Disease & insect control in grapes

The Rossouws of Mooigezicht Estates in De Doorns in the Cape Winelands have made the science of table grape production more precise than ever. Each hectare of the 300ha produces around 50 000 bunches of grapes.

“Our priority is to produce table grapes of outstanding quality and to secure maximum yields in a sustainable way,” says Francois Rossouw.

To achieve this, they follow a comprehensive integrated pest management system that includes vineyard monitoring, using agrochemicals responsibly and implementing biocontrol strategies.

The Hex River Valley experiences high disease pressure due to environmental conditions that favour the development of various diseases.

Rain in early spring usually leads to phomopsis on the newly developed leaves, while regular showers until the end of spring create optimal conditions for downy mildew. In summer, higher temperatures with lower rainfall encourage the development of powdery mildew. These fungal diseases can rapidly escalate to epidemic proportions and have caused significant crop losses in the past.

It is thus critical to use the best chemicals to protect the crop and reduce the risk of crop losses, says Francois.

To control the spread of fungal diseases, the family follows a preventative spraying programme designed by crop and weed protection company, Viking Marketing.

“The chemicals must be applied at the optimal time to suppress disease development. But we must also comply with the minimum residue levels permitted by global markets,” says Francois.

Their integrated pest management programme includes using weevil barriers and sterile insect technique (SIT) to control fruit fly.

In SIT, sterile fruit flies are released to mate with naturally occurring fruit flies, and this reduces the number of offspring generated.

This strategy is integrated with fruit fly spraying to keep the fruit fly population as small as possible.

Weevil barriers limit the movement of weevils from inside the soil up to the surface. “Applying the weevil barriers is very labour-intensive but it helps us to limit chemical use, while still effectively controlling weevil infestation,” explains Francois.

Specially trained personnel monitor the vineyards every second week to detect potential outbreaks of fungal infections or early insect infestation.

Mooigezicht uses electrostatic sprayers imported from the US to apply agrochemicals more effectively. Air-assisted electrostatic sprayers spray droplets that are 900 times smaller than those produced by conventional sprayers. These are carried deep into the plant canopy in a high-speed airstream.

“These sprayers make it possible to achieve better results while using less chemicals and less water,” says Francois.