Willem Slootweg reached his limit in 2010: chemical agents were no longer working against the huge whitefly infestation in his Veronica crop. With the help of Koppert South Africa, he managed to get the problem under control in just a single summer. Since then, Slootweg has been using beneficials and integrated pest management more and more.

At the Semperflora company near Bokfontein, just outside of Pretoria in South Africa, Willem Slootweg and Cees Vooys grow twenty different varieties of summer flowers. Their most important crops are Annual Gypsophila, fountaingrass, Limonium (including statice), and Lisianthus flowers. They also produce seasonal crops which are sold in the summer or winter. The majority of the production is intended for the domestic market. The company has 100 employees, and cultivation takes place under plastic hoop houses with open sides.

Sometimes severe infestations

In the area around Pretoria, the summers, which last from October to March, can be mercilessly hot. It’s perfectly normal for the temperature to stay above 35°C for eight to ten weeks at a time. This can result in severe pest infestations. Whitefly is one example of this. Willem Slootweg was plagued by whitefly in his Veronicas for more than ten years. The effect of chemical agents was getting weaker every year until ultimately they stopped working altogether. Willem contacted Frank Enthoven of Koppert South Africa and asked if Koppert had a biological solution for a problem that had become uncontrollable. ‘We did have to experiment a bit,’ he says. ‘But we soon hit on a combination of Swirski-Mite (Amblyseius swirskii) and Verticillium lecanii. These two products solved the problem incredibly quickly. My crop was saved in just a single summer.’ Slootweg also uses yellow Horiver sticky traps to catch large numbers of whitefly.

More and more biological solutions

Since then, Semperflora has been using biological crop protection more and more. Willem Slootweg says that he now uses natural enemies on three of his nine hectares. For instance, he uses Miglyphus (the parasitic wasp Diglyphus isaea) against leaf miners in his Annual Gypsophila. This approach shows outstanding results: ‘The leaf miners are completely resistant to chemical agents. But now I can market Annual Gypsophila without any visible damage. That certainly wasn’t the case before.’ Once in a great while, Slootweg will use corrective methods, such as in the winter, when Miglyphus can’t entirely keep up with the leaf miner. But in those cases he also immediately deploys extra parasitic wasps. ‘The population then quickly increases. The problem never gets out of hand.’ Since last year, he’s also been using biological methods to combat spider mites in his Annual Gypsophila. Chemical agents had stopped working on spider mites, too. The company learned a valuable lesson last year, when chemical residue got inthe way of the biological methods. ‘Around here, spider mite populations can explode in a matter of days. Because of the residue, it was difficult for a while. But we carried on, and Spidex (Phytoseiulus persimilis) got the pests under control.’ In 2013, Willem has been working with Frank Enthoven and Erik van Santen, a consultant at Koppert Netherlands, using Spical (Neoseiulus californicus) preventatively as well as deploying Spidex as necessary. As of late September, it appears that this approach is a success.

A stronger plant

Powdery mildew and downy mildew can be a problem in Limonium. Here Willem Slootweg tests a completely natural product which disrupts the metabolic process in fungi and bacteria, and a biostimulant which strengthens plant vitality while leaving natural enemies unharmed. Semperflora also uses the beneficial fungus Trichoderma harzianum. It is currently being tested on a monthly basis in the outdoor cultivation of Delphinium. Willem wants to achieve optimum growth in this six-month crop.

The grower also tests Trichoderma to Lisianthus flowers before planting. In this way he hopesto achieve a stronger plant which has greater resistance to soil-borne diseases. In late 2013, he will also be using the complete NatuGro package on this crop. Willem says, ‘Initially it will just be a trial. But because Lisianthus is difficult to cultivate, yet offers potentially high returns, I want to reduce losses. I think that NatuGro can help with this.’

Equal costs and fewer worries

The grower is relying more and more on biological crop protection. He meets regularly with Frank Enthoven and Erik van Santen. ‘We share the same vision,’ Willem says. ‘If you want biological crop protection to be a success, you should never use it halfway, but make use of all options and give them a chance to work. That’s the key to success.’

Have his costs increased? ‘My costs for using biological methods are equal to the cost of chemical methods. In Annual Gypsophila, I originally had to introduce a great many beneficials. But once the population established itself, I didn’t need any new beneficials for a long time. That works out to the same costs.’

In conclusion, Willem says, ‘What’s at least as important is the fact that I have much fewer worries these days. Things are going well and I’ve never regretted switching over to biological methods. I’m a satisfied customer.’

For more information:
Koppert Biological Systems
Tel. +31 (0)10 5140466
Fax +31 (0)10 5115203

Source: BioJournal by Koppert Biological Systems