Netting saves water at apple demonstration site

Page last updated: Friday, 23 August 2019 - 4:21pm

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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