Whether they are used in a preventive or a curative approach, parasitic wasps and gall midges are the cornerstone of a reliable aphid control strategy. For cucumber and gherkin growers, now is the time to act, advises Biobest.
Due to the nice weather, spring has awakened rapidly this year. It is also time of the season for aphids, which are now starting to invade greenhouses in Western Europe, it said in a press release.
For cucumber growers, aphids are among the most problematic pests. With a new cultivation period starting soon, Biobest strongly advises taking action now.
Biological control of aphids rests mostly on the introduction of parasitic wasps and gall midges. The female insects look actively for aphid hot spots to lay their eggs. When these eggs hatch, the larvae devour the aphids, it said.
How can growers know which beneficial they should introduce and when? “It depends on whether the grower knows exactly which species are present in his crops,” said Wesley Akkermans, sustainable crop management specialist at Biobest.
Cotton aphid (Aphis gossypii)
“If he has only spotted small aphids, like the green peach aphid (Myzus persicae) and the cotton aphid (Aphis gossypii), he can rely on two parasitic wasps as part of a curative strategy: Aphidius colemani, complemented with Aphidius matricariae. However small, these aphid species are notorious for their rapid distribution.”
For bigger species, like the glasshouse potato aphid (Aulacorthum solani) and the potato aphid (Macrosiphum euphorbiae), Akkermans advises the use of Aphidius ervi and Aphelinus abdominalis. “The parasitic wasps are always introduced as mummies. These need to be put on damp, shady spots between the crops to guarantee the best result, preferably close to an aphid hot spot”
If growers don’t know which aphid species are present, or if they want to maintain a thorough preventive strategy, they can opt for Biobest’s Aphi-Mix-System. This is a mixture of the four above-mentioned Aphidius species in the same package.
Last but not least, the parasitic gall midge Aphidoletes aphidimyza is a strong complementary weapon against aphids. In contrast to the parasitic wasps, the gall midge isn’t very choosy regarding its diet. “Its progeny eats literally every aphid species,” Akkermans said. “Moreover, thanks to the large cucumber leaves, the larvae have an excellent mobility. Only a few larvae per leaf is already enough to destroy a complete aphid population.”
Because of this complementarity Akkermans strongly recommends to apply the gall midges in combination with the parasitic wasps.