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A 'mitey' good approach to biocontrol

Cosmetic perfection is highly prized in many crops but in flowers it is considered essential. In cut flowers the tiny sap-sucking red spider mite (Tetranychus urticae) can cause serious damage and loss of value, resulting in regular spraying (up to 20 times each year) of insecticide. But the introduction of biological control using the spider mite's predator, Phytoseiulus persimilis, on the highly competitive rose-growing farms of Kenya has resulted in significant cost savings and improvements in leaf and bloom quality, as well as reducing the risk to the environment and workers from being exposed to pesticides.

The bio battle field

Red spider mite and phytoseiulus (Real IPM)
Red spider mite and phytoseiulus
Real IPM

The high-domed plastic houses of Enkasiti Rose Farm cover more than 28 hectares amongst the rolling hills of Thika, northeast of Nairobi. Eighteen varieties of roses, grown hydroponically in raised beds of cocoa peat, produce 48 million long-stemmed blooms a year, which are carefully checked and packed before being air-freighted to the Dutch flower auctions in Europe. "Our customers want beautiful tight buds but they also want glossy, dark green leaves with no damage," says production manager Mr Narayana, "which is why 70% of our pesticide use was against red spider mite. And with such intensive use of chemicals we were concerned about the development of resistance." However the spider mite has no defence against Phytoseiulus persimilis. Also a mite, its voracious appetite for spider mites has been proven in the glasshouse crops of Europe and North America. Such is the potential demand for it in Kenya that Phytoseiulus is now being bred in recently constructed bio-factories of biocontrol company Real IPM. The company's director, Louise Labuschagne guided Enkasiti farm through the early stages of switching to biological control.

"Traditionally, a grower could buy a bottle of insecticide from the local agrochemical supplier, read the instructions on it, apply the chemical and wait for the results," says Labuschagne. "Biological control is more complicated and requires new management skills and training - and support once the switch to biocontrol has taken place." Growers wanting to use biocontrol are always advised to start with a small area. In the case of Enkasiti, this initial trial went so well that it was decided that use of insecticides for mite control would cease.

Proving the potential

However, mites were endemic in the rose crop; it was estimated that there were in excess of 10 million in every hectare of roses. And with time needed for the predators to consume all these mites there were a nervous few weeks before control effects could be seen. "Frankly speaking, I was against biocontrol, especially when the numbers of red spider mite boomed," recalls Narayana, "but when the new shoots on the roses grew and I could see the declining damage from mites then I knew it was OK." His confidence grew such that over the next two years the use of the predators for spider mite control was adopted across the whole farm.

Crop scouting (Real IPM)
Crop scouting
Real IPM

Things now are better than OK. Overall rose growth has improved, as the plants are relieved of the stress effects from repeated insecticide use, and Enkasiti blooms have moved up a quality grade in the Dutch auctions. Their strong position in the market reflects the increasing concern over pesticide use among European buyers, which has led to tightening of regulatory standards for environmental protection and worker safety. Phytoseiulus are however, exempt from European phytosanitary penalties, so exporters such as Enkasiti show no anxiety over an occasional predator insect that might stow away on the cut flowers and be found by customs inspectors, although in over two years this has never occurred.

The future of biocontrol

Labuschagne believes that for many more farmers biological control of major pests will become a viable option, and not just under the cover of plastic or glass. "Traditionally biological control has been established in protected structures, but there is nothing to stop more biological control agents being used in field crops," she explains. "As long as the pest is present, the predator remains. Once the pest population is wiped out, the biological control agent will also disappear so there is no need to worry about creating an imbalance in the environment." Having conquered the spider mite at Enkasiti Roses, Narayana is now hopeful of biological control solutions for his other pest problems: aphids and mealy bugs. "For now we still have to use spot treatments with insecticides. But I would straightaway switch to bio-control for other insect problems too, if I could."

Date published: September 2005


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