SATI Beyond The Bunch 2nd Quarter 2024

The two plastic systems Plastic covers fall into two broad categories: temporary and fixed. Temporary covers are plastic strips that rest directly on the vine canopies. Fixed covers are elevated above the vines on permanent support structures

similar to those used for protective nets. The two systems are compared in Table 1.

Table 1 The characteristics of different plastic cover systems summarised.

Temporary

Fixed

Support

Rests on vine canopy.

Post and wire structures.

Lifespan

Usually one year.

Plastic: 3–10 years. Structure: permanent.

Labour

Intensive to deploy and remove plastic.

Intensive to install structure. Less so to deploy and remove plastic.

Relative cost

Lower.

Higher.

Main risk

Excessive humidity and condensation.

Structural failure.

must compare plastics with similar radiometric and other properties when evaluating quotes. Labour and materials for support structures add to the cost of fixed covers – expect to pay at least as much and perhaps more than for shade-netting support structures. Saving on support structures will lead to, at best, sleepless nights and, at worst, collapsed covers. The plastic sheets of fixed covers last longer than temporary ones but must nonetheless be replaced regularly. Plastic lifespan is usually inversely related to price. Vine damage should be minimal with temporary covers or early deployment of fixed covers. Working with fixed covers later in the season becomes more challenging as the canopy expands. Northern Cape growers report problematical high humidity and condensation under temporary plastic strips. Western Cape growers could have better results, especially if they have drip rather than microsprinkler irrigation.

Temporary plastic strips are commonly used for rain protection. They can theoretically be rolled out quickly when needed, although this still requires sufficient labour to get the job done before it rains. In established vineyards, growers do not need to modify existing trellises for temporary plastic strips. Well-secured strips may be less prone to wind damage than elevated plastic covers. Fixed plastic covers are attached to permanent support structures that elevate them 50–100 centimetres above the canopy. Growers unfurl the plastic to cover their vines at some point before or during the season. They roll it up and store it attached to the supports after harvest. Support structures are best erected when new vineyards are established, but existing trellises can be modified for fixed covers. Plastic costs are a significant component of system costs and vary enormously depending on supplier and characteristics. This is another reason why growers

Nets and caps

However, fixed plastic covers are a possible substitute for nets when the primary goal is creating a softer growing environment. Some growers successfully protect their crops from rain by capping bunches individually, and caps may be a good alternative to temporary plastic strips for specific situations.

The interaction of protective netting and plastic covers depends on the grower’s aims. If fixed plastic covers and netting are too close together, they can restrict air circulation. Temporary covers are probably a better option under nets. Plastic covers will lessen the impact of hail but are not a replacement for hail nets in high-risk regions.

BEYOND THE BUNCH • 7 • KWARTAAL 2 • 2024