10–30% yield loss at two to three larvae per plant
Feeding by the larvae hampers the supply of water and nutrients to the plant. With two to three larvae per plant, LfL Bavaria expects yield losses of 10–30% in the long-term average.
The method
Trichogramma against the European corn borer
What damage the European corn borer does, how the parasitic wasps stop it in the egg, when they are applied and what official trials show. Every figure comes with its source and its date.
Damage
What the European corn borer does to your maize.
The damage is done by the larvae: they eat their way through stalks and cobs, weaken the plant and promote fungal infection. We have known this from our work in our operating regions since 2016, and the official advisory services describe it the same way.
Broken stalks, lost cobs
The tunnels weaken the stability of the plant. In LfL Bavaria field trials from 1997 to 1999, up to 25% of the stalks bent over in conventional varieties. Especially in years with frequent thunderstorms, the plants break low down, and a large part of the cobs can then no longer be harvested, even with row-independent harvesting methods.
More fungal infection, a risk to feed quality
By boring into the plant, the larvae promote fungal infection, above all by Fusarium species. These cause stalk and cob rot and, under certain conditions, produce mycotoxins such as deoxynivalenol (DON) or nivalenol, which considerably impair feed quality.
Spreading north
For 2026, the Lower Saxony Chamber of Agriculture reports particularly high pest pressure in regions with known infestation and, at the same time, a clear spread northwards. The European corn borer was originally confined to warmer regions such as the Mediterranean countries and the Upper Rhine valley. It first appeared in Bavaria at the end of the 1970s and since 2005 has been found on almost all maize fields there.
Tunnels from tassel to stalk base
The larvae bore into the maize plant. Their tunnels can run from the tassel stem down to the base of the stalk, and more are found inside the cob and between the kernels. How to spot an infestation: bent or broken tassels and frass in the leaf axils. The older the larvae, the further down they bore and the greater the damage.
How it works
The wasp stops the corn borer in the egg.
Trichogramma are tiny parasitic wasps whose young develop inside the eggs of other insects. Against the European corn borer (Ostrinia nubilalis) the method acts where no damage has been done yet: on the egg mass.
Parasitised eggs instead of boring caterpillars
Trichogramma females lay their eggs in the egg masses of the corn borer. Instead of a caterpillar that bores into stalks and cobs, a new wasp hatches from the corn borer egg. According to the LfL, the method does not harm other beneficials such as ladybirds.
Source: LfL Bavaria, Maiszünslerbekämpfung
As at: 8 October 2026 (accessed)
Smaller than a millimetre
Trichogramma wasps are only about 0.4 mm long. At 25 °C their development from egg to adult takes about ten days. The minimum temperature is 15 °C, and above 38 °C they lay no more eggs. One female can lay 70 to 120 eggs. In maize, the species Trichogramma brassicae is used against the corn borer.
Source: LWK NRW, Trichogramma-Schlupfwespen gegen Schadschmetterlinge
As at: 17 September 2020
Black eggs show it is working
The wasp larva feeds on the contents of the corn borer egg. At 24 °C parasitised eggs turn evenly black after about four days. On a walk through your field you can see for yourself whether the egg masses in your crop are parasitised.
Source: Hortipendium, Trichogramma brassicae
As at: 1 June 2016
Timing
Released at the start of the flight, once or twice.
The wasps have to be in the field when the corn borer lays its eggs. The date therefore follows the moth flight, which the official plant protection services monitor afresh every year. The three established schemes we offer provide for one, two or three applications.
Two dates, according to LfL Bavaria
According to LfL Bavaria, good efficacy requires the beneficials to be released at the start of the corn borer flight and again twelve to fourteen days later.
Source: LfL Bavaria, Maiszünslerbekämpfung
As at: 8 October 2026 (accessed)
Ten to 14 days, according to LWK NRW
The North Rhine-Westphalia Chamber of Agriculture recommends the first application at the start of the female moth flight. Repeating it after ten to 14 days improves control.
Source: LWK NRW on Ökolandbau NRW, Maiszünsler mit Wespen bekämpfen
As at: 26 June 2025
Forecasts and traps
ISIP Baden-Württemberg forecasts the start of the corn borer flight. The plant protection services monitor the flight with light and pheromone traps and record its start, its peak and larval hatching. ISIP places the best date for the wasps around the flight peak.
Source: ISIP Baden-Württemberg, Maiszünsler in Mais: Prognose und Befallserhebungen
As at: 8 October 2026 (accessed)
Our own traps and temperature stations
We also run our own traps and our own temperature stations. Their data supplement the data of the official services for us.
Source: TB Copters
As at: October 2026
Warmth, not the calendar
When the moths fly depends on warmth, not on the date. For the univoltine race, LTZ Augustenberg gives the start of pupation at about 200 degree-days, the start of the flight at about 350 and its end at about 650 degree-days. The bivoltine race in the Upper Rhine valley needs much less warmth and produces two generations a year.
Source: LTZ Augustenberg, Auftreten der bivoltinen Rasse des Maiszünslers in Baden-Württemberg (poster)
As at: 2012
How long the wasps keep hatching
The wasps do not hatch from a capsule all at once but in several staggered waves, according to the manufacturers over a period of up to three weeks.
Source: Manufacturer information (Biocare, AMW Nützlinge, AGROLINE)
As at: 9 October 2026 (accessed)
One application or two
The moth flight can last longer than the hatching from one capsule. For silage and grain maize the manufacturers therefore mostly plan two applications 10 to 14 days apart, and LfL Bavaria also recommends two dates. There are also products for a single application with a higher count.
Source: Manufacturer information (AMW Nützlinge, AGROLINE, Biocare); LfL Bavaria, Maiszünslerbekämpfung
As at: 9 October 2026 (accessed); 8 October 2026 (LfL, accessed)
Efficacy
What official trials show.
Each result stands here with its source and its date.
LTZ Augustenberg
In trials from 2009 to 2015, LTZ Augustenberg measured an efficacy of about 71%. According to LTZ, that is only just under 10% below the efficacy of chemical plant protection products.
Source: Kansy and Zimmermann, Landinfo 4/2016 (LEL Baden-Württemberg)
As at: 2016
On-farm trials in southern Europe
In two-year on-farm trials in southern France, northern Italy and Slovenia, Trichogramma protected the maize comparably to conventional control. Mycotoxin levels in maize destined for food stayed below the EU maximum level in these trials.
Source: Razinger et al. 2016, Pest Management Science 72(2):246–254, DOI 10.1002/ps.4054
As at: 2016
Application
Capsules, spread from the air.
How the wasps get into the field decides the effort and the crop damage. Which of the three established schemes we offer suits your farm is set out on our services page.
Carriers on the market
Trichogramma are sold on cards or in capsules. Cards are hung on the plants by hand; capsules are thrown into the crop. According to the North Rhine-Westphalia Chamber of Agriculture, cards suit smaller areas and capsules larger ones, and capsules can be applied from the air by multicopter.
Source: Hortipendium, Trichogramma brassicae; LWK NRW on Ökolandbau NRW
As at: 1 June 2016 (Hortipendium); 26 June 2025 (Ökolandbau NRW)
Our capsules
Our multicopters apply capsules, 100 capsules per hectare and application. Custom fillings are available on request, for example with a different number of eggs. The shells break down in the field. Hanging cards cannot be applied by drone; they are hung by hand.
Source: TB Copters
As at: October 2026
What speaks for the drone
A study of applying Trichogramma from the air names the quick response to an infestation and short application times over large areas. Add what the drone itself brings: no soil compaction from the drone and no wheel damage in tall maize.
Source: Bzowska-Bakalarz et al. 2026, Agricultural and Forest Entomology 28(3):471–482, DOI 10.1111/afe.70049
As at: 2026
Legal framework
Non-chemical methods come first.
Integrated pest management in the EU
Directive 2009/128/EC obliges the Member States to ensure that all professional users apply the general principles of integrated pest management set out in its Annex III. Under them, biological, physical and other non-chemical methods are to be preferred to chemical ones if they provide satisfactory pest control.
Source: Directive 2009/128/EC, Article 14 and Annex III (EUR-Lex)
As at: 26 July 2019 (consolidated version)
Next
From knowledge to the operation.
Dates, application schemes and answers to common questions are on our services page.