Netting saves water at apple demonstration site

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Findings from the first year of an apple netting demonstration in Manjimup show that growing apples in a netted enclosure resulted in saving irrigation water. However it was clear that aspects of crop husbandry need to be fine-tuned in order to produce good commercial quality fruit.

Introduction

The first harvest of apples under a netted area at the Lysters’ orchard near Manjimup in April 2014 has shown mixed results. The site, netted in October 2013, aims to demonstrate the value of netting to improve water use efficiency and orchard productivity in high density production systems.

This DAFWA work is supported through funding from Royalties for Regions, the Department of Regional Development, Horticulture Australia and the Commonwealth Department of Agriculture, Fisheries and Forestry.

The 1.2 hectare (ha) demonstration site has 0.5ha of permanent net constructed over an established block of Cripps Pink and Fuji apple trees. Areas of black and white 16mm quad netting were installed, each covering 0.25ha. The remaining area contains two comparison blocks, a DAFWA-managed control, and a grower practice control.

Particular attention was given to assessing the impact of netting on fruit quality parameters such as sunburn, windburn, size, colour, firmness and sugars, while in-field data is being collected to compare tree development and chill accrual under the netting compared with outside.

There were positive results for water savings, prevention of sunburn and bird damage, but some challenges in management to obtain the required colour were identified. The first season resulted in good yields but low marketability of fruit throughout the block.

The coming season will see more attention in the timing of the use of colour accelerants and leaf and fruit analysis to guide crop nutrition and ensure a good quality  crop.

Fruit diameter and weight

A representatitve sample of 10 trees in each block was closely monitored. Five of the trees from each area were thinned and pruned by project staff (DAFWA-managed) and compared with the other five trees thinned and pruned by the grower (grower-managed).

Irrigation for both netted areas and the un-netted control area were managed by DAFWA staff using an independent irrigation system to allow for variation from the growers normal irrigation practice.

The average fruit numbers per tree for each treatment are shown in Table 1. Unintentionally, thinning and pruning practices were inconsistent among treatments within the demonstration and also differed from the grower's practice. Although there were differences in the fruit numbers per tree, this was not always reflected in fruit size and weight.

Table 1 Average number of fruit and percentage of non-damaged fruit per treatment

Average number of fruit per tree

Percentage of non-damaged fruit

Block

DAFWA-managed

Grower-managed

DAFWA-managed

Grower-managed

Black net

105

239

66.1

71.8

White net

150

197

77.9

77.6

Un-netted DAFWA

100

100

73.6

69.5

Un-netted grower

 -

200

55.0

Table 2 Average diameter and fruit weight at demonstration site

 

Block

Average fruit diameter (mm)

Average fruit weight (g)

DAFWA-managed

Grower-managed

DAFWA-managed

Grower-managed

Black net

72.3

70.9

168.6

162.9

White net

71.8

71.9

171.0

174.2

Un-netted DAFWA

70.4

72.5

167.3

176.7

Un-netted rower

-

67.6

-

140.8

The un-netted grower-managed area had the lowest fruit diameter and weight suggesting that netting and irrigation have an effect on these two factors (Table 2).

The aim next season will be to thin fruit to between 140 and 160 fruit per tree for all treatments in order to better match commercial practice and allow better treatment comparisons.

Irrigation and fruit quality and damage

Irrigation under the net and the DAFWA-run un-netted area was based on evaporation with soil moisture monitoring for fine-tuning. This was compared to current grower practice. Outside the net, the DAFWA-run area received 10% more water than the grower area (6.54 megalitres per hectare compared to 5.97ML/ha). The white net area received 5.53ML/ha and the black was the lowest with 5.16ML/ha applied.

The black and white net resulted in 15% and 7% lower water applications respectively compared with current grower practice but produced larger fruit. When compared with the DAFWA-run un-netted area, the reductions in water use were 22% and 16% respectively.

As expected, evaporation was reduced under both netted areas with the shade effect of the net resulting in reduced solar radiation which is a large driver of evaporation. Sensors under the black net measured 30% lower solar radiation compared with un-netted areas while sensors under the white net recorded an 18% reduction.

Fruit maturity and colour

Starch conversion, an indication of maturity, is measured on a scale from 1 (immature) to 6 (over mature and past the picking stage for controlled atmosphere storage). Apples at stage 2 are best suited to long-term storage, stages 3 to 4 medium term, and 5, short-term storage.

Starch conversion was between stage 3 and 4 throughout the demonstration block, while Brix, a measure of sugars, was generally lower than the expected minimum standard of 13%. This suggests that nutrition over the whole block needs some improvement to produce fruit of better quality.

Colour was assessed using the Centre technique interprofessionnel des fruits et legumes (Ctifl) Pink LadyTM Eurofru colour charts on 40 apples sampled from each tree.

Each apple was given a score for background colour (F1–F7) and blush intensity (R1–R8) and a percentage of blush intensity when the blush was over R3. For long-term storage and good taste quality, harvesting is recommended, on average, at the F3–F4 stage with an R4–R5 pink coloration.

As fruit is removed from storage, the background colour (F score) will increase leading to lower acceptance by the markets. While only 1% of fruit under the black net was above F4, 53% and 67% of fruit from the white net and the outside netted area were above (Table 4).

The biggest issue in this year’s demonstration was the lack of colour development. At picking, starch conversion scores were between 3 and 4, optimum for only short to medium controlled atmosphere storage. Table 4 shows that colour development was below the required R4 stage in 43% of fruit under black net. This was almost twice as much as fruit under white net (25%) and no net (26%).

Table 3 Background colour score from Ctifl standards for Pink Lady  (optimum for long-term storage F3–4)

Net

Background colour (F score)

<3

3‑4

>4

Black

6%

93%

1%

White

5%

42%

53%

None

2%

31%

67%

Table 4 Blush intensity, R score for pink colour from Ctifl standards for Pink Lady (optimum long-term storage R4-5)

Net

Blush intensity (R score)

<4

4‑5

>5

Black

43%

29%

28%

White

25%

38%

37%

None

26%

32%

42%

Fruit damage

Sunburn in the un-netted areas was up to 12.4%.  Sunburn under the netted area ranged from 0.2 to 0.4% of fruit harvested from the 10 trees in each treatment.

There was no bird or hail damage in the orchard this season so the benefit of the netting was not assessed for these factors.

Disease and insect pressure was higher under the netted sections. This is likely to be due to the increase in humidity and vigour of the trees. Woolly aphids were more abundant on the trees under net.

Conclusions

While reduced water requirements was demonstrated under netting, inconsistency in fruit numbers together with fruit colour and quality mean that quantifying these benefits needs further evaluation.

Greater attention to crop nutrition and management to ensure a quality marketable crop will be the priority for next season. Particular attention will be paid to maturity through earlier starch conversion tests with decisions on colour accelerants made with the Lysters when required, to achieve desired colour standards and storage condition.

Contact information

Rohan Prince
+61 (0)8 9368 3210
Susan Murphy-White
+61 (0)8 9777 0151