Biological control tackles the major challenge of aphids

In several crops, including sweet peppers, aphids are growers’ number one pest problem. With the withdrawal of chemical crop protection products and the emergence of resistance, biological control has become increasingly important in recent years. Biobest offers the broadest range of biological control agents on the market. “With this extensive portfolio, growers can effectively tackle aphids.”

While tomato growers rarely experience problems with aphids, they are generally the biggest pest challenge in sweet pepper cultivation. Aphids produce large amounts of honeydew, making the fruit sticky and eventually unmarketable. When aphid populations become too high, plant growth can also stop, and the greenhouse climate in affected areas may be negatively impacted. In short, growers have every reason to control aphids, but achieving this is far from straightforward today.

Conflict with MRL requirements

“The problems started when Plenum was withdrawn from the market,” explains Marvin Koot, crop protection specialist at Biobest. “That was almost five years ago. Until then, growers had a tool that allowed them to keep aphids well under control. Alternative products were either incompatible with biological control or caused problems with MRLs, the maximum residue limits for vegetables and fruit.”

These challenges forced growers to rely more heavily on biological control.

“Until two years ago, this was still relatively manageable with a combination of biological control and limited chemical treatments,” says Koot, who mainly works with vegetable growers. “Then, two years ago, a resistant aphid appeared. At that point, there was still an emergency solution available: a product against thrips that also proved effective against aphids. However, it became increasingly clear that we needed to find a long-term biological solution.”

A major challenge

Biobest had already anticipated several years earlier that aphid control would become a major challenge without an effective biological solution. The company invested heavily in research, enabling it to introduce several new products in recent years.

“These include two hoverfly species, Eupeodes-System and Sphaerophoria-System. Two years ago, we added the brown lacewing, Micromus-System, and this year the ladybird, Propylea-System.”

At the time of their introduction, much was still unknown about these biological control agents. When should they be released for effective control? And at what application rates? These questions had to be answered through practical experience.

“There simply wasn't enough time to establish all the details during the research phase,” explains Koot. “Fortunately, Dutch growers understand this. Together, we started developing the right strategy to maximise biological aphid control.”

Another piece of the puzzle

Koot is clear about the success of this approach.

“We've made significant progress. Most growers now only use chemical treatments as a corrective measure in emergencies, whereas previously they would routinely spray every few weeks. With Propylea, we've added another piece to the puzzle of biological aphid control.”

One advantage of Propylea and Micromus is that they can be introduced as adults and immediately start feeding on aphids. This makes them particularly effective at tackling aphid hotspots.

They also work very well in combination with the widely used parasitoid wasp Aphidius colemani and the predatory gall midge Aphidoletes aphidimyza. Both have excellent searching behaviour and can locate the first aphids in a crop.

“Another advantage of Propylea is that it can sustain itself,” says Koot. “It also feeds on pollen, so it isn't entirely dependent on aphids being present in the crop.”

Alongside Propylea and Micromus, hoverflies are used as part of a broader control strategy.

“They perform better under certain conditions. By combining these different biological control agents, growers can keep aphids effectively under control.”

However, Koot emphasises that scouting is becoming increasingly important.

“Early detection is essential. As soon as you spot aphids, you need to introduce biological control agents directly into those areas.”

Koot expects more intensive scouting to become the new standard.

“We're gradually seeing greater awareness of this. Leading growers employ staff whose sole responsibility is continuous scouting. We also see that these companies are often willing to tolerate slightly higher aphid populations in their crops. You need a certain number of aphids to keep biological control agents active. That means occasionally accepting a sticky fruit.”

No chemical treatments needed

One company that is willing to introduce biological control agents in substantial numbers is Seasun, based in Kapelle, Zeeland, the Netherlands.

Despite experiencing aphid pressure, the company has not needed to use any chemical treatments in its sweet pepper crop this year.

“We've been working with biological control for a very long time, but we've intensified our approach in recent years,” explains Alex Gresnigt. “This is mainly because chemical products are often no longer sufficient. We try to rely on biological control as much as possible.”

Seasun is using Propylea for the second year.

“It's a voracious predator that we can use effectively alongside hoverflies whenever we detect an aphid hotspot. In addition, we release parasitoid wasps and predatory gall midges almost every week.”

Intensive scouting is an essential part of the strategy.

“We continuously have four scouts working in the greenhouse. They monitor and record everything they observe. This gives us a clear overview of the greenhouse and the location of pest populations. Data is extremely important for effective pest management.”

So far, Seasun's experience with biological aphid control has been positive.

“We occasionally have some sticky fruit, but what we notice most is that the biological control agents completely clear aphids from infested plants. Our goal is to reduce the number of sticky fruits to zero. That is only possible through intensive scouting. The earlier you detect aphids, the better you can respond.”

Gresnigt is convinced that biological control is the future.

“More and more growers are starting to realise this. Eventually, all chemical crop protection products will disappear from the market. We'll continue looking for the best solutions, but for now, we're pleased to have achieved a biological balance in the greenhouse.”