Making Sense Of Orchard Netting

Hein van Kralingen
Department of Primary Industries (DPI), Tatura Centre

Netting structures protect crops by placing a physical barrier between the crop, pests and the elements. There is a wide range of netting options available to growers, from temporary drape-over netting to permanent, full-canopy netting. Using the correct netting can offer protection from insects and birds, climate events such as hail, sunburn, windburn and fruit-rub due to wind, as well as having the potential to reduce water requirements. Further benefits may include a reduction in branch breaking, controlling beneficial insects inside full canopy structures, and preventing spray drift. Some negative components include the high capital cost and possibly the returns may not justify the investment. Plus permanent structures may be damaged by extreme weather events and the change in climate under netting may lead to crop loss if not managed correctly. “To net or not to net” is a publication available online from Queensland Department of Primary Industries and Fisheries that will assist growers make informed decisions about netting. The publication covers a variety of topics, including:

Figure 1. Permanent hail netting structure. 12 mm diamond mesh hail net is used in the above structures (see Fig 6)

1.	pests that can be controlled by netting and pest problems under nets	Figure 2. A typical netting structure (with permission, DPI Queensland, To Net or Not to Net)
2.	a description of full canopy netting and tunnel netting, types of netting materials and basic construction procedures
3.	the effects of changing microclimate under netting
4.	management strategies for effective pollination under netting
5.	alternative control methods for birds and flying foxes
6.	financial aspects of netting including cost of netting and a discussion of aspects that contribute to total costing and financial returns
7.	case studies (18) that describe different netting options; includes grower feedback
8.	a contact list for net manufacturers, suppliers and installation contractors in each state
9.	a list of referenced articles that supply more details on netting, climate, pest control and productivity for different crops under netting

For growers affected by hail, a new Horticulture Australia report investigates the use of hail netting in apple orchards. Hail remains a major threat to the production of quality pome and stone fruit in most growing districts in Victoria, with many international and local markets demanding top quality, blemish-free fruit. However, to date, the use of netting to prevent hail damage has not been readily adopted by Victorian fruit growers amid concerns of cost, tree growth and fruit quality.

Some findings of the report “AP 320: Hail netting to increase apple orchard productivity” include:

1.	hail netting reduces light (PAR) by up to 25 percent (self-shading could be more even without netting)	Fig 3. Black bird and bat diamond mesh net (15 mm) Fig 5.White bird and bat diamond mesh net (15 mm) Fig 7. Translucent monofilament fibre exclusion netting with light-weave (2 mm)	Fig 4. White bird and bat diamond mesh net (25mm) Fig 6. 12 mm diamond mesh hail net with quadruple cross stitch (5 mm) Fig 8. Translucent monofilament fibre exclusion netting with heavy weave (2mm)
2.	reductions in light beneath hail netting are significant, yet manageable
3.	Wind can be reduced by 50 percent or more whereas humidity may increase by up to 15 percent
4.	netting does not provide frost protection and has little effect on air, grass and soil temperatures. On warm to hot days, air and soil temperatures may be reduced by 1 to 3oC.
5.	apple tree response to hail netting is determined by vigour. Vigorous trees under netting show greater shoot growth and smaller fruit. In dwarf to semi-dwarf trees shoot growth shows no difference and fruit size is equal to or larger than on trees not under netting.
6.	tree vigour needs to be carefully controlled under netting. Mistakes in tree pruning are exacerbated under netting.
7.	netting affects pollination. Fruit set is reduced with fewer multiple clusters. Crop yield will be influenced by both pollination and tree vigour.
8.	fruit colour development in red varieties is determined by vigour and the position of fruits in the canopy.
9.	windrub and sunburn is noticeably reduced under netting.
Emphasis on pruning, crop load and thinning, irrigation scheduling and monitoring, and pollination and bee activity will need to be considered when contemplating netting. Producers should aim to control tree vigour, maintain good light distribution and maximise yields, fruit size and fruit quality through a range of management strategies.
		Figures 3-8. (with permission, DPI Queensland, To Net or Not to Net)

Orchard netting is an expensive investment. Yield of the crop under netting needs to be maximised while production costs and tree management costs need to be minimised. Yield is maximised by assuring the best possible light interception and fruit quality is improved by proper light distribution within the canopy. Early commercial yield, achieved through high density tree spacing and maintaining high levels of subsequent production, will assist in recouping the financial outlay of hail netting.

‘To net or not to net’ can be downloaded from the Queensland Department of Primary Industries and Fisheries website www.dpi.qld.gov.au (external site) or a hard copy can be obtained from Hein van Kralingen at DPI Tatura by calling (03) 5833-5311 or Email: hein.vankralingen@dpi.vic.gov.au.


For further information please refer to the following documents.

Additional literature
Goodman, R. and Middleton S.G. (1999). Honeybee pollination of crops grown under hail netting. RIRDC Information Bulletin and CD Rom.

Middleton, S.G. & McWaters A.D. (1996). Hail netting to increase apple orchard productivity, Department of Primary Industries and Fisheries, Queensland

Middleton, S.G. & McWaters, A.D. (2000). Maximising apple orchard productivity under hail netting, Department of Primary Industries and Fisheries, Queensland

Rigdon, P. (2008). To net or not to net – 3’rd edition, Department of Primary Industries and Fisheries, Queensland

Scott, B. (1989). The use of netting for hail protection – design and management considerations for pome fruit orchards. Acta Horticulturae 240, 147-150.