Maine Apple IPM Prgram

Assessing Deer Damage in a Commercial Orchard

Formulas: William G. Lord, University of New Hampshire Cooperative Extension
Presentation: Glen W. Koehler, University of Maine Cooperative Extension

  
Introduction
    For this deer damage assessment, a block should be considered to include only trees of like cultivar, tree size, and age. Divide the orchard block into roughly equal sized sections. Each section should be no larger than about 1 acre. Select a single tree from the middle of each section.  Late March to early April is a good time to assess deer feeding damage.

    Do steps 1 - 3 for each sample tree.

STEP 1
    Calculate the Percent Canopy within Deer Browse Zone

    a) Measure the distance from the trunk to the edge of the canopy at 6 feet above the ground. We will call this "D6".

    b) Measure the distance from the trunk to the edge of the canopy at the bottom of the canopy. We will call this "Dbottom".

    c) Measure the height of the canopy area, (not the total tree height). We will call this "CH".

    d) Calculate the percentage of the tree canopy that is within browsing range of deer by using this formula:

Percent Canopy within Deer Browse Zone
=  100%  –    (D6) x (D6) x (CH – 4) x 100
                     (Dbottom) x (Dbottom) x CH

Example: Trees 16 feet tall but top 2 feet do not include much canopy, so that CH = 14. Central leader trees, distance from trunk to canopy = 5.5 feet at 6 feet above the ground, and 7 feet at the bottom of the canopy.

% Canopy within Deer Browse Zone

= 100 – 5.5 x 5.5 x (14 – 4) x 100
                     7 x 7 x 14

= 100 –  (30,250  /  686)

= 100 – 44  =  56%

STEP 2
    Calculate the Deer Damage Percentage on representative limbs.

    For each tree selected in step 1, assess deer damage as follows. Divide the tree into rough thirds and randomly select a limb (about 3/4 to 1 inch diameter) from each third. In addition, choose another limb from within each third that has no apparent browse damage.

    If deer damage is so extensive that no "unbrowsed" limbs exist, select the undamaged limbs from just above the browse line, or from an adjacent tree.

    For each of the 6 limbs (3 damaged, 3 undamaged), count the total number of fruit buds and the number of those fruit buds injured by deer feeding.

Example
Browsed Limbs
Limb #          Number of buds             Number of injured buds
1                             30                                        15
2                             55                                        37
3                             50                                        39
Totals                    135                                         91
% Damaged Buds = 91 / 135 = 67%

UnBrowsed Limbs
Limb #          Number of buds             Number of injured buds
1                             45                                          5
2                             45                                          8
3                             55                                          9
Totals                    145                                         22
% Damaged Buds = 22 / 145 = 15%

Calculate the Deer Damage Percentage by subtracting the % Damaged Buds on UnBrowsed limbs from the % Damaged Buds on Browsed limbs.

Example: Deer Damage Percentage  = 67% – 15%
                                                          = 52%

STEP 3
    Estimate the Deer Damage Factor for the tree as follows:

Deer Damage Factor =
(Deer Damage %   x   % Canopy within Deer Browse Zone) / 100

Example (using values from example above)
= (52%  x  56%)  /  100
= 2912 / 100 = 29%

In the final three steps, you calculate loss on a per acre basis.

STEP 4
    Find the average of the Deer Damage Factors calculated for all of the sample trees.  After harvest, estimate the Potential Crop without deer damage

    Potential Crop =                Actual Crop x 100                
                                       (100 – Average Deer Damage Factor)

STEP 5   
    Calculate the Crop Loss per Acre

Crop Loss per Acre = Potential Crop – Actual Crop

Example
     The Average Deer Damage Factor for the trees examined in the block was 40%. You pick 300 bushels per acre from the block.

Potential Crop = 300 x 100 / (100 – 40)
= 30,000 / 60
= 500 bushels per acre

Crop Loss per Acre = 500 – 300 = 200 bushels per acre

STEP 6
    Calculate the Dollar Loss per Acre

   
Dollar Loss per Acre = Crop Loss per Acre x Lost Returns per Bushel

Lost Returns per Bushel = Selling price per bushel minus expenses for picking, storing and marketing each additional bushel.

Example
Selling price $20.00 per bushel
Cost per bushel: picking $2;  storage $3; marketing $4
           (includes grading, cardboard, trucking, broker fee)
           Total costs = $9.00

Lost Returns per Bushel = $20 - $9 = $11

Dollar Loss per Acre = 200 bushels per acre  x  $11 per bushel
= $2200 per acre