Netting apple orchards, black or white net - what is the difference?

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What is the difference between black and white net? Is there a difference or is it just your preference. A netting demonstration at Lyster’s Orchard Manjimup, was set up to demonstrate the benefits of netting under Western Australian conditions.

Sensors installed in the orchard measured air temperature, solar radiation, relative humidity and fruit surface temperature and winter chill accumulation was calculated using the Dynamic model . Photosynthetically active radiation was measured using a hand held meter and phenology observations recorded.

Introduction

A netting demonstration site at Lyster’s Orchard, Manjimup, was set up to demonstrate the benefits of netting under Western Australian conditions.  Two sections of 16mm cross over quad netting were installed over an established Cripps Pink and Fuji orchard to assess their effect on protection from birds, sun and hail damage.  The demonstration established in November 2013 compared black net and white net to an area of non-netted (no net) trees within the same block in the orchard.

Specifications on the black net state a 23% reduction of both shade and UV radiation while white net stated a 20% reduction.  To test the effect of the netting, sensors were installed in each section to continuously measure mid canopy air temperature, solar radiation, relative humidity and fruit surface temperature.  A hand held meter was also used to measure photosynthetically active radiation during the season.

Winter chill accumulation and fruit quality were also measured together with observations of flowering to determine the dates of bud break, occurrence of first flower and full bloom.

Winter Chill

Winter chill was calculated from 1st March through until 31st August 2014 and 2015 from hourly temperature readings (Figure 1). There is no difference in chill accumulation under black net, white net or no net area.  The nets do not reduce the amount of chill accumulated as there is minimal impact on the temperatures recorded under the black or white net or no net.

Graph show data to support that there is minimal impact on the temperatures recorded under the black or white net or no net

Figure 1.  Chill accumulation under the black net, white net and no net in 2014 and 2015.

Flowering

Bud break and flowering data was collected from 10 trees under black, white and no net rows.  Observations were made three times a week from 30 August 2014 to 30 October 2014. Whole tree assessments were made to determine the dates of bud break, occurrence of first flower and full bloom and to monitor progression of flowering. There is minimal difference in flowering progression between the netted trees to the no net trees. All trees still came into full bloom at the same time in 2014.

Fruit growth rate

Fruit diameter was measured 6 weeks after full bloom until the first pick.  Little difference was measured in all sections during the majority of the season.  In March, apples under the black net measured 3mm larger on average than fruit under white net or no net. However, at harvest time there was no significant difference in diameter of fruit grown under any of the treatments.

Minor variability in irrigation, tree management and nutrition are likely to have greater impact on fruit size than netting.

Mid canopy air temperature

There was minimal difference between the black and white net for mid canopy air temperature and humidity.  Mean daily temperatures rarely varied more than 0.5 to 1 degree. The netting led to small increases in minimum temperatures and dampening of maximum temperatures. This action is similar to a cloud cover effect which reduces radiant heat loss overnight and reflects a portion of incoming daytime radiation reducing maximum temperatures.

Solar radiation and fruit surface temperature

The no net area received the highest solar radiation. While not exactly the same as the specifications, the white net showed a 15% reduction and the black net 26% reduction during January and February 2014 (Figure 2) and 2015.  Specifications are only given as a guide to how the nets will perform and in this case the black net was close to specification and the white net slightly less.

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Figure 2.  Solar radiation measured in the black net, white net and no net rows for summer 2014.

It is reasonable to assume that the amount of solar radiation reaching the fruit surface should influence the fruit surface temperature (FST). FST was measured over the summer 2013 and14 season (Figure 3).  Average FST was lower under the white net than the black net, even though greater solar radiation was recorded under the white net.

FST was significantly higher in the no net area, particularly during extreme heat events in late summer and a higher percentage of sunburnt fruit was observed.  There was no difference in sunburn between the black and white net areas, and both netted areas reduced sunburn significantly compared to the no net area.

Fruit surface temperature (FST) and air temperature measured in the black net, white net and no net rows for February till mid-March 2014.

Figure 3.  Fruit surface temperature (FST) and air temperature measured in the black net, white net and no net rows for February till mid-March 2014.

Photosynthetically active radiation (PAR)

The effective area of shade was calculated by measuring PAR on a clear sky day in February 2014 and 2015 using a hand held ceptometer. Several measurements were taken throughout each section at morning, solar noon and afternoon to measure the extent and density of the shade created by the tree.

While measurements reflected shade specification of the net, the reduction in PAR was also influenced by tree vigour. Figure 4 shows the black net had a greater reduction in shade compared with the white net and no net. Tree vigour was higher under the netted areas than outside the net.

Average fractional photosynthetic radiation interception (fPAR) measured at morning, noon and afternoon on 23 February 2015 in the black net, white net and no net rows.

Figure 4.  Average fractional photosynthetic radiation interception (fPAR) measured at morning, noon and afternoon on 23 February 2015 in the black net, white net and no net rows.

During the monitoring of the demonstration site low bird pressure years were experienced with no damage occurring outside or under the nets.

Netting has the capability of reducing bird damage and sunburn damage compared to the no net treatment.  No major hail event was experienced, but anecdotally netting reduces damage caused by hail as seen in previous studies in Queensland. The netting had no impact on the fruit growth rate, flowering was not affected and no significant differences were seen in winter chill between the no net, black net and white net.  The impact of the reduced PAR under the nets and the increased vigour could explain the poor colour development of the fruit.

 

 

Reference

Middleton S and McWaters A (2002). Hail Netting of Apple Orchards – Australian Experience.  The Compact Fruit Tree, volume 35, number 2, 2002

 

 

Contact information

Susan Murphy-White
+61 (0)8 9777 0151