“I’ve been using biological control since quite some time, but for aphids I thought I needed chemicals,” says Christiaan. “Until two years ago we sprayed against aphids once every two weeks on average, but over time the aphids seemed to rebound faster and faster. Among the chemicals that are currently authorized there is none that maintains a good efficacy against aphids.”
“I did try to use biocontrol against aphids in past, releasing from time to time parasitoid wasps (Aphidius) to deal with aphid hot spots. That worked well, but the problem in roses is that the mummies were visible on the stems at harvest. In ornamentals, we’re looking to deliver a spotless product. Even if these mummies are fully natural, this is perceived as a quality issue.”
Biobest Netherlands advisor Marcel Verbeek suggested Christiaan to set up a trial with the gall midge Aphidoletes instead of using parasitoid wasps. This gall midge is a full-blooded predator and hence leaves no mummies on the stems.
The trial was a big success. The gall midge did an excellent job. Marcel Verbeek: “Using the right natural enemy is only part of the trick. It’s equally important to provide it with the right environmental conditions to succeed. In the case of Aphidoletes, a suitable environment for mating is essential.”
Christiaan did the trick with buckets with humid coconut substrate on the bottom covered by some old newspaper. That, in fact, mimics the conditions in nature which are suitable for mating of the adult midges. From there on they’ll venture happily into the greenhouse looking for aphid hot spots.
Aphidoletes is well known to have an excellent searching behaviour. With only 20 buckets, Christiaan achieved excellent aphid control on 4 ha of roses. “That’s only about 0,2 individuals per square meter, which looks like not a lot at all but it was enough to achieve a great result.”
With Aphidoletes against aphids Arend Roses adds a new, highly effective biocontrol agent to its biocontrol mix. Christiaan: “Having achieved good biological control of whitefly, spider mite and thrips, we are now also on top of the aphid problem with a natural solution. We really found the missing link for a total biological systems approach.”