Protecting Corn Seedlings from Corvids

In the corvid family, there are the rook, the crow, and the jackdaw. Following the cessation of seed treatments based on thiram, corvids are the main pests of corn crops. Faced with this difficult-to-predict and control risk, certain precautions are recommended during crop establishment.

Risk Period

The main predatory corvid species are the carrion crow and the rook. These corvids consume corn seeds from sowing until the 4-5 leaf stage, and occasionally up to the 7-8 leaf stage.

Following the sowing line, they are capable of causing significant damage, potentially leading to re-sowing. The intensity of attacks depends on the dietary needs of these birds linked to their reproduction, from late April to late May, and the food availability in the environment, which corresponds to corn sowing and seedling stages.

Corvids are strongly present in areas with nearby refuges (woods, large trees, nesting in parks…). They do not like to be disturbed. Thus, the most at-risk plots are those with less human presence (large plots, elevated plots with clear views, isolated plots).

Moreover, an area with only a few corn plots is more exposed to corvid risk than a sector where sowing occurs simultaneously over large areas (dilution of supply). This is why their presence is often reported in regions where corn cultivation is minor.

Control Methods

Let's be clear right away, there is currently no single truly satisfactory solution BUT a combination of levers will help limit the impact of these attacks on sowing.

Agronomic Levers

The preferred strategy is to sow under the best possible conditions to promote rapid emergence and growth. It is recommended to combine several levers:

Avoid staggered sowing and be careful with isolated plots. As much as possible, it is preferable not to sow plots too staggered, i.e., too early or too late compared to the nearby environment.

Properly firm the sowing line for better anchorage and a harder surface (a seedbed that is too cloddy with many residues can facilitate seedling uprooting by birds).

Be vigilant about sowing depth by not sowing too shallow; ideally, sow at 4-5 cm depth or more. Shallow sowing (2-3 cm) is a risky practice favoring seed grasping.

Sow with reduced spacing (40-50 cm) for visual disturbance (more rows imply dilution of attacks).

Associate bait plants (cereals). The use of false sowing can be very effective in fighting crows. Sowing corn under a cover of wheat or simultaneously with wheat sowing can be very effective. Indeed, wheat serves as a bait plant to deceive crows in their search for food. Young wheat shoots are just as attractive to pests, which helps protect the real crop. Find a testimony here.

Use quality seeds with biostimulants. Several seed companies indicate they are working on this and hope to offer alternatives soon.

Protect the crop against soil insects because crows preferentially attack plants colonized by wireworms.

Other solutions are cited in the field but with unmeasured effectiveness such as Avifar (game and bird repellent), post-sowing application of quicklime at 300 kg/ha, or seed coating with milk or chili pepper before sowing.

Seed pelleting: To make seeds less visible to birds, it is possible to pellet them with a mixture of components such as clay, vermicompost, molasses,... There is no repellent effect; birds simply do not see the seeds on the surface, so they do not consume them. There is also no effect on germination; it will occur when the seed has enough moisture to germinate. Nevertheless, this technique will help accompany the seeds in their development.

Agronomy reduces exposure to risks, but in the face of strong attacks, this is unfortunately not always sufficient. To limit pressure, other control methods can be considered.

Physical Control

Crow Traps

Crow traps are generally large metal cages with a particular shape. The upper part is directed towards the sky and shaped like a V (the V pointing inward). The objective is to make corvids enter through the bottom of the V, which has a one-way mechanism. For optimal effectiveness in trapping pests, the cage should be placed at the edge of the field to be protected and food placed inside to attract corvids.

Scare Devices

Scare devices should be moved regularly within the plot to prevent birds from getting used to their presence.

You can find several of the scare devices listed below on the website of the company Agriprotech.

Kites

These are the most used against corvids; they are shaped like a predator. They generally have a large wingspan (about 1.2 m) which gives them visibility and credibility with pests. The goal of this type of scare device is to imitate the flight of a raptor hunting its prey.

The kite’s erratic and sudden flight creates a stressful and seemingly dangerous environment for unwanted birds. To optimize the use of this protection against pests, it is recommended to place the object in the plot and move it regularly every 4-5 days to avoid habituation by pests. Birds are intelligent and get used to the threat over time. Moreover, it is possible to install several on the same plot (depending on the area) to increase the coverage of these systems.

Indicative price incl. tax: €50-85 each.

Helium-filled Balloons

The difficulty of this technique is finding robust balloons suitable for long outdoor flight. Aluminum foil balloons are preferable to latex balloons because they do not become brittle under the sun and are easier to reinflate. However, they may burst in strong heat. Attach 3 to 4 balloons per hectare at the end of a fishing line or nylon thread (strength > 5 kg) 15 to 20 m long. Changing the balloon locations every 3 to 4 days can increase the method's effectiveness. Balloons must be reinflated every 3 to 5 days. To prevent crows from getting used to the balloons too quickly, they should only be installed when damage risk exists.

Indicative price incl. tax: €50-85 each.

Large Bags Mounted on Stakes

Recycling is perfect for this; you can use bags from inside big bags or old tarps. They must be moved regularly because crows get used to their presence.

Scarecrows

They must be moved regularly because crows get used to their presence.

The effectiveness of these passive scare devices can sometimes be disappointing due to rapid habituation by birds. Regular human presence often remains the most effective way to prevent establishment of crows in the plot.

Gas Cannons or "Bazookas"

Beware of neighbors! Gas cannons create a loud detonation intended to scare pests like pigeons or corvids. The principle is to release gas from a cylinder into a chamber with a valve until a certain pressure is reached, then release and ignite the gas with a spark to create a detonation. Hence the name bird cannons. The detonation occurs in a tube to concentrate the explosion and direct the sound where desired.

For maximum effectiveness, the cannon should be:

Positioned against the wind so it stays in place and the detonation does not resonate too far.
Not aimed toward dwellings and, if possible, placed at a minimum distance of 300 meters from them to avoid neighbor complaints.
Set for the desired detonation type (random or double shots) and the interval between detonations (usually 10 to 20 minutes).

In France, there is no regulation concerning the use of scare cannons, but prefectural or municipal orders may regulate their use. Moreover, noise pollution from these devices is regulated by public health code provisions, notably articles R. 1336-6 to R. 1336-9, which set noise limits related to professional activities. Under these provisions, the cannon can be equipped with a digital timer to automatically shut off during night periods (from 10 p.m. to 7 a.m.).

A drawback of this practice against crows is theft and damage. It is common for a cannon or gas bottle to be stolen...

Indicative price incl. tax: €469 - 1860 each

Devices Emitting Sounds or Calls

There are acoustic devices emitting frightening sounds for birds: calls of raptors or distress calls. These are commercially available and can be easily installed. Depending on the calls broadcast, their effect lasts for varying durations.

Corvids are intelligent birds that quickly get used to different scare methods, so they must be implemented at the right time and alternated to be as effective as possible.

Indicative price incl. tax: €350-450 each

Lasers

Birds perceive the movement of the green dot of the laser beam projected on the ground as a danger and react on their survival instinct. They identify this movement as a threat but cannot understand what it is. Eventually, they leave the area. This technology is completely silent, making it an alternative to sound scaring near dwellings.

Various models are available at different price points, from torches to autonomous plot devices. They allow targeting individuals, but little information exists on effectiveness on groups of pigeons and corvids.

Drones

To prevent corvids from settling and nesting near the plot. Be sure to follow the regulations!

For more info, consult the overview of main scare device models by Terres Inovia.'

Encourage Natural Predators

Installing perches in the middle of plots will encourage the presence of raptors predators of corvids such as the common buzzard, kestrel, Eurasian sparrowhawk, or northern goshawk.

Here are some tips for building raptor perches:

For the best panoramic view, raptors must perch as high as possible: the perch post (usually wood) should be at least 2 m high (up to 3 m).
It must have a horizontal part so a raptor can perch without slipping.
Secure it well: fixed in the ground (40 to 50 cm deep) or with a tripod system.
Choose the right location: away from road edges, in a quiet area "infested" by predatory birds.
Multiply perches and space them every 2 or 3 ha.

Chemical Control

The only currently approved solution (Korit 420 FS – under derogation –) does not allow managing the "crow risk": according to Arvalis, "its effectiveness is (…) relatively satisfactory in low attack situations, but strongly limited as soon as corvid population pressure becomes significant"^[1].

Biostimulants

To be applied as a coating mixed before sowing. For example, PC21 from Elaf-Solutions.

Shooting

It is possible to regulate pest populations by asking hunters to shoot crows. In case of damage on a plot caused by crows, a shooting authorization must be requested. The hunting period can then be extended until July 31. This must be done through an individual prefectural authorization issued by the DDTM (Departmental Directorate of Territories and the Sea).

However, before requesting authorization to shoot crows or carrion crows, a scaring system must be implemented. Note that shooting is only allowed during the day with approved and declared weapons. Nest shooting is prohibited as is the use of dead decoys.

As a reminder, the rook and crow are classified as game species and considered likely to cause damage. Control can therefore start very early. National regulations then allow trapping (all year) and shooting (at certain times of the year) in most departments. Be sure to check conditions in your department, as regulations frequently evolve on this subject.

The jackdaw, however, is a protected species. Regulation measures may nevertheless be authorized locally through prefectural orders specifying the number of individuals that can be taken.

The use of several of these tools simultaneously is recommended to increase effectiveness on the same plot. Moreover, each device is placed at a specific location in the plot, so they do not cover the entire area potentially targeted by crows. The scope of your overall corvid control system can thus be improved by combining several of these tools.

Alert

Since attacks do not only occur at the plot scale, it is important to report all damage to your plots caused by corvids (even if you reported damage in previous years) via forms provided by departmental organizations: DDT, Chamber of Agriculture, FDSEA, FNC depending on department, town hall,... to have a complete overview of the situation and so that control actions can be conducted by authorized hunters or trappers to limit risk in following years. The effectiveness of these actions is long-term.

Even if reporting does not entitle compensation, the census of damage caused by bird species (or lack of reporting) is taken into account for their classification or not on the list of harmful species.

Sources

↑ Publication Choisir maïs ravageurs 2019

Appendices

[1] Publication Choisir maïs ravageurs 2019

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