate fabric of PP, jute and ZeroFly bags was assessed. Phosphine efficacy was good in all the three types of bags and resulted in complete mortality of adults and immatures of the four species tested. Sitophilus zeamais and P. truncatus were more successful in penetrating the PP bag fabric and on average made 84 and 780 holes per bag over a 4 mo-period, respectively; this was followed by jute with 37 and 614 holes. The ZeroFly bag was harder to breach and ≤3 holes per bag were made for both species. This study shows that PH₃ is highly efficacious in insects that infest maize stored in ZeroFly bags, and that these bags are not easily penetrated by stored product insect pests. Hitherto, ZeroFly bags are a good technology for storing grain that is not infested, and fumigation using PH₃ can be effectively conducted if infestation occurs. Therefore, ZeroFly bags can be incorporated in integrated stored product insect management (IPM) programs for bagged grains.