SUMMARY OF CRANBERRY FRUITWORM COVER STUDY

CONDUCTED IN 2003 AND 2004 AT SPARROW FARMS IN PITTSTON, MAINE

Key Question: Are enough cranberries protected from cranberry fruitworm by using a polypropylene fabric row cover to justify the expense of the cover?

Quick Answer: It was worth it in 2003 (net gain of $1,619.98) but not in 2004 (net loss of $529.70).

Why the big difference? It all depends on the level of fruitworm pressure and on the total yield. At Sparrow Farms, the key factor was by far the difference in fruitworm levels between 2003 and 2004--very high in 2003 but very low in 2004 (see Table 1).

Estimates of Cranberry Fruitworm (CFW) damage at harvest time:

Uncovered Areas - Sept. 26th, 2003: 147 berries damaged out of 585 (25%)

Uncovered Areas - Sept. 25th, 2004: 22 berries damaged out of 1262 (1.7%)

Table 1. Cost versus Benefit (Sparrow Farms).

Percent Loss to CFW / Percent of Crop
Saved by Cover / Number of
Barrels Saved / Value of Barrels Saved
(Organic Fresh-Pick)
Year / With Cover / No Cover
2003 / 12.40% / 25% / 12.6% / 7.90 / $2,369.98 / $2,764.98
2004 / 0% / 1.7% / 1.7% / 0.90 / $270.30 / $315.35
Price of berries per pound: / $3.00 / $3.50
Cost of
Cover / Acre
Year / Net Difference
2003 / $750.00 / $1,619.98 / $2,014.98
2004 / $800.00 / -$529.70 / -$484.65
Price of berries per pound: / $3.00 / $3.50

Table 2. Break-even Points. NOTE: The percentages here would be cut in half if one were to reuse the same cover for an additional year (as has been done at Sparrow Farms).

% Crop Loss to CFW (if no cover used) Needed To Pay for using the Cover at Sparrow Farms
Year
2003 / 4.0% / 3.4% / 3.0%
2004 / 5.0% / 4.3% / 3.8%
At $3.00 per lb. / At $3.50 per lb. / At $4.00 per lb.

Key Question for All Growers: Assuming 0% loss to Cranberry Fruitworm using the cover, how much crop would otherwise need to be lost in order for someone to recover the cost of the cover?

Table 3. Cost versus Benefit (All growers).

Yield
Bls / Ac. / % Crop Loss to CFW (if no cover used) Needed in Order to Pay for the $800 / acre Fabric Cover (i.e. Break-Even Point) at Various Berry Prices
50 / 40% / 29.1% / 8% / 5.3% / 4%
100 / 20% / 14.5% / 4% / 2.7% / 2%
150 / 15% / 10.9% / 3% / 1.8% / 1.5%
200 / 10% / 7.3% / 2% / 1.3% / 1%
$0.40 per lb. / $0.55 per lb. / $2.00 per lb. / $3.00 per lb. / $4.00 per lb.

SARE Farmer/Grower study. Report prepared by Charles Amrstrong, Cranberry Professional, University of Maine Cooperative Extension.