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Acta Hortic. 1268. ISHS 2020. DOI 10.17660/ActaHortic.2020.1268.39
Proc. XI Int. Symp. on Protected Cultivation in Mild Winter Climates and
I Int. Symp. on Nettings and Screens in Horticulture
Eds.: J.A. Fernández et al.
293
Assessment of a netting system for apple production in
a Mediterranean semi-arid climate
A.M. Aoun
Faculty of Agriculture and Food Sciences, American University of Beirut, Lebanon.
Abstract
Photoselective nets were used for protected apple cultivation system in a semi-
arid Mediterranean climate in Lebanon. For two seasons, blocks of trees from early
bearing and late bearing cultivars were covered with nets in an experimental orchard
and compared to uncovered blocks of trees in the same orchard. Microclimate data
were monitored throughout the seasons and pests scouting was performed weekly in
both treatments. The assessment of the protective netting system covered its impact on
tree physiology and production indicators, postharvest fruit quality indicators,
microclimate modification and its ability to exclude major insect pests without the use
of insecticides. Two years data collection and analysis seems to indicate that the netting
system is a promising tool for a better quality fruit in both cultivars and an overall tree
health with the opportunity of significantly reducing the need for pesticides.
Keywords: tree fruit production, nets, photoselective, apples, postharvest quality, light stress,
codling moth
INTRODUCTION
Netting is being tested around the word in tree fruit production as an efficient way to
protect crops against climate challenges i.e., excessive radiation (light and heat), hail, wind,
and against biological challenges i.e., flying pests (insects, bats, birds) and to improve quality
and yield (Manja and Aoun, 2019). For a recent exhaustive review on the use of nets for tree
fruit crops and their impact on the production refer to Manja and Aoun (2019). Thanks to
technological advances with photo-selective plastic filters, colored nets have been developed,
which provide differential filtration of solar radiation together with physical protection. In
plants, including some fruit trees, it has been demonstrated that changes in light composition
in red, far-red and blue spectra affects significantly fruit tree plant responses and could be a
useful tool for sustainable (e.g., lower use of chemicals and labor-practices) management of
yield and quality in modern orchards (Bastı́as and Grappadelli, 2012). However, the potential
use and benefit of this technology in fruit tree production remain under-explored and needs
to be optimized depending on the species/cultivar and geographical region.
The aim of this study was to assess the use of red photoselective nets with 20% shading
factor and a mesh size of 5.2×2.1 mm in a full block incomplete exclusion system with nets
covering entire plots without excluding the soil from the trees under semi-arid Mediterranean
climate. A detailed report on the first year experiment is published in a previous article (Aoun
and Manja, 2018).
MATERIALS AND METHODS
Trial design and net specifications
The experiment was conducted in a research apple orchard at the American University
of Beirut/Advancing Research Enabling Communities (AREC) Center in Lebanon. The apples
were planted in 1999 at 4.5×3.5 m spacing. The experiment included two treatments: covered
and uncovered trees from ‘Jonagold’ (early cultivar) and ‘Fuji’ (late cultivar). Six trees per
cultivar were followed for each treatment for a total of 24 trees. The covered trees were
randomly dispersed in four blocks with two or four trees per block of both cultivars. The
photoselective red nets (N Leno 3640(red) Polysack, Green.tek, Inc., Janesville, WI, USA) with
294
a 20% shading factor and a mesh size of 5.2×2.1 mm were installed at fruit set in 2017 (May
10) and after petal fall in 2018 (April 18) in a full block incomplete exclusion system and were
pulled back at ‘Fuji’ harvest end of September.
Parameter measurements
Temperature and humidity were measured using sensors (HOBO Pro V2 data logger,
Onset, USA) during the whole season. Light intensity was measured using sensors (HOBO
Pendant data logger, Onset, USA). Photosynthetically active radiation was determined using a
portable light meter (LI-189, LI-COR, USA) at mid-canopy layer.
Measurements of vegetative and reproductive growth were taken in July of both years:
the average length of five annual shoots and five clusters per tree respectively were
determined. Chlorophyll fluorescent parameters were also assessed using a portable
fluorometer (model OS-30p, Opti-Sciences, Hudson, New Hampshire, USA).
Diseases incidence and pests’ presence and damage on leaves were assessed once a
week on 15 annual shoots per treatment per cultivar. Pests’ damages on fruit were also
assessed weekly on 15 fruits per tree per cultivar. Traps were set in each treatment to scout
codling moth and fruit flies adults.
Fruit harvest was performed on August 29, 2017 and August 20, 2018 for ‘Jonagold’
trees; and on October 3, 2017 and September 27, 2018 for ‘Fuji’. A total of 120 apples per
treatment per cultivar were harvested in order to evaluate the apples physicochemical
characteristics. The weight and size of each apple were measured using an analytical balance
(AB-204 S, Mettler Toledo, Switzerland) and a caliper respectively. The percentage of the red
blush surface of the apple skin was assessed subjectively. Apples were sorted based on the
size and impurities on the skin according to national standards for apples Libnor, No.477,
2001. Sixty apples per treatment per cultivar were subjected to further assessment. Flesh
firmness was measured with fruit pressure tester fixed on a stand and fitted with an 11.3-mm
diameter head (mod. FT 327 (3-27lbs), Italy). Solid soluble content was estimated using a
digital hand-held pocket refractometer (PAL, Atago Co, Japan). Starch index was determined
by performing the starch iodine test and assessed based on Cornell University Chart. The
apple titratable acidity was determined using an auto-titrator comprising pH Module 867
(Metrohm, Switzerland).
Statistics
Statistical analysis of the data was performed using SPPS version 24 (IBM corp, Armonk,
IL, USA). Shapiro-Wilk test was used to assess the data for normal distribution and Levene’s
test was used for homogeneity of variances. When the assumptions for normality were not
respected, transformations were first applied. If no transformation assumed normality, non-
parametric tests were performed including chi-square and Man-Whitney test.
RESULTS AND DISCUSSION
Microclimate and annual growth measurements
Netting reduced PAR radiation by an average of 23% compared to open-field conditions.
This result corresponded with the shading factor of the nets used in the experiment (i.e.,
20%). The net significantly reduced photosynthetic photon flux density compared to control
with the highest difference recorded at 12 pm This shading caused by nets positively affected
photochemical efficiency of PSII in leaves as Fv/Fm ratio was significantly higher in leaves of
netted trees (0.8±0.001 in both seasons) compared to uncovered control trees (0.78±0.001 in
both seasons). According to Retamales et al. (2008), in countries with high levels of radiation,
shading nets may decrease stressful conditions during midday hours and protect crops from
extreme light levels, avoiding heat stress and photosynthesis inhibition. No differences were
recorded in terms of temperature and relative humidity between treatments in both seasons
nor between fruit set or annual vegetative growth.
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Biotic and abiotic stresses
Powdery mildew (Podosphaera leucotricha) was the only observable disease that
infected the orchard during May and June of both seasons, but no significant differences were
recorded between treatments yet ‘Jonagold’ was more affected than ‘Fuji’. Also, mites
(Tetranychus urticae), leafminers (Phyllonorycter spp.), rosy aphids (Dysaphis plantaginea),
green aphids (Aphis pomi) and woolly aphids (Eriosoma lanigerum) were rarely observed in
the orchard. However, nets offered satisfactory protection against codling moth (Cydia
pomonella) in both cultivars and in both seasons (Tab le 1). In addition, the season cumulative
of codling moth adults caught in traps was 3 times higher in the control treatment compared
to net during both seasons. Male moths flying between rows and on top of the trees, which is
the main location for female calling and prospecting prior to mating; seem to be efficiently
excluded by the nets (Sauphanor et al., 2012). Male fruit fly (Ceratitis capitata) population
caught in yellow trap containing an attract and kill pheromone gel was found 3.5 and 2.5
higher in control compared to net in 2017 and 2018, respectively. However, no fruit flies’
damages were observed on fruits. Sunburn and bird fruit damage were observed occasionally
in the control on ‘Fuji’ apples at harvest but not found under nets (Ta b le 2). This suggests a
potential for the net to protect against these damages.
Tabl e 1. Number of observed damages on ‘Jonagold’ and ‘Fuji’ apples attacked by codling
moth throughout the season.
Treatmenta
Jonagoldb
Fujic
2017
2018
2017
2018
Control
20
24
54
24
Net
8
8
9
1
aDifferences are significant between treatment in both years for each cultivar.
bn = 165 observations.
cn = 210 observations in 2017 and 240 observations in 2018.
Tabl e 2. Sunburn and bird damage found on ‘Fuji’ apples at harvest.
Treatment Total apples
Sunburn
Bird damage
Count
(%)
Count
(%)
2017
2018
2017
2018
2017
2017
Control
120
14
23
12
19
5
4.17
Net
120
1
0
0.8
0
0
0
Fruit quality assessment
Nets had a significant positive effect on most of the postharvest quality parameters
assessed in this study especially fruit weight, size, and color blush percentage (Tables 3 and
4). This may be the result of less stressful climatic conditions under nets as shown by the
chlorophyll fluorescence measurements. These results translate well in the grading of the
apples according to commercial official standards.
Apples grown under nets were usually slightly softer under nets (Tables 3 and 4);
However, no significant differences were recorded for soluble sugar content and malic acid.
Tabl e 3. Quality assessment of ‘Jonagold’ apples.
Treatment
Weight (g)
Size (mm)
Red blush (%)
Firmness (lb)
2017
2018
2017
2018
2017
2018
2017
2018
Controla
133a
132a
67a
67a
24a
59a
10.2a
10.4a
Netb
141b
139a
68b
67a
34b
64b
9.5b
9.5a
aMean values. Different letters represent significant differences between treatments per year for each parameter at P<0.05
bn = 120 apples per treatment except for firmness, n = 60.
296
Tabl e 4. Quality assessment of ‘Fuji’ apples.
Treatment
Weight (g)
Size (mm)
Red blush (%)
Firmness (lb)
2017
2018
2017
2018
2017
2018
2017
2018
Controla
125a
97a
66a
60a
32a
50a
11a
11.2a
Netb
135b
117b
68b
64b
43b
40b
10b
10.7b
aMean values. Different letters represent significant differences between treatments per year for each parameter at P<0.05
bn = 120 apples per treatment except for firmness, n = 60.
CONCLUSIONS
The shading caused by nets in a semi-arid climate positively affected the photochemical
efficiency of photosystem II. In addition, nets significantly protected against codling moth
while improving postharvest quality. Apples under net were better graded than apples in
control. Hence the need to evaluate the economic feasibility of nets in intensive orchards and
to collaborate with the industry to develop locally produced and adapted netting systems.
ACKOWLEDGEMENTS
This project was funded by a seed grant from the faculty of agricultural and food
sciences at the American university of Beirut.
Literature cited
Aoun, M., and Manja, K. (2018). Impact of the use of photoselective nets on two apple cultivars in a Mediterranean
orchard. Paper presented at: II International Symposium on Organic Horticulture for Wellbeing of the Environment
and Population, XXX International Horticultural Congress, IHC2018 (Istanbul, turkey: ISHS).
Bastı́as, R.M., and Grappadelli, L. (2012). Light quality management in fruit orchards: physiological and
technological aspects. Chil. J. Agric. Res. 72 (4), 574–581 https://doi .org/10.4067/S0718-58392012000400018.
Manja, K., a nd Aoun, M. (2019). The use of nets for tree fruit crops and their impact on the production: a review.
Sci. Hortic. (Amsterdam) 246, 110–122 https://doi .org/10.1016/j.scienta.2018.10.050.
Retamales, J., Montecino, J., Lobos, G., and Rojas, L. (2008). Colored shading nets increase yields and profitability of
highbush blueberries. Acta Hortic. 770, 193–197 https:/ /doi.org/10.17660/ActaHortic.2008.770.22.
Sauphanor, B., Severac, G., Maugin, S., Toub o n, J . F. , and Capowiez, Y. (2012). Exclusion netting may alter
reproduction of the codling moth (Cydia pomonella) and prevent associated fruit damage to apple orchards.
Entomol. Exp. Appl. 145 (2), 134–142 https://doi.org/10.1111/j.1570-7458.2012.01320.x.