Keep wireworm in check during seedling growth

The maize season is upon us. Those hoping to grow maize, whether maize silage or maize grain, will face major challenges this year.

A wide variety of traditional seed dressings are no longer available as the neonicotinoids they contained to regulate disease in maize have had their legal approval rescinded. As a result, pressure from diseases such as corn smut, rootworm and the frit fly is ever increasing. Farmers are increasingly worried about wireworm in maize, since the seed, seedlings, roots and young plants are all susceptible to this pest.

We’ve pulled together a summary of the reasons for this and what preventive measures are available.

Why wireworm is a problem for maize

Wireworms are the larvae of the click beetle.

From May through to the beginning of August, click beetles lay their eggs on or just below the soil surface in nests irregularly distributed across arable land. They prefer moist soil and undisturbed locations. Approximately one month later, the pale-yellow larvae hatch. They are about 1.5 millimetres long at this stage.

In their first year, wireworms are mostly harmless. They reach their true pest potential only the following year, immediately after maize is sown through to roughly the end of April. Plants at this time of the year are in the very early stages of development and are not yet fully grown.

Larvae are about 3-4 centimetres long at this point and have developed a chitinous shell making them very resilient. Seeds, seedlings and young stems are all at risk. They also like to nibble on young plants. Larvae have the potential to eat through entire plant stems, thus separating the roots from the rest of the plant.

They pass through several larval stages spanning 3 - 5 years, meaning the cycle is repeated over the following years. Click beetles lay eggs annually, therefore several generations of wireworms and click beetles are often present in the same location at every stage of their life cycle.

Wireworm symptoms

Wireworms can cause enormous damage and plants often become unable to sustain themselves with the necessary nutrients after an attack, meaning they stop growing. This can result in stunted growth, and sometimes complete plant loss. A wireworm infestation in maize is outwardly visible through brown and wilted leaves, and affected plants can be pulled out of the soil with little effort.

Wireworms pose a serious threat to maize crops and in the worst-case scenarios, can cause complete plant loss.

Detecting wireworms

There are two methods to find out whether a field is infested with wireworms. Dig down to around 10 cm in the upper soil layers of the suspected wireworm location. Wireworms can then be identified with the naked eye. Bait traps offer a simpler method that uses potatoes buried at a depth of 10 cm in various locations. The potato halves can then be dug up one week later and checked for signs of feeding larvae.

The wireworm damage threshold in maize is 1-2 worms per square metre. It is very important to act immediately once this pest has been identified, as they are still relatively sensitive during the first larval phase. Once larvae have developed their protective shell in their second year, they become more difficult to manage and wireworm damage increases.

There are currently no clear findings or recommendations regarding how to control wireworms.

Caption: Neonicotinoid seed dressings are increasingly losing approval (Photo: agrarpress, Friederike Krick).

There is a deficit of effective maize seed treatments against wireworm

As a rule, seed treatments against wireworms are not approved in Germany. There are certain treatments which boast side effects that have been effective in the regulation of click beetle larvae.

Approval is gradually being rescinded for these treatments, however. The Mesurol seed treatment containing the active ingredient Methiocarb was banned in 2020, and the neonicotinoid seed treatment Sonido containing active ingredient Thiacloprid, will no longer be available from 2021.

What remains is the Force seed treatment with the active ingredient tefluthrin. However, this is by far not as effective as it does not offer complete plant protection. It only controls soilborne pests within a 3 cm seed radius. A maximum sowing depth of 3 cm is therefore recommended when using this agent for maize, rather than the conventional cultivation depth of 4 - 7 cm. Farmers are then presented with another problem since the shallow placement makes germination more difficult and can also encourage bird predation.

Agricultural wireworm measures

Agricultural measures can be lengthy, however these are necessary. Success is often only experienced after a few years. In the absence of plant protection products, it is crucial to prevent the spread of wireworms by taking appropriate preventive measures in the field.

Avoid cultivation after grassland has been tilled

Meadow and pastureland is the click beetle larvae’s natural habitat, which is why they are more prolific here.  Consequently, maize should not be sown immediately after tillage or on fallow land  - and should ideally not be sown in the following years either. Cultivation should follow a similar approach to potatoes since wireworms are also an issue in potato cultivation and cause significant damage.

Targeted tillage in infested areas

If tillage operations are timed close to when click beetles lay their eggs, females will find it difficult to find safe places in the upper soil layers. This will mean they will lay fewer eggs. The soil will also dry out meaning that eggs already laid and young larvae will dry out. Tilling the top 10 cm is usually sufficient to achieve this. Since the egg laying season lasts from April to the beginning of August, it is advisable to repeat this several times.

Aridity an advantage during maize planting

During seed drilling, it is important that the topsoil is sufficiently dry and warm to ensure rapid crop emergence. The soil temperature should be at least 8 degrees and poor weather conditions should be avoided. The higher the soil temperature, the faster plants can develop. At 10 degrees, maize needs about three weeks to emerge, however, at 16 degrees, the period from maize drilling to crop emergence is reduced to just 7 days.

Are there other preventive measures available?

Underfoot fertilisers containing calcium cyanamide cause wireworms to avoid growing seedlings. Fertiliser bands are placed 5 cm from maize grains and scare off these pests. This reduces the contact between larvae and seedlings and under favourable conditions, reduces feeding damage by up to 50 %. To achieve this effect, 150 kg/ha of calcium cyanamide must be used. Calcium cyanamide can also be mixed with DAP fertiliser (diammon phosphate), however, if the infestation is too severe, success decreases with underfoot fertilisation. Competition for food between the multitude of wireworms then tempts them to accept the scaring effect of the calcium cyanamide fertiliser and to migrate to maize plants despite the poor living conditions.

Organic fertiliser offers no decisive impact on the severity of the infestation and the extent of wireworm damage in maize.

Summary: It all comes down to the right combination

All possible agricultural measures must be taken to keep wireworms in check. Even though agricultural chambers and crop consultants offer limited recommendations regarding wireworm control, it is widely agreed that rapid field emergence and fast seedling development are of prime importance when dealing with this pest and others.

MAISGUARD: Using biostimulants against wireworm

SEEDFORWARD offers the MAISGUARD seed treatment to counter the increasing limitations of conventional seed treatments. This maize seed treatment has been developed without the need for synthetic chemical agents and is instead based entirely on plant ingredients. It takes a different approach to insecticides when dealing with wireworms and other pests. By making use of biostimulants, maize varieties treated with MAISGUARD can withstand pathogenic influences more successfully.

This is achieved primarily thanks to the so-called disease escape effect. This seed treatment accelerates the early stages of plant development, and the natural ingredients further seed growth, field emergence and young plant development. Rapid growth is crucial as young plants, in particular, are susceptible to disease, pests such as wireworm and bird predation. By progressing rapidly through this critical early phase, emerging seeds literally outgrow wireworms, guaranteeing the healthy emergence of a stable crop.

MAISGUARD offers maize plants a real chance to overcome wireworms and to become resistant when used in combination with accompanying agronomic measures, and when supplemented by underfoot fertilisation with calcium cyanamide depending on the prevailing conditions. This facilitates strong growth with low rates of failure.

Read more about MAISGUARD.

Find out more about how it works, and the yield results you can expect.


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