Vineyards

Reprinted from THE AUSTRALIAN AND NEW ZEALAND GRAPEGROWER & WINEMAKER July 2002 No. 462

Fighting a good fight against birds in the vineyard

Marauding birds are among the most recalcitrant and frustrating hazards with which a grower has to contend.

After battling the many threats of disease and climate throughout the growing period, a great crop can be lost in one afternoon, just as you are about to reap the rewards for a year's hard work.

Two seasons ago Mark Bourne, of Highlands Vineyards, and Arthur King, of Oblomov Trading Co., set to work to find an economic and improved netting system. The result is a 'complete cover' method that is now used extensively throughout the Southern Highlands of NSW.

This area is one of the most recently declared wine regions and bird pressure there could easily be described as intense. Vineyards are surrounded by state parks, forests and virgin bushland, birds such as currawongs, native parrots, magpies, mynahs (Indian and noisy) and flocks of starlings are all permanent residents in the surrounding area. The district is a true cool climate with harvesting taking place from April to mid May each season and nets are required for up to 10 weeks. The cool climate region is starting to produce quality grapes commanding high prices from winemakers.

"You just can't take the risk of losing or damaging your crop due to birds in today's quality orientated marketplace," says Bourne. "It's not only the yield losses to consider, but also the potential damage to berries and the subsequent downgrading of fruit quality. There is also a temptation to harvest before the maturity levels are at a premium because of the risk of bird damage and loss." For many districts total exclusion is the only real answer to the production of quality grapes when there is increasing bird pressure.

Grumblebone Vineyard, Southern Highlands. Click to enlarge.

Watching costs

"You have to watch costs these days," he says. "It is not just the cost of purchasing netting that is important but the recurrent costs of application, maintenance and retrieval each season. We can get 30-gram two-ply net with 750mm reinforced edges for around $3600/ha plus $430/ha recurrent cost for application and retrieval. It's just good business sense. We can get around $18,000 a hectare gross off our better blocks, so if we save 12.5% loss to birds in any one year we have paid for half of the netting."

Many systems and nets were tried in the past. Single row nets were expensive to purchase and install. Nets draped down the sides of rows were stripped of grapes from birds eating grapes through the weave. Nets were pulled to the centre of rows and fixed under wires and pegs to alleviate this but labour costs, spraying access and install/retrieve times were excessively high. The only feasible solution was to lessen the area where birds can attempt a break-in - the edges.

Bourne covers his vineyards four or five rows at a time using 2-ply, 17-metre wide nets, with reinforced edges. They are erected using a "Net Wizz" application machine at a rate of up to a hectare an hour. The nets are joined overhead using the top foliage wire as a joiner so that the nets only go to the ground at the edges of the block.

Access for spraying is made easy by fitting cheap PVC or poly pipe, as ribs longways over the tractor and spray equipment (see attached photo). There is no reduction in spraying speeds or rates etc. Spraying can still be a one-man job, the driver just lifts the net at the ends of the rows, completes the sprays then drops the nets back down to the ground after the job is done.

A tractor and sprayer fitted with poly 'ribs' for negotiating the bird netting in a Southern Highlands vineyard, NSW. Click to enlarge.

"The net is laid over four rows and touches the ground at the base of the intermediate posts, the reinforced edge is then taken to the next row and placed over the top foliage wire and the wire is reattached to the posts or post clips," Bourn explained. "The same procedure is followed on the other side of the same row and the two foliage wires are married together using cheap cable ties, thus sealing the net over every fifth row. Using this method you do not waste netting going down the sides of rows to the ground but use it to cover an extra row. This cuts your purchase costs per hectare considerably and reduces the amount of labour required for application, maintenance and retrieval."

No need for cutting

It's a flexible net. On larger-scale vineyards or blocks, or when the bird pressure on the sides of nets is not so high, the same nets can be used to cover four rows and left to drape on the ground. No matter how you decide to arrange the net, there is no need to cut the net to suit your row length. Bourne uses standard 250m nets joined together. At the end of the row the net dropped to the ground and led to the start of the next set of rows making a continuous run throughout the vineyard. When one net finishes just overlap the next about a metre, join with cable ties and keep going, he says.

McVitty Grove Vineyard in the Southern Highlands of NSW. Click to enlarge.

Because nets are not cut to suit individual rows they can be moved from earlier to later varieties at different times of the year, if the situation suits. There is no fumbling for the right net or working out where those nets that have lost their row numbers belong, just grab the net at the front of the shed and start netting. Labour is a major component of costs in any vineyard. Efficient application, maintenance and retrieval of netting are an important factor, which should be considered when choosing a netting system. A wide net will cover more rows in one pass therefore taking less time to cover an area. The quoted cost of $430 a hectare for application and retrieval includes all labour (including on costs), cable ties, tractor fuel and maintenance costs.

On retrieval, the fact that the nets are joined and not cut to suit row lengths is a distinct advantage. The net is fed into the net machine at the start of the block and rolled up until the first join is reached. The machine is stopped, the cable ties/joiners quickly cut, the roll dropped then the new net is already in place for attachment to the new spindle. To newcomers to netting this may seem inconsequential but when you are retrieving hectares of nets a day the time saving in not rethreading nets through the top of net machines is considerable. Using 17m wide nets joined at each fifth post, as previously described, it is quite feasible to retrieve a minimum six hectares in an eight-hour day and in some situations 8-10 hectares.

HOW TO COMPARE NETTING

When choosing netting its important to compare like with like. A straight cost per square metre comparison might not get you the best long term deal.

1. The easiest way to compare value is to look at the weight per square metre and the cost per square metre keeping in mind that a two-ply net is about 25% stronger than a single ply of the same weight.

2. You should also ask about how the width of the net is calculated. When net is stretched along its length it loses width, and when it is stretched across its width it loses length. This means that ways of measuring width can be different from supplier to supplier.

3. Another important question is whether the UV treatment of the net is affected by common agricultural chemicals, such as sulphur and chlorine.