‘Before the problem starts, build up a vigorous predator population’

Food supplements for predatory mites in vegetables
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‘Before the problem starts, build up a vigorous predator population’

Supplementary feeding of predatory mites with a pollen preparation has outgrown the trial phase. A large number of growers is successfully using this method. While pest numbers are low, predators that also eat pollen have the chance to build up a vigorous population. Dutch growers Wesley Klauwi from sweet pepper nursery Zuidgeest Growers and cucumber grower Bart de Groot explain how they do it.

“Snack peppers are different from standard pepper varieties, and you have to learn to respond to that.” Wesley Klauwi is responsible for crop protection at Zuidgeest Growers, a nursery famous for its Vitapep orange snack pepper. “Caterpillars and aphids are the biggest problem at this nursery. We have the other pests well under control, even though we have had a lot of pressure from thrips here over the last couple of years”, he explains.
The sweet pepper nursery gained experience this year with supplementary feeding of predatory mites with Nutrimite, a preparation based on cattail pollen. It is highly nutritious for predatory mites and unattractive to pests. What’s more, this pollen doesn’t produce allergic reactions.

Spreading pollen

In the first week of January, Amblyseius cucumeris was used to control thrips on the four hectare site in Maasdijk (south-west Netherlands). A bag was hung on every twelfth plant, and Amblyseius degenerans was added two weeks later. The rows in the greenhouse are 50 metres long. Klauwi opened the tubes halfway down the rows. He then provided three to four batches of supplementary pollen at 14-day intervals.
He disperses the product with a small leaf blower, first around the places where he has distributed the A. degenerans and then around the whole greenhouse. “We want to see plenty of predatory mites round about March, and we have achieved that at all our sites,” he says.

Good results

Supplementary feeding of natural predators is becoming more and more popular. Marcel Verbeek of Biobest says that about half of his customers now feed pollen. The major advantage of this method is that it allows natural predators to develop well at a time when there are not yet enough pests to sustain them. Predatory mites in a sweet pepper crop can often survive simply on the pollen from the flowers, but a cucumber crop produces no pollen at all. This makes it much harder to build up a good population of natural predators.
Several predatory mites eat the pollen preparation, namely A. degenerans, A. swirskii and Eurseius gallicus. A. cucumeris also responds to the preparation but less vigorously than swirskii and degenerans. “We are seeing good results. Proponents are finding that it makes the predatory mites more active and more vital. Others believe that the mites can get lazy or that they would prefer to eat pollen than catch pests.” Verbeek doesn’t agree.
Sometimes it is hard to make a sound choice. The advice is to disperse a total of 0.5 kg per ha each time. Supplementary feeding is not cheap but it delivers good returns because of the increased numbers of predatory mites in the crop.

Resilient population

“We are certainly seeing plenty of Amblyseius degenerans running around on the flowers,” says Klauwi. “Thrips are under control and this predatory mite also tackles spider mite. We hope that Orius will help with pest control in around week 25.” They prefer the combination of A. cucumeris, A. degenerans and supplementary feeding with pollen. “As far as we’re concerned, supplementary feeding is the future.”
Verbeek: “Our advice is to build a resilient population of natural predators before problems start arising in the crop. Sometimes this even starts with the breeder. Some growers are already releasing predatory mites at the propagation stage as well as providing supplementary feeding with the preparation.”

Gradual start keeps down costs

“Supplementary feeding doesn’t come cheap,” says Bart de Groot, Aad and Ruud Zwinkels’ partner from Kwintsheul in the Westland area. They have been using the pollen preparation at the 28,000 m2 cucumber nursery for a couple of years now.
The cucumber growers plant three times a year. To begin with they release A. swirskii at a rate of one bag per four plants to control thrips and whitefly. When the first spider mite appears, they add Phytoseiulus. Although the preparation is very effective for the predatory mite population, they decided last year to take a more gradual approach to keep costs down. In April 2015 the pressure from whitefly increased and there were not enough swirskii present to tackle the problem, so they decided to start supplementary feeding again.
This year, the course of events is the same as in 2014. De Groot is using 0.25 kg pollen per hectare per week on this fast growing crop. “But we still notice that this is saving us a round of predatory mites,” he explains. “Incidentally, we don’t have a lot of trouble from thrips. It’s mostly whitefly that we need to keep under control.”

Fan is faster

The leaf blower they used for dispersing the preparation in the first two years has now been replaced by a fan on the pipe rail trolley as dispersing the pollen with the leaf blower took too long. The grower can now get the job done in 45 minutes. He does it early in the morning before the vents are opened. He positions the trolley so that the fan is about half a metre above the wire. Then he rides down eight rows in the 300 metre-long greenhouse. The following week he changes the pattern and takes the eight rows in between.
The advantage of this method of dispersal is that the grower gets a good picture of the condition of his crop in a short space of time. “It means I can see straight away whether the plants are growing well and if there are patches of whitefly, spider mite or other pests remaining.”

Combining bio and pollen

This year, biological control is once again going according to plan. When the third crop starts, De Groot will be using a high dose of standard bags of swirskii, one for every two plants. He wants to keep this population vital until the end of the crop with supplementary feeding.
“We are noticing that supplementary feeding with the pollen preparation is adding a new dimension to our biological control. We’ve seen for ourselves how predatory mites can build up a good population when they get a varied diet, in other words a combination of pests and pollen. With more and more chemical pesticides being banned, I see this as a good strategy for the future,” Verbeek adds.


The number of sweet pepper and cucumber growers feeding predatory mites pollen preparations is on the rise. The varied diet of pests and pollen creates a good, resilient population of natural predators. Although this strategy means the money has to be spent before the benefits are felt, this trend looks set to continue.

Text and images: Pieternel van Velden.

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