Insect-proof Screenhouse Research Articles

Aerodynamic properties of boundary layers along the roof of a large banana screenhouse under near-neutral atmospheric stability

Cultivation under screens and in screenhouses protects the crops from insects and extreme climate conditions and allows water saving. Previous studies considered the aerodynamic properties of boundary layers along two types of screens: a small shading thermal screen covering a hedgerow citrus orchard and a large 50-mesh, insect-proof screen covering a pepper plantation. To extend the previous results, a third type of screen was analysed in this study, a large flat-roof 17-mesh white woven shading screen covering a banana plantation. Vertical profiles of wind speed, air temperature, relative humidity, and friction velocity were measured by a lifting tower, and wind profiles were analysed under near-neutral atmospheric stability. Results show that normalised friction velocity, normalised roughness length, normalised zero plane displacement height and aerodynamic resistance are closer to the previous results of the large insect-proof screenhouse than those of the small shade net.

Optimization of Low-Tech Protected Structure and Irrigation Regime for Cucumber Production under Hot Arid Regions of India.

Water scarcity and climate variability impede the realization of satisfactory vegetable yields in arid regions. It is imperative to delve into high-productivity and water-use-efficient protected cultivation systems for the sustained supply of vegetables in harsh arid climates. A strenuous effort was made to find suitable protected structures and levels of irrigation for greenhouse cucumber production in hot arid zones of India. In this endeavor, the effects of three low-tech passively ventilated protected structures, i.e., naturally ventilated polyhouse (NVP), insect-proof screenhouse (IPS) and shade screenhouse (SHS), as well as three levels of irrigation (100%, 80% and 60% of evapotranspiration, ET) were assessed for different morpho-physiological, yield and quality traits of the cucumber in a two-year study. Among the low-tech protected structures, NVP was found superior to IPS and SHS for cucumber performance, as evidenced by distinctly higher fruit yields (i.e., 31% and 121%, respectively) arising as a result of higher fruit number/plants and mean fruit weights under NVP. The fruit yield decreased in response to the degree of water shortage in deficit irrigation across all protected structures. However, the interaction effect of the protected structure and irrigation regime reveals that plants grown under moderate deficit (MD, 20% deficit) inside NVP could provide higher yields than those obtained under well-watered (WW, 100% of ET) conditions inside IPS or SHS. Plant growth indices such as vine length, node number/plant, and shoot dry mass were also measured higher under NVP. The greater performance of cucumber under NVP was attributed to a better plant physiological status (i.e., higher photosystem II efficiency, leaf relative water content and lower leaf water potential). The water deficit increased water productivity progressively with its severity; it remained higher in NVP, as reflected by 20% and 94% higher water productivity than those recorded in IPS and SHS, respectively, across different irrigation levels. With the exception of total soluble solids and fruit dry matter content (which were recorded higher), fruit quality parameters were reduced under water deficit conditions. The findings of this study emphasize the importance of considering suitable low-tech protected structures (i.e., NVP) and irrigation levels (i.e., normal rates for higher yields and moderate deficit (-20%) for satisfactory yields) for cucumber in hot arid regions. The results provide valuable insights for growers as well as researchers aiming to increase vegetable production under harsh climates and the water-limiting conditions of arid regions.

Airflow temperature and humidity patterns in a screenhouse with a flat insect-proof screen roof and impermeable sloping walls – Computational fluid dynamics (CFD) results

Insect-proof screenhouses are commonly used to grow plants in warm climates. However, there is relatively little literature on their microclimate compared to greenhouses. This study presents computational fluid dynamics (CFD) results of airflow, temperature, and humidity ratio patterns in a screenhouse with a roof consisting of a large flat insect-proof screen and impermeable walls. First, vertical profiles of velocity, temperature, and humidity at the center of the screenhouse were obtained by 2D steady-state CFD simulations and validated by experimental results. Root mean square error (RMSE) values were used to measure the differences between the two. The lowest RMSE values among simulations with different turbulence models were 0.49 K, 1.26 g kg −1 , and 0.05 m s −1 (with the RNG turbulence model) for temperature, humidity ratio, and air velocity, respectively. The main deviation of the CFD results from the experimental results was observed with the air velocity in the upper region of the screenhouse. Inflow and outflow in the leeward and windward parts of the flat roof were observed, respectively. This resulted in large-scale airflow within the screenhouse opposite the outside wind direction at the canopy level. The results suggested that the leeward section of the screenhouse is warmer than the windward one and has a lower humidity ratio. Large-scale rotating airflow formed in the center of the screenhouse, close to the roof, a large area with a humidity ratio similar to ambient conditions. • CFD simulations are used to determine airflow, temperature and humidity patterns. • CFD and experimental results were in agreement except of velocity near screenhouse top. • Airflow within the canopy of an insect-proof screenhouse was opposite to wind direction. • From windward to leeward ends the temperature increased and humidity decreased.

Thermal Simulation of a Screenhouse Proposed for Fruit and Vegetable Production in the Lowlands of Panama

In developing countries, open field agricultural production is highly vulnerable to biotic and abiotic factors limiting crop productivity, generating economic losses and affecting food security. Therefore, one of the strategies that can improve these production systems is the implementation of the crops under cover technically adapted to the climatic and socioeconomic conditions of each region. The objective of this research was to analyze the thermal behavior and airflow patterns of an insect-proof screenhouse through computational fluid dynamics simulations using a 3D model. The results obtained for the multiannual monthly climatic conditions of a warm climate region in Panama showed that the airflow velocities inside the structure were lower between 76.8 and 80.2% with respect to the external velocity. The most critical scenarios showed temperature differences below 2℃ inside the screenhouse with respect to the outside. This value can be considered low as compared to the behavior of naturally ventilated greenhouses.

Two-Dimensional Numerical Study of the Microclimate Generated in Three Screenhouses for the Climatic Conditions of the Colombian Caribbean

Insect proof screenhouse is increasingly used in tropical countries with a warm climate, as this type of structure is more economical than greenhouses and gives farmers the opportunity to optimize their production systems. In this work we used an experimentally validated two-dimensional numerical model, the objective was to study the air flow patterns and the thermal and hygrometric behavior of three screenhouses differentiated in their geometric configuration of the roof area and under four (4) outside wind speeds. The results obtained allowed us to find that the airflow speed inside the screenhouse can be maximized with respect to the most critical scenario by 29% for a wind speed of 0.5 ms-1 and up to 292% for a wind speed of 3.0 ms-1, which generates reductions in the average temperature inside the structure of -0.2℃ (0.5 ms-1) and up to -2.2℃ (3 ms-1). While the relative humidity presented values of 1.6% and 6.3% higher for these same speeds.

Airflow patterns and turbulence characteristics above the canopy of a tomato crop in a roof-ventilated insect-proof screenhouse

Airflow patterns and turbulence characteristics inside a naturally ventilated screenhouse with tomato plants were experimentally investigated using 3D sonic anemometers simultaneously measuring air velocities at six horizontal positions in the space between the screened roof and the top of the canopy. The screenhouse had a flat roof and was ventilated through the roof only. Testing was carried out during about 3 weeks of crop development, under variable external conditions. The mean horizontal air velocity component above the canopy was generally lower than 0.20 Uoh (where Uoh is the mean horizontal external wind speed) and mostly in a direction opposite to the external wind. At low external windspeed, the airflow direction was not necessarily opposite to the wind direction. The vertical air velocity component was generally lower than 0.07 Uoh. The root mean square of the air velocity components, the turbulence intensity and the turbulence kinetic energy were much larger during the day than at night mainly due to the higher daytime effect of buoyancy and to a lesser extent due to the higher external wind speed. Spectral energy slopes of the velocity components were close to −5/3 during the day when wind speed was high. However, at night, when wind speed was low, the spectral energy slope of the velocity vector increased significantly. The integral length scales of turbulent eddies were greater in the horizontal than the vertical direction which is not surprising given the volume under consideration is bounded by the top of the canopy, the roof and the sidewalls.

Vertical profiles of temperature, humidity ratio and air velocity in different types of insect-proof screenhouse

Insect-proof screenhouses have become an important component of protected cultivation in mild climates. They are much cheaper than fully climate-controlled greenhouses, and enable the grower to achieve a reasonable yield at good quality. An experimental study was done to determine the performance of different structure shapes on vertical profiles of temperature, humidity ratio and air velocity in the central region of the houses. Effects of screenhouse height and roof shape (flat versus zigzag) are considered. It is shown that, in all types of screenhouse, the air temperature increased with height, while the humidity ratio decreased up to a certain point close to the screened roof, where the rate of decrease either became much smaller or even reversed, so that the humidity ratios increased with increasing height. Air velocity in the screenhouse center increased with height, and was in the range of 0.06-0.2 of ambient wind speed.

Application of the Flux-Variance Technique for Evapotranspiration Estimates in Three Types of Agricultural Structures

Irrigation of protected crops requires sound knowledge of evapotranspiration. Previous studies have established that the eddy-covariance (EC) technique is suitable for whole canopy evapotranspiration measurements in large agricultural screenhouses. Nevertheless, the eddy-covariance technique remains difficult to apply in the farm due to costs, operational complexity, and postprocessing of data, thereby inviting alternative techniques to be developed. The subject of this paper is the evaluation of a turbulent transport technique, the flux variance (FV), whose instrumentation needs and operational demands are not as elaborate as the EC, to estimate evapotranspiration within large agricultural structures. Measurements were carried out in three types of agricultural structures: (i) a banana plantation in a light-shading (8%) screenhouse (S1), (ii) a pepper crop in an insect-proof (50-mesh) screenhouse (S2), and (iii) a tomato crop in a naturally ventilated greenhouse with a plastic roof and 50-mesh screened sidewalls (S3). Quality control analysis of the EC data showed that turbulence development and flow stationarity conditions in the three structures were suitable for flux measurements. However, within the insect-proof screenhouse (below the screen) and the plastic-covered greenhouse, R2 of the energy balance closure was poor; hence, the alternative simple method could not be used. Results showed that the FV technique was suitable for reliable estimates of ET in shading and insect-proof screenhouses with R2 of the regressions between FV latent heat flux and latent heat flux deduced from energy balance closure of 0.99 and 0.92 during validation for S1 and S2, respectively.

English

A survey was conducted to determine the occurrence of sweet potato leaf curl virus (SPLCV) infecting sweet potato in Kenya. Vine cuttings of sweet potato were collected in 2011 from fields in Central, Western and Coastal regions of the country. The cuttings were grown in an insect-proof screen-house and scion grafted to Ipomoea setosa indicator plants. DNA was extracted from leaf samples of graft-inoculated I. serosa and tested for the presence of SPLCV by polymerase chain reaction (PCR) using degenerate and specific primers. The virus was detected in all the regions with incidence rates of 33, 17.0 and 2.6% from Western, Coastal and Central regions, respectively using specific primers. Coat protein gene AV1 from isolates collected from each region was sequenced and their comparison revealed >88.4% nucleotide identity. Phylogenetic grouping using nucleotide and amino acid sequences showed that four Kenyan isolates (Coast3, Central13, Coast15 and Western14) clustered together, while the other remaining five grouped a long with isolates from different parts of the world. The results reveal that Kenyan SPLCV isolates have a clear diversity and are also closely related with other isolates from different parts of the world. The wide distribution of the virus within the country means that urgent measures are needed to clean the farmers planting material to reduce possible losses incurred due to the presence of the virus.    Key words: Sweet potato leaf curl virus, coat protein gene, virus, sweet potato, nucleotide, amino acid.

Effect of roof height on microclimate and plant characteristics in an insect-proof screenhouse with impermeable sidewalls

An experiment was conducted to study the effect of structure height on air temperature and humidity, on air exchange rate and on transpiration and yield in an insect-proof screenhouse. Two houses with roof heights of 4 and 6 m, and impermeable polyethylene sheets on the sidewalls were examined. Air exchange with the outside environment took place only through the horizontal screened roof and tomato plants were grown in both houses. The results showed that the increase in screenhouse height from 4 to 6 m elicited almost no changes in daily mean air temperature, humidity ratio and consequently, in relative humidity within the canopy. However, it reduced by about 30% the airflow through the screenhouse and consequently the air exchange rate. Moreover, the increase in height did not elicit changes in crop transpiration, yield and plant development. Thus, it is concluded that in insect-proof screenhouses that are ventilated through the roof, there is no benefit in increasing structure height above the current common height of about 4 m.

Diurnal energy-partitioning and transpiration modelling in an insect-proof screenhouse with a tomato crop

An experiment was conducted to measure diurnal energy partitioning and evaluate use of the Penman–Monteith equation to estimate diurnal crop transpiration in an insect-proof screenhouse. The experiment was conducted in a flat-roof house, 4 m in height with a floor area of 745 m2, which was ventilated only through a screened roof. Measurements included global solar radiation, air temperature and humidity outside and inside the screenhouse. Net radiation, soil heat flux, transpiration and air velocity were measured inside the house and wind speed and direction were measured outside. Results showed variation in transmittance of global solar radiation through the screen in the roof throughout the day. At noon, global and net radiation inside the house were about 0.68–0.73 and 0.44–0.45 of the outside global radiation, respectively. Above the canopy, the ratio of net radiation to global radiation varied throughout the day as well. Latent heat flux due to transpiration was about 0.7–0.8 of net radiation most of the day, and the proportion increased in the late afternoon to about 1.4. Sensible heat flux was about 0.06–0.25 of external global radiation until early afternoon and became negative in the late afternoon. Soil heat flux was less than 3% of the external global radiation. The Penman–Monteith equation predicted daily transpiration within 4–6%. A net cooling effect of the screenhouse air was defined and it is shown that the difference between internal and external air temperature correlated well with that cooling effect.

Effect of leaf pruning on energy partitioning and microclimate in an insect-proof screenhouse with a tomato crop

An experiment was conducted to assess the effect of leaf pruning on energy partitioning and microclimate in a screenhouse with a tomato crop. The experiment was conducted in a flat-roof insect-proof screenhouse, 4 m in height with a floor area of 745 m 2 , which was ventilated only through the roof. Measurements included global solar radiation inside and outside the screenhouse, net radiation, soil heat flux, transpiration, air velocity and air temperature and humidity. The results showed that leaf pruning in a tomato crop significantly affects energy partitioning in a screenhouse: it reduced transpiration at noon by more than 100%, increased soil heat flux by more than 200% and consequently increased sensible heat flux from crop to screenhouse air by nearly 70%. As a result of leaf pruning, air temperature increased slightly, but vapour-pressure deficit increased significantly. Furthermore, leaf pruning strongly reduced the gradients of temperature and vapour-pressure deficit in the air layer above the canopy at noon, resulting in a more homogeneous environment in the vertical direction. Finally, leaf pruning contributed to a higher air velocity within the canopy, especially at high wind speed.

Genetic control of maize resistance to corn stunt spiroplasma

The corn stunt spiroplasma (CSS) is transmitted by Dalbulus maidis leafhopper. The disease causes severe losses on maize production. One complete diallel genotype of two corn stunt resistant maize lines, and two corn stunt susceptible maize lines were tested by spiroplasma inoculation under insect-proof screenhouse condition, in order to elucidate the maize genetic control to this disease. The percentage of reduction on plant dry weight caused by the spiroplasma inoculation in relation to the dry weight average of the healthy plants, was calculated for each plant spiroplasma inoculated, to express maize resistance. The disease incidence for each treatment was represented by the percentage of plants with CSS symptoms. The disease severity was scored based on CSS symptoms severity, for each plant. Reductions on the dry weight were caused by the disease; the disease severity data showed a positive and strong correlation (r = 0.80). The statistical analyses indicated that genetic control of maize resistance to spiroplasma includes genes with additive effects and genes with dominance or epistatic effects, suggesting complex resistance inheritance. One line was better performing than all the others, reducing the disease damage, as well per se as in crosses.

Witches'-Broom Disease of Lime Affects Seed Germination and Seedling Growth But Is Not Seed Transmissible

Witches'-broom disease of lime (WBDL), caused by 'Candidatus Phytoplasma aurantifolia', has devastated many Mexican lime orchards and is currently a threat to lime production in neighboring provinces of southern Iran. Several reports have suggested transmission and spread of WBDL phytoplasma through the seed of infected plants. In the present study, claims of seed transmission of this phytoplasma were examined. Fruit were collected from infected trees in the infested areas of Minab (Hormozgan Province) and from symptomless trees in noninfested areas. Lime seed from symptomless and witches'-broom-affected trees were sown in separate beds in an insect-proof screenhouse and the resulting seedlings were examined for phytoplasmal infection. Leaf, stem, and root samples were collected from both groups of seedlings every 3 months for 2 years and tested for WBDL phytoplasma using direct and nested polymerase chain reaction (PCR). Repeated PCR tests on the seedlings did not reveal the presence of phytoplasmal DNA. Likewise, symptoms of the disease were not observed on these seedlings after 2 years. PCR assays detected the phytoplasma in coats of some seed from infected trees; however, no excised embryos were positive for the phytoplasma. All positive PCR results were confirmed by restriction fragment length polymorphism assay. One-year-old seedlings derived from seed of noninfected plants appeared more vigorous in terms of height, number of leaves, and fresh weight of shoot compared with those from infected trees. The germination percentage, mean daily germination, peak value, and germination value were significantly higher for seed of fruit from noninfected trees and seed from fruit on asymptomatic branches of infected trees than those from fruit on symptomatic branches of infected trees.

Analysis of resistance to Yam mosaic virus, genus Potyvirus in white guinea yam (Dioscorea rotundata Poir.) genotypes

Resistance to Yam mosaic virus (YMV), genus Potyvirus was studied in 10 populations of selected white Guinea yam (Dioscorea rotundata). Plants of resistant genotypes: TDr 35, TDr 1621, TDr 93-1, TDr 93-32, TDr 95-107, TDr 93-23, and susceptible ones: TDr 87/00211, TDr 87/00571 and TDr 95-127 were screened for their reaction to the pathogen by symptom severity scoring scale of 1-5, and by quantifying virus multiplication by triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA). Controlled crosses were made among the genotypes within and between the groups according to reactions to the pathogen. The resultant F1 progenies were evaluated for the infection by disease symptom development and by TAS ELISA to detect a symptomless infection in an insect-proof screenhouse for the assessment of inheritance of resistance to YMV. A genetic analysis of the reactions of progenies derived from the D. rotundata genotypes to inoculation with YMV strongly suggests that resistance to the virus is a dominantly inherited trait. Segregation ratios obtained from the families indicate that at least two dominant genes are involved.

Aerodynamic properties of boundary layers along screens

Agricultural screens that cover crops modify the exchange of heat, mass and momentum between the crop and the atmosphere. The properties of the boundary layer above an insect-proof screenhouse, in which sweet pepper was grown, were investigated experimentally. A flat-roof screenhouse 110 m long, 60 m wide and 3.2 m high was used. Wind and temperature sensors were mounted above the screen 60 m to the east of the western edge of the house and 30 m north of its southern edge. Aerodynamic properties of the wind profile, namely the friction velocity, roughness length, zero-plane displacement and aerodynamic resistance were calculated and presented with respect to the stability of the surface layer above the screenhouse. It was shown that neutral and stable conditions, when compared with unstable conditions, act to inhibit turbulence, to reduce the roughness length, to displace the wind profile upwards to just above the screen, and to increase the aerodynamic resistance. The results were compared with previous data obtained for a small shading screen. Good qualitative similarity was obtained between the two sets of data and the causes of the quantitative differences between the two studies under unstable conditions were discussed.

Measuring and predicting evapotranspiration in an insect-proof screenhouse

This study addresses the current lack of accurate measurements and predictions of evapotranspiration below modern screening materials. Energy balance components, microclimatic and physiological parameters were measured in a 50-mesh insect-proof screenhouse cultivated with sweet pepper. A lysimeter-calibrated sap flow system and an eddy covariance system installed inside the screenhouse measured canopy transpiration and evapotranspiration, respectively. Sap flow (SF) and eddy covariance (EC) data showed good agreement ( R 2 = 0.95) and although EC exceeded SF by 9%, this was less than the standard error of inter-specific sap flow, supporting previous findings that mid-day soil evaporation was negligible. Screenhouse bulk resistance was inversely correlated with external wind speed and simple mass balance estimations gave reasonable values of evapotranspiration on a daily basis. A one-dimensional screenhouse model was derived, based on a modified Penman–Monteith equation incorporating an additional boundary layer resistance. The model, along with a greenhouse model, was used to calculate evapotranspiration of the screenhouse crop. Half hourly predictions of both models yielded good agreement with measured SF ( R 2 = 0.94–0.95). Daily crop water use, predicted with the greenhouse model was in better agreement with measurements than that predicted by the screenhouse model. Measured and predicted transpiration rates inside the screenhouse were approximately 1.8–2.1 mm day −1 during the most active stage of growth, while those simulated for a similar crop grown outside would be 4.5–5.3 mm day −1 on average. Model sensitivity analysis showed that reduced radiation and wind speed and modified vapour pressure deficit were the main factors influencing transpiration. Calculations of the decoupling factor Ω suggest that the screenhouse evaporative climate is predominantly “decoupled”.

Incidence of Viruses Infecting Sweetpotato in Tanzania.

A survey for incidence of sweetpotato viruses was carried out in the three sweetpotato-producing districts (Bukoba, Misungwi, and Tarime) in the Lake Victoria basin and in the Indian Ocean coastal zone (Bagamoya on the mainland and Unguja on Zanzibar Island) in Tanzania in March and April 2003. A total of 170 plants from 43 sweetpotato fields were collected, established in an insect-proof screenhouse, and tested for viruses by nitrocellulose membrane enzyme-linked immunosorbent assay (NCM-ELISA). Scions from symptomless plants were grafted onto Ipomoea setosa, a nearly universal indicator plant for sweetpotato viruses, and leaves were tested by NCM-ELISA. Results were confirmed in several seropositive plants by cloning and partial sequencing of the viruses. Sweet potato feathery mottle virus (SPMFV), Sweet potato mild mottle virus, Sweet potato chlorotic stunt virus (SPCSV), and Sweet potato chlorotic fleck virus were detected serologically in single or mixed infections. Frequencies of occurrence of these viruses as determined by serological detection showed SPMFV to be the most prevalent virus in all the surveyed districts. Our study revealed a higher incidence and diversity of viruses in the Lake Victoria basin compared with the Indian Ocean coastal area. These results represent the first survey for sweetpotato viruses in Tanzania using accurate detection methods.

Identification of resistance to Yam mosaic virus (YMV), genus Potyvirus in white Guinea yam ( Dioscorea rotundata Poir.)

Yam mosaic virus (YMV), genus Potyvirus; family Potyviridae is the most important virus infecting Dioscorea spp. in the tropics. It induces a variety of symptoms ranging from mild mosaic on leaves of infected plants to stunted growth. Field and laboratory studies were conducted in Nigeria to identify Dioscorea rotundata genotypes that are resistant to YMV. A total of 24 D. rotundata varieties were evaluated in the field under natural infection conditions at four locations in Nigeria during 1998 and 1999 planting seasons, and also in an insect-proof screenhouse using mechanical inoculation and vector transmission. The plants in the field were individually scored for virus symptom severity, while those in the screenhouse were indexed for YMV at 6, 8 and 10 weeks after inoculation by triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA). Analysis of the symptom severity scores showed highly significant differences ( P<0.01) among the genotypes. Varieties TDr 1621, TDr 1640, TDr 35, TDr 2224 and TDr 93-48 were identified as resistant to field infection by yam viruses based on their low symptom severity scores (<2 on a 1–5 scale). In the screenhouse evaluation by mechanical and vector transmission only TDr 1621, TDr 1640, and TDr 93-48 remained free from YMV infection confirming resistance to YMV in these varieties.

RT-PCR EVIDENCE OF THE NON-TRANSMISSION THROUGH SEED OF PLUM POX VIRUS STRAINS D AND M

Twelve different apricot selections and six peach varieties naturally infected with Plum pox virus (PPV) groups D and M, respectively, were used to investigate the role of seeds in the epidemiology of the virus. All plants were PPV-positive in IC-RT-PCR and the isolates were characterized by restriction analysis of amplicons with RsaI restriction and analysis of coat protein migration in 15% SDS-polyacrylamide gel, followed by Western blotting. The presence of PPV was checked on fully ripe seeds, germinating seeds and seedlings. One half of the apricot seed stock was analyzed by ELISA and IC-RT-PCR, separating cotyledons, also containing the embryo, from seed coats. The virus, in both species, was mainly localized in seed coats, but cotyledons were also infected. Seeds of the other half of the stock were germinated and maintained in an insect-proof screenhouse for over 3-years (apricot seedlings) or over 6 months (peach seedlings). Seedlings never showed symptoms and were found PPV-negative by molecular assays. The conclusion was that seeds have no role in PPV-M and PPV-D epidemiology.