Armoured scales in floriculture
2016 – now
Transition from chemical to biological
More and more questions reach us from the floriculture sector. They would like to know whether, in addition to chemical intervention, a biological approach is also possible to combat pest insects. One of the reasons is the disappearance of chemical substances, forcing growers to look for biological alternatives. Armoured scales are one of the most difficult pests to control in the cultivation of Cymbidium. Until now, this has been done almost exclusively chemically and often several times a year intervention is necessary to prevent the plants from being ‘run over’. With the help of two Cymbidium growers, we have found a way to successfully combat armoured scales in floriculture.
First experiments with biolgical control agents
In 2016 we were asked about the options to biologically control armoured scales in Cymbidium. We have started a trial with the use of natural enemies at two growers, Bac Orchids and Ben van der Kooij Orchids. The aim was to investigate in practice which control agents are most suitable. We saw that there were two species of armoured scales on Cymbidium at one of the growers: boisduval scale (Diaspis boisduvalli) and oleander scale (Aspidiotis nerii). We have therefore released natural enemies specialized against armoured scales at both locations: the predatory beetles LINDIX and CHILIX and the parasitoids SCALEX-Ec and SCALEX-Am. We started with a biweekly introduction of natural enemies in which five repetitions were applied.
Establishment of predatory beetles and parasitoids
After the third introduction, there was little evidence that any of the released natural enemies were established. However, we did find feeding traces of the released LINDIX beetles. It was only after the fourth introduction, about seven weeks after the first introduction, that there was evidence of settlement and that we found a lot of larvae and beetles. We also saw the establishment of released parasitoids on the oleander scale at both growers. SCALEX-Ec in particular was well established on the oleander scale and to a lesser extent we also found SCALEX-Am.
KARNYOTHRIPS as addition
In addition to the beetles LINDIX and CHILIX and the parasitoids SCALEX-Ec and SCALEX-Am, the predatory trips KARNYOTHRIPS has also been released. This predatory thrips is not specialized in cleaning up armoured scales, but it settles at the base of the plant and feeds there on all kinds of insects and mites. In the case of Cymbidium they crawl between the bulbs, where we regularly find them behind the bracts of the bulbs. Hot spots of armoured scales usually occur in this part of the plant. While these narrow spaces are not easily accessible for beetles, KARNYOTHRIPS can access them.
The results of 2017 were promising and in 2018 Dico Bac (Bac Orchids) decided to fully implement biological control at his company to get the armoured scales under control.
From mid-February onwards, we released LINDIX, KARNYOTHRIPS and both parasitoid species on a weekly basis. In the summer of 2018 it was very hot for a long time. Then LINDIX’s efficiency decreased somewhat. It turned out that, at temperatures of 35 degrees or higher, this predatory beetle is no longer very active. This caused the armoured scales to reappear, but after the warm period LINDIX picked up the control again and the armoured scales decreased in numbers. This shows that LINDIX performs especially well in the cooler months.
Transition to organic cultivation
In 2019, LINDIX proved to be well established and further introduction was no longer necessary. Chemical intervention was no longer necessary to combat the armoured scales. At the company of Gertjan Bac (Bac Orchids), where until then mainly chemical intervention was used to control armoured scale, it was decided at the end of 2019 to also start growing organically. By exchanging plants with his brother Dico, it turned out that there was already a population of LINDIX and parasitoids, so we did not have to put out much extra to get the armoured scale infestation under control.
Biological control armoured scale succesful
This example clearly shows that even difficult pests such as armoured scale can be well controlled with biological control. Dico and Gertjan Bac are very satisfied with the transition to biological control and do not want to go back to the old approach.