Protecting Crops from Deer Damage

Technical articles - Insectes et ravageurs

Arboriculture et petits fruits Arboriculture et petits fruits Viticulture Viticulture

Browsing, bark stripping, rubbing,… the damage caused by roe deer and red deer can be very significant in crops and detrimental to the economic health of the farms that suffer them. Here is an overview of the means of protecting crops against cervids.

Damage

Browsing

This feeding behavior of cervids is a supplement to their herbaceous and semi-woody diet. It consists of removing buds, twigs, and branches within the animals' reach. The absence of upper jaw incisors prevents cervids from shearing shoots. They grasp young shoots by pinching between the incisor pad and the lower jaw incisors. This feeding mode gives the almost horizontal wound a chewed appearance.

Vigne abroutie

Identification of the damage perpetrator is based on:

• The height of the wound above the ground:
  • Roe deer: up to 1.10 m,
  • Red deer: up to 1.50 m.
  • Specific conditions may increase these maximum values: thick snow cover, steep slope, possibility for the animal to stand on its hind legs.
• Examination of presence signs (tracks, droppings, hair) near the browsed plants.
• Although cervids tend to cause damage throughout the year, two preferential periods are observed:
  • At the end of winter: food resources are minimal and scarcity is even more marked during prolonged snow cover.
  • At spring budburst: young tender shoots constitute a fresh choice food after the poor winter diet based on lignified shoots.

Bark stripping

Bark stripping is a mixed act of feeding and behavior (caused by excessive disturbance of individuals, including tourism, winter sports, stray dogs) attributable to the red deer. It consists of gnawing the bark which is then entirely consumed.

• Tooth marks are clearly visible, side by side and separated by cambium remains.
• This debarking can be located around the entire circumference of the stem.
• Bark stripping mainly concerns trees pruned with a diameter greater than 10 cm at 1.50 m high.
• The bark stripping phenomenon mainly occurs during the winter period.
• The width of tooth marks on the cambium is 8 to 9 mm for red deer, 4 to 5 mm for roe deer.
• The height of the damage relative to the ground is between 100 and 170 cm for red deer, between 50 and 70 cm for roe deer.

Rubbing

Rubbing is a behavioral act consisting of cervids rubbing their antlers on tree trunks and stems.

The wounds are observed during the shedding period when animals rub their antlers to remove velvet, or during the rut period when rubbings serve to mark territory :

• The shedding rubbings are generally mild and located on one side of the stem. They occur from late July to late August for red deer, and from April to May for roe deer.

• During the rut, rubbings are much more aggressive as males engage in real substitute fights against young trees to discharge their aggression, leave olfactory signals, or mark their territory. Given this excitement, rut rubbings result in deep marks on stems, bark stripping around the entire stem circumference, and many broken branches. The roe deer rut occurs in summer, from mid-July to mid-August, while the red deer rut takes place in September – October (rut).

Attribution of damage to roe deer or red deer is based on:

• the size of the plant: stem diameter less than 3 cm for roe deer, 3 to 5 cm for red deer, although larger stems can also be affected.
• the height of the damage: the attack zone is between 20 and 80 cm high for roe deer, around 100 cm on average for red deer, even reaching 180 cm.

Direct protection means

Individual protections

These plastic nets measure between 0.60 and 1.20 m high and 15 to 30 cm in diameter. They must be systematically supported by stakes and be strong enough to withstand cervid attacks.

There are many individual protections against large game:

• Sleeves
• Wire mesh sleeves
• Tubes
• Iron tree
• Bud protector clip
• Protection net against bark stripping
• Spiral plastic band against bark stripping

Advantages

• Competitive cost for low-density planting
• Free movement of game and maintenance of feeding capacity
• Facilitates spotting small plants in vegetation

Disadvantages

• High cost for dense plantations or large areas
• Not fully effective
• Risk of plant deformation, rotting, or embedding
• Requires fairly regular monitoring
• Visual and environmental pollution
• Mandatory removal

Find a comparison of individual protections here.

Electric fences

Electric fencing is a proven means of preventing large game damage. Its operating principle is simple: upon contact with the fence, the animal closes an electric circuit and receives a deterrent, non-lethal shock. It quickly learns that contact with the wire triggers pain. By conditioned reflex, the fence becomes a no-touch zone, an obstacle not to be crossed.

Fence device against red deer.

There are 3 types of devices:

• Mains-powered energizers: they provide higher energy output, electrify long wire distances at low operating costs, and require little maintenance. Generally, mains-powered models are intended for permanent fences.
• Battery-powered energizers, also called accumulator energizers: intended for temporary or isolated fences (no mains access). To avoid frequent battery recharging, a solar panel can be connected to the energizer.
• Battery energizers: often less powerful, intended for shorter temporary fences or applications requiring frequent energizer moves. They are less effective against large game (lower practical electric shock).

For large game, the key is to have a load voltage under 500 ohms (a more reliable criterion than output voltage) of at least 4,000 volts across all installation wires.

The number of conductors and their height above the ground depend on the animals to be kept out:

• Roe deer: 4 conductors at heights of 30, 60, 90, and 120 cm.

• Red deer: 6 conductors at heights of 30, 60, 90, 120, 150, and 180 cm.

Advantages

• Competitive cost for high-density planting and large areas
• Durable physical barrier against all types of damage
• More effective protection against red deer than individual protection

Disadvantages

• High cost for small plantations and low plant density
• Deprives game of part of its territory and intensifies damage elsewhere
• Territory fragmentation
• Needs removal

Indicative cost

For a device against red deer (6 round aluminum wires 2 mm diameter, battery energizer, two batteries, treated spruce stakes every 20 m, other rebar stakes every 5 m), the cost of such a device is:

• €1,200 for a 1-hectare square plot
• €2,000 for a 5-hectare square plot, i.e., €400 per hectare.

For more information on electric fence costs, consult this document.

Wire mesh fencing

This is a mechanical device woven, braided, or welded, preventing animals from accessing the threatened area. It consists of hexagonal, square, or rectangular mesh fixed on wooden, concrete, or metal tube stakes.

The technical characteristics depend on the animal to be protected against.

Wire mesh fencing against large game mostly relies on fences with "ursus" mesh and wooden stakes. The mesh, knotted or welded, is supplied in rolls of variable length, often 50 m.

Protective mesh against deer.

Choosing galvanized mesh is preferable because aluminum and zinc galvanization guarantees the product a long service life. Rectangular mesh is recommended for large game fences. Wire diameter ranges from 2 to 3 mm for wild boar and red deer, and from 1 to 2 mm for roe deer. It is recommended to use mesh with thicker edge wires to ensure better strength and longer durability.

The durability of wooden stakes varies according to species and treatment:

• round treated spruce stakes in autoclave: 10 to 15 years;
• split oak stakes: 15 to 20 years.

Fence typology must adapt to the target species:

• Roe deer:
  • Mesh height of 150 cm, wire diameter 1 to 2 mm, with a maximum mesh size of 15 cm.
  • Stakes height 180 to 200 cm, diameter 8 to 10 cm.
• Red deer:
  • Mesh height 200 to 220 cm, wire diameter 2 to 3 mm, with a maximum mesh size of 15 cm.
  • Stakes height 220 to 240 cm, diameter 9 to 11 cm.

Advantages

• Competitive cost for high-density planting and large areas
• Durable physical barrier against all types of damage
• More effective protection against red deer than individual protection

Disadvantages

• High cost for small plantations and low plant density
• Deprives game of part of its territory and intensifies damage elsewhere
• Territory fragmentation
• Needs removal

Cost

As an indication, a 50 m roll of heavy 3 mm diameter "ursus" mesh costs about €200, and wooden stakes cost between €2 and €6 each. These amounts must be increased by installation costs, for example by a contractor. Overall, the cost of a fence with "ursus" mesh ranges from €8 to €20 per linear meter, depending on length, materials chosen, and terrain conditions.

Repellent products

These products have a repellent effect by acting on animals' sense of smell, taste, or simply mechanically. Depending on the case, their application is done:

• on animal paths (e.g., cloth soaked and tied to a fence) to deter them from entering a plot or building.
• on terminal shoots of trees or young plants, by brushing or spraying, to discourage animals from browsing.

Products on the market

There is a product on the market based on sheep fat, which, due to its bad smell, repels cervids from crops. Easy to use, this product, called Trico, is a natural-origin repellent categorized as a "biocontrol product".

Product composition:

• Extracts of sheep fat, to which a white marker has been added, an emulsifier to make it water-miscible, and a fixative to ensure lasting effect.

Diffuser

Product use:

• Preventive use: Place diffusers on concerned plots. For 50 to 80 diffusers per ha, the volume of pure product will be 2.5 liters (5 cl per cup), provided it is applied only once.
• Curative use: By spraying, Trico is applied at a dose of 6 ml of spray mixture per vine. Since the product is used diluted, it is estimated that between 3 and 5 liters of pure product are needed to protect one ha of vineyard (price per liter €18 excluding tax). The spray mixture (about 20 liters/ha) is distributed with a backpack sprayer on vegetation at the 2-3 leaf stage. To ensure sufficient barrier, it is advised to cover one-third of the planted surface (the first two border rows, focusing on entrances). At the indicated concentration, one application suffices. The product's persistence duration, 40 to 45 days, gives fruiting shoots time to develop enough to resist cervid attacks.

Advantages

• Quick application

Disadvantages

• Expensive, requires renewal within the year
• Like most repellents, risk of habituation

For more information on this product, consult this datasheet.

Sheep wool

It has been observed that roe deer do not venture into territories frequented by sheep herds. They seem bothered by the smell and the large swarm of flies accompanying sheep. It therefore seems interesting to scatter wool on vegetation.

Placement:

Placed around plants or on young trees, untreated and unwashed sheep wool is used as a repellent, by its smell and texture, to keep cervids away and allow young shoots and/or trees to grow:

• in scattered piles
• at the foot of plants
• on the branch crown

Advantages

• Free
• Environmentally friendly
• Does not prevent game movement

Disadvantages

• Quite time-consuming to place

Hair

Placed as balls 10-15 cm in diameter inside stockings or tights, scattered around the plot.

Advantages

• Easy to place
• Environmentally friendly

Disadvantages

• Effectiveness over time to be tested

Other artisanal methods

Other odorous products have been tested by farmers and are apparently effective in repelling game but have not been experimentally verified:

• Perfume
• Guano
• Predator droppings
• Predator urine
• Soap or soapy water: some hang soap bars on trees or stakes.
• Chili or bell pepper: some prepare a diluted spicy sauce and spray it on trees and plants; the emitted odor irritates cervids.
• Egg: some use a spray solution based on eggs (80% water with 20% egg). The smell of egg decomposition would deter deer by associating decomposition and rot odors with predators. This solution is applied every 30 days or after rain.

Advantages

• Free if materials are available
• Easy application depending on packaging

Disadvantages

• Effectiveness over time to be tested, may dilute with rain
• Not always environmentally friendly

Scaring systems

Sound scaring

By repeated emission of various noises, an insecure environment is created to keep animals away from the risk zone. Several systems exist: radio, loudspeaker, gas cannon, flare shots or whistles, ultrasounds, siren, etc.

Despite irregular sounds, wild animals are quite good at understanding after a few days that there is no real danger: this is habituation. Acoustic scaring is reserved for areas far from dwellings to avoid disturbing nearby residents.

To discover models of sound scaring devices, consult this site.

Advantages

• Sound scaring devices are effective.
  

Disadvantages

• Cost

• Effectiveness over time to be tested.

Visual scaring

It consists of using various objects to frighten animals: scarecrow (dummy), shiny objects (CDs), plastic bags, etc. The equipment is placed on plots to protect or around their perimeter. Moving devices would be more effective but animals get used to them after a while.

Visual scaring of deer by streamers

Placing streamers on fences would temporarily protect sensitive productions (cereals) against cervids. Highly visible, these streamers flutter and make noise at the slightest wind.

Advantages

• Easy to implement
  

Disadvantages

• Cost
• Effectiveness over time to be tested.

Shooting

Hunting, which allows population regulation, is at the heart of the game damage prevention system.

Since 1979, hunting plans are mandatory. They are issued by order of the Prefect of each department, after advice from the departmental commission competent in hunting and wildlife matters, in line with the Departmental Game Management Scheme. They are established for a period of up to 3 years, subject to annual revision.

Compensations

The compensation procedure by the departmental hunters' federation operates within a well-defined framework. All types of crops are concerned by the big game compensation: vineyard, wheat, corn...

Some conditions to be met:

• being a farmer,
• damage only from big game coming from neighboring lands (not farmed by the tenant),
• minimum damage of 3% of the plot area (or minimum damage of €230 or €100 for meadows).
• To request compensation, the damage must be assessed by an expert from the Hunters' Federation; the harvest takes place only afterward.

From the receipt of the damage declaration, the Hunters' Federation has a maximum period of 8 days to carry out the assessment. Only damage caused to crops, to the inter-rows of perennial crops, to harvest nets, or to the harvest itself is compensated.

The compensation file: to be requested from the Hunters' Federation and completed without delay (before harvest), as thoroughly as possible, and sent to the Federation.

The compensation procedure: assessment within 8 working days.

• The expert establishes a final report in agreement with the farmer, transmitted within fifteen days to the Hunters' Federation.
• In case of dispute by the farmer, the file is forwarded to the departmental Commission for Hunting and Wildlife (compensation commission).
• If the assessment is accepted, compensation is paid by the Departmental Hunters' Federations shortly after the prefectural decree setting the rates for the concerned crop has been issued.

Calculation of compensation: based on a departmental scale negotiated each year.

A legal deduction of 2% is applied. An additional reduction (which can reach 80%) may be applied if the farmer bears some responsibility for the occurrence of the damage (encouraging the arrival of game, refusal of prevention methods proposed by hunters).

Cette technique s'applique aux cultures suivantes

• Apricot
• Hazelnut
• Walnut
• Pear
• Apple
• Plum
• Peach
• Vine

La technique limite la présence des auxiliaires et bioagresseurs suivants

• Cervids