Photoselective Shade Netting Integrated with Greenhouse

ISHS International Workshop on Greenhouse Environmental Control and Crop Production in Semi-Arid Regions, Tucson AZ (C. Kubota and M. Kacira, eds.) Acta Hort. 2008 797: 75-80.

Photoselective Shade Netting Integrated with Greenhouse Technologies for Improved Performance of Vegetable and Ornamental Crops Yosepha Shahak1, Elazar Gal2, Yossi Offir2 and David Ben-Yakir3 1 Institute of Plant Sciences, ARO, The Volcani Center, Bet-Dagan, Israel 2 Polysack Plastics Industries, Nir Yitzhak – Sufa, Israel 3 Institute of Plant Protection, ARO, The Volcani Center, Bet-Dagan, Israel Keywords: colored shade-nets, light scattering, crop yield, pest control, protected cultivation Abstract Photoselective shade-netting is an emerging approach in protected cultivation. The photoselective net products are based on the introduction of various chromatic additives, light dispersive and reflective elements into the netting materials. They are designed to selectively screen various spectral components of solar radiation (UV, PAR, and beyond), and/or transform direct light into scattered light. The spectral manipulation is aimed to specifically promote desired physiological responses, while the scattering improves the penetration of the modified light into the inner plant canopy. Additional potential benefits relate to photoselective effects on plant pests, beneficial insects, or diseases. Studies of ornamental crops, traditionally grown in shade-net houses, revealed distinct responses to the Red, Yellow, Blue Grey and Pearl nets, compared with common black nets of the same shading factor. These include stimulated vegetative vigor, dwarfing, branching, leaf variegation, and timing of flowering. The photoselective netting concept was further tested in vegetable cultivation in either net-houses, or in combination with insect-proof nets or greenhouse plastic film covers. The Red and Pearl nets repeatedly increased the productivity of leafy crops, bell peppers and ornamentals, compared with each crop’s standard cover. Although the shade-net holes allow free passage of small pests, the rates of pest infestations and vector-borne viral diseases were affected by the color and reflectivity of the nets. For example, the incidence of an aphid borne cucumber mosaic virus disease was significantly lower under the Pearl (10 folds) and Yellow (3 folds) nets, compared to black nets. Whiteflies penetration and establishment was 2 fold lower under the Yellow net compared to the black net. The photoselective, light-dispersive shade nets provide a unique tool that can be further implemented within protected cultivation practices. INTRODUCTION The photoselective netting is an emerging approach, which introduces additional benefits, on top of the various protective functions of nettings. These nets are unique in that they both spectrally-modify, as well as scatter the transmitted light. The photoselective net products are based on the incorporation of various chromatic additives, light dispersive and reflective elements into the netting materials during manufacturing. The photoselective nets include “colored-ColorNets” (e.g. Red, Yellow, Green, Blue net products) as well as “neutral-ColorNets” (e.g. Pearl, White and Grey) absorbing spectral bands shorter, or longer than the visible range. The spectral manipulation is aimed at specifically promoting photomorphogenetic-physiological responses, while light

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scattering improves light penetration into the inner canopy (reviewed by Rajapakse and Shahak, 2007). Radiation use efficiency increases when the diffuse component of the incident radiation is enhanced under shade (Healey et al., 1998). In addition to its direct effect on the plants, the photoselective filtration of sunlight may also affect plant pests, beneficials and diseases. Some of the photoselective shade nets contain pigments known to attract whiteflies and thrips (i.e. yellow and blue). Therefore, crops grown under those nets could potentially be at a higher or lower risk for pest infestation. Covering greenhouses with films or screens containing UV absorbing additives is known to provide better protection against most pests, relative to standard cladding materials (reviewed by Antignus and Ben-Yakir, 2004). In this report we review the responses of numerous horticultural crops to photoselective netting, including crop performance, pest infestation, and some uses in combination with other covering materials. MATERIALS AND METHODS The photoselective shade nets and insect-proof screens were developed in collaboration with, and produced by Polysack Plastics Industries, Nir-Yitzhak, Israel under the trade mark ChromatiNets and OptiNets, respectively. Spectral properties of the various photoselective net products (light transmittance, scattering and reflectance) were previously described (Shahak et al. 2004a&b; Rajapakse and Shahak, 2007; Ben-Yakir et al., 2008). RESULTS AND DISCUSSION The photoselective, light-dispersive netting concept is being studied in a continuously growing number of crops. These include crops that were traditionally grown in shade-houses, open field, or greenhouses. Shade-Net Houses 1. Foliage crops. Photoselective netting was tested in foliage crops, traditionally cultured under black shade nets of 50-80% shading (e.g. Pittosporum variegatum, Fatsia japonica, Monstera deliciosa). Compared with black nets of the same shading factor (in PAR), the Red and Yellow nets were found to specifically stimulate vegetative growth rate and vigour, the Blue net caused dwarfing, and the Grey net specifically enhanced branching and bushiness, and also reduced leaf size and variegation in Pittosporum (Oren-Shamir et al. 2001; Shahak, 2008). The effects of the Blue, Yellow and Red nets result from their enriching/reducing the relative content of blue, yellow and red spectral bands of the transmitted light, and might be related to similar effects reported for photoselective films and artificial illumination (reviewed by Rajapakse and Shahak, 2007). The effects of the Grey net might relate to its distinct absorption in the IR range. 2. Cut flowers. Several cultivars of Lisianthus (Eustoma grandiflorum), sunflower (Helianthus annuus) and Trachelium were found to develop longer and thicker flowering stems under the Red and Yellow nets, while shorter under the Blue, compared with their equivalent black shade net. Additionally, the Red net induced shorter time to flowering in some species. The extent of responsiveness varied amongst the different species and cultivars (Oren-Shamir et al., 2003; Rajapakse and Shahak 2007). The highly dispersive Pearl net was recently reported to enhance branching of Myrtus communis pot plants, while in Crowea ‘Poorinda Extasy’ it increased the number of flowers per branch, compared with a black net of the same shading capacity (Nissim-Levi et al., 2008).

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3. Fruit trees. Low-shading photoselective netting of fruit tree crops (e.g. peach, apple, pear, table grapes) traditionally cultivated un-netted, revealed differential effects of the colored nets on orchards performances. The net-covering by itself was found to mitigate extreme climatic fluctuations, reduce heat/chill/wind stresses, enhancing photosynthesis and canopy development, compared with the un-netted orchards. On top of that, the photoselective, light-dispersive filtration of sunlight further affected the following traits in a differential manner, depending on the chromatic properties of each net. The photoselective responses include fruit-set, harvest time (early or late maturation), and fruit yield, size, color, internal and external quality (Shahak et al., 2004a&b; Rajapakse and Shahak, 2007; Shahak et al., 2008). 4. Vegetables. Bell pepper (Capsicum annuum) is commercially grown at the arid Besor area in Israel under shade nets of 30-40% shading for producing high-quality fruit, avoiding sunburns, and saving on irrigation. We have compared the traditional black shade nets with the Red, Yellow and Pearl nets for their effect on pepper productivity and quality. The spectra of transmittance of total light, and spectra of scattered (diffused) light under these nets is illustrated in Fig. 1A and 1B, respectively. Pepper cultivation under the colored shade nets increased productivity of 5 different cultivars tested during 3 successive years. Depending on the year and cultivar, the total fruit yields (in t/ha per season) under the colored nets were higher by 115%-135%, relative to the equivalent black shade net. The higher fruit yield resulted mostly from enhanced rates of fruit production, namely the number of fruits produced per plant (see Fig. 2A&B), while average fruit size was not significantly affected in most cases (not shown). Why is productivity increased? Air temperatures and relative humidity under the different nets did not differ from one another. Measurements of average leaf chlorophyll content, photosynthesis rate of exposed leaves, and canopy fresh and dry weight did not reveal significant differences either (data not shown). We speculate that the modification of light quality by the tested photoselective shade nets promotes fruit-set, and/or fruitlet survival rate. This might result from either the higher content of scattered/diffuse light under these nets compared with the equivalent black nets, or from the modified spectral composition, or both. The Pearl, Yellow and Red nets all transmit highly scattered light which is enriched in the green+red+far-red spectral range relative to the UV+blue (Fig. 1). Further studies are required to establish the hypothesis and mechanisms involved. Colored Shade Nets Integrated with Other Covering Materials Greenhouses and tunnels covered by plastics films often require additional shading for reducing the heat load. Below, we provide a few examples for substituting the traditional shading practice by photoselective shading. 1. Colored shade nets in film-covered tunnels. Lettuce (Lactuca sativa) grown in the west-Negev area of Israel in walk-in tunnels covered by clear plastic films plus 30% shading nets produced lettuce heads, which were 20-30% larger (‘Noga’), or 40-50% larger (‘Iceberg’), if the Red or Pearl nets were used instead of the equivalent Blue, black or Aluminet (reviewed in Shahak, 2008). In Almeria, Spain, the 30% Red shade net was found by the group of Fernández-Rodriguez to promote higher pepper and tomato yields, compared with the traditional white-wash (Shahak et al, 2004c). 2. Pepper in insect-proof-net houses. Winter pepper cultivation in 25-50 mesh insectproof houses in the Arava valley, Israel, requires supplemental 30% shading during the first month after planting (August), and again towards the end of the season. The Red net

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promoted early season fruit yield by 8-21% (depending on the year and cultivar), relative to the black, Grey or Blue nets, and induced an additional fruit cycle at the end of winter. 3. Rose cultivation in a greenhouse. Red nets of 30% shading which were applied inside greenhouses of roses (Rosa cultivars) covered by clear plastic films in Naivasha, Kenya, promoted the average stem length by ca 5 cm, and improved coloration in bicolor cultivars, as well as crop uniformity, compared with the common practice cover of the same shading capacity (not shown). Photoselective Shade Nets Differentially Affect Vegetable Pest Infestation As expected, whiteflies and thrips preferred landing on Yellow and Blue nets, respectively. Nevertheless, the number of pests trapped inside chambers or tunnels covered by these nets were similar to, or lower than the equivalent black net (Table 1). The number of whiteflies found on traps and plants under the Yellow net was 2-3 folds lower than under the black net (Table 1). The lack of correlation between the number of pests landing on their preferred colored nets, vs. the number penetrating through these nets, may suggest that the pests remain on these nets for an extended period of time (an arrestment response; Bukovinszky et al., 2005). Yellow shade nets were previously reported to affect aphids in a similar manner (Harpaz, 1982). The Red net did not differ from the black shade net, while the white and Pearl shade nets significantly lowered both aphid infestation and the incidence of PVY and CMV (Harpaz, 1982 and Table 1), probably due to their reflectivity of sunlight, deterring pest landing. Photoselective Insect-Proof Screens Reduce Thrips Infestation OptiNet® transmits only 40-50% of the UV range (280-380 nm) of solar radiation, compared with 80-90% by the standard transparent screen . At the range of 380-800 nm the OptiNet® transmits 60-70% of sunlight, compared with 85-95% by the standard screen. However, the reflection of sunlight in the range of 400-750 nm by OptiNet® was about 2.5 times greater than the reflection by the standard screen (not shown). The numbers of thrips (mainly Thrips tabaci) found on cucumber leaves in tunnels covered by the OptiNet® screen were significantly lower (3-9 folds), compared with the standard screen (Table 1). Similarly, fewer thrips were caught (about 5 folds) in tunnels of chive covered by OptiNet®, vs. the standard screen. The mechanism by which the OptiNet® provides better protection against arthropod pests may be explained by two alternative hypotheses: (i) the light inside the screen-house contains less UV and therefore becomes “invisible” to the pest (see Antignus and Ben-Yakir, 2004); (ii) higher levels of reflected/scattered sunlight deter pest landing (e.g. Matteson et al., 1992). CONCLUSIONS Photoselective, light-dispersive shade nets and screens provide a new tool that can be implemented within protected cultivation practices for improving crop performance, pest control and overall profitability of agricultural crops. The technology can be used by its own, in net- and screen-houses, or alternatively combined with other covering materials used in protected cultivation. ACKNOWLEDGEMENTS The studies of Shahak et al. in Israel were funded by the Chief Scientist of the Israeli Ministry of Agriculture and by the Israeli Plants Production and Marketing Board.

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Literature cited Antignus, Y. and Ben-Yakir, D. 2004. Ultraviolet-absorbing barriers, an efficient integrated pest management tool to protect greenhouses from insects and virus diseases. In: A.R. Horowitz, and I. Ishaaya (eds.). Insect Pest Management - Field and Protected Crops. Springer Publishers, Berlin, pp. 319-335. Ben-Yakir, D., Hadar, M.D., Offir, Y. Chen, M. and Tregerman, M. 2008. Protecting crops from pests using Optinet® screens and Chromatinet® shading nets. Acta Hort., in press. Bukovinszky, T., Potting, R.P.J., Clough, Y., Lenteren, J.C. van and Vet, L.E.M. 2005. The role of pre- and post-alighting detection mechanisms in the responses to patch size by specialist herbivores. Oikos 109:435-446. Harpaz, I. 1982. Nonpesticidal control of vector-borne viruses. Pathogens, Vectors, and Plant Dishases. Academic Press, pp. 1-21. Healey, K.D. Rickert, K.G. Hammer, G.L. and Bange, M.P. 1998. Radiation use efficiency increases when the diffuse component of incident radiation is enhanced under shade. Austr. J. Agric. Res. 49: 665-672. Matteson, N., Terry, I., Ascoli, C.A. and Gilbert, C. 1992. Spectral efficiency of the western flower thrips, Frankliniella occidentalis. J. Insect Physiol. 38:453-459. Nissim-Levi, A., Farkash, L., Hamburger, D., Ovadia, R., Forrer, I., Kagan, S. and OrenShamir, M., 2008. Light-scattering shade net increases branching and flowering in ornamental pot plants. J. Hort. Sci. Biotech. 83, 9-14. Oren-Shamir, M., Gussakovsky, E.E., Shpiegel, E., Nissim-Levi, A.,Ratner, K., Ovadia, R., Giller, Yu.E. and Shahak, Y 2001. Coloured shade nets can improve the yield and quality of green decorative branches of Pittosporum variegatum. J. Hort. Sci. Biotech. 76: 353-361. Oren-Shamir, M., Shahak, Y., Dori, I., Matan, E., Shlomo, E., Ovadia, R., Gussakovsky, E.E., Nissim-Levi, A., Ratner, K., Giller, Y., Gal, Z. and Ganelevin, R., 2003. Lisianthus: aumento di altezza di piante coltivate in estate sotto reti colorate. Flortecnica 6: 84-86 (in Italian). Rajapakse, N.C. and Shahak, Y. 2007. Light quality manipulation by horticulture industry. In: G. Whitelam and K. Halliday (eds.), Light and Plant Development, Blackwell Publishing, UK, pp 290-312. Shahak, Y., Gussakovsky, E.E., Gal, E. and Ganelevin, R. 2004a. ColorNets: Crop protection and light-quality manipulation in one technology. Acta Hort. 659: 143-151. Shahak, Y., Gussakovsky, E.E., Cohen, Y., Lurie, S., Stern, R., Kfir, S., Naor, A., Atzmon, I., Doron, I. and Greenblat-Avron, Y. 2004b. ColorNets: a new approach for light manipulation in fruit trees. Acta Hort. 636: 609-616. Shahak, Y., Ganelevin R., Gussakovsky, E.E., Oren-Shamir, M., Gal E., Díaz, M., Callejón, Á.J., Camacho, F. and Fernández-Rodriguez E.J. 2004c. Effects of the modification of light quality by photo-selective shade nets (ChromatiNet) on the physiology, yield and quality of crops. In: Proc. III Congreso de Horticultura Mediterránea, Expoagro’ 2004 pp. 117-137, (in Spanish). Shahak, Y., 2008. Photoselective netting for improved performance of horticultural crops. A review of ornamental and vegetable studies carried in Israel. Acta Hort., in press. Shahak, Y., Ratner, K., Giller, Y.E., Zur, N. Or, E., Gussakovsky, E.E., Stern, R., Sarig, P., Raban, E., Harcavi, E., Doron, I. and Greenblat-Avron, Y. 2008. Improving solar energy utilization, productivity and fruit quality in orchards and vineyards by photoselective netting. Acta Hort., in press.

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Tables Table 1. Summary of the effect of photoselective netting on pests’ invasion to, and establishment on, protected crops (arrows indicate the level relative to the reference). Covering type 50 mesh screens

Covering color White (UV block) White*

Reference covering

Whiteflies

Thrips

Aphids

Proposed mechanism

Transparent

2X-5X Ð

3X-10X Ð

2X-5X Ð

Reflection

No covering

NA

NA

40X Ð

Reflection

None

None

3X-4X Ð

Reflection

2X-3X Ð

None

2X-3X Ð

Arrestment

None

2X-3X Ð

None

Arrestment

None

None

None

NA

Pearl 18-35% Shade nets

Yellow Blue

Black

Red

*Data of Cohen reviewed by Harpaz, 1982. All other data refer to our current work. Figures Relative Transmittance of Total Light

Spectra of Scattered Light under Nets 2

A

Pearl

B

80

2 μE/m /s/nm

T, % of sunlight

90

black

70

Red Pearl

60

Yellow Red 1

no net black

Yellow 50 300

400

500 600 Wavelength, nm

700

0 300

800

400

500

600

700

800

Wavelength, nm

Fig.1. Spectra of transmittance of total (direct+scattered) light (A), and spectra of scattered light intensity under the colored nets (B). The transmittance spectra were derived from spectra of total light under each net divided by the spectrum with no net. Total and scattered PAR intensity was 1894 and 295 (no-net), 1379 and 482 (Pearl), 1382 and 221 (black) μmol/m2/s/nm, respectively, measured at mid, clear day on 06/07. 'Vergasa' fruit production rate

'Vergasa' cumulative yield 60000

A

0.4

40000 30000 20000 10000

Red Pearl Yellow Black

0

29.8.06

Fr/plant/day

Fruit/dunam

50000

B

Red Pearl Yellow Black

0.3 0.2 0.1 0.0

29.9.06 29.10.06 29.11.06 29.12.06 Harvesting date

0

20

40 60 80 100 Days of harvesting

120

140

Fig. 2. Cumulative fruit yield (A, number of fruits harvested per 0.1 Ha) and fruit production rate (B, # fruits/plant/day) in ‘Vergasa’ pepper under the colored Vs. black net during the 2006 season at the Besor experimental station.

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