in cooperation with Oregon State University Bee Lab
An Evaluation of Pollinator Management as Applied in the Commercial
Production of Cranberries - 1987
Final Report: October 1, 1987
Submitted to: The Oregon Cranberry Growers Association
c/o Coos County Extension Office
290 N. Central Blvd.
Coquille, Oregon 97423
Submitted by: Michael Burgett, Assoc. Professor Department of Entomology, OSU and Arthur Poole, Extension Agent-Cranberries Horticultural Crop Management Coos County Extension Service
Introduction:
In 1986, the Oregon Cranberry Growers Association identified honey bee pollination as an area of potential improvement in the overall management scheme for the commercial production of cranberries. Late in the same year a proposal addressing pollinator management was submitted by one of us (MB) to the Cranberry Growers Association. After review, this proposal was approved and funded for 1987. The proposal had two primary objectives:
1) To quantitatively assess honey bee colony strength relative to standards set forth by the Oregon Department of Agriculture (ODA).
2) To assess grower and beekeeper management practices that would improve pollinator effectiveness.
In early June, 1987, the authors, accompanied by two technical assistants, spent four days inspecting rental honey bee colonies that had been placed adjacent to bogs as supplemental pollinators. Colony strength assessments were done according to standardized methods outlined in Burgett and Burikam (1985). Average colony evaluations were then related to the ODA grading system that is found in appendix I of this report. Concurrent with colony assessments, additional management practices on the part of both beekeepers and cranberry growers were examined during both the survey period and in post-survey farm visits. During the major survey period (June 4-7) cranberries were in 20 to 80% bloom depending upon variety, with hybrids in a more advanced stage of bloom. Weather conditions during the survey were less than ideal for honey bee foraging. However, this contributed to more accurate estimates of adult bee populations. A total of 8 cooperating beekeepers participated in the study. These eight individuals were responsible for in excess of 95% of all colonies rented for cranberry pollination in 1987. For statistical purposes, either 10 or 12 colonies were examined for each beekeeper and most often this was done at two separate farms. Bogs owned by 15 growers were visited. A total of 90 honey bee colonies were examined in detail. During the survey an additional five colonies were discovered to be infected with the bacterial disease American foulbrood and colony examinations were immediately discontinued due to the hazard of equipment contamination.
Results:
Colony Density: From a sample of 452 acres of bearing cranberries the average colony density per acre was 1.6. Published recommendations for colony density (McGregor 1976) range from a low of one colony per five acres to a high of ten colonies per acre. For reasons of competing bloom and often marginal weather conditions for honey bee flight in Coos and Curry Counties during cranberry bloom, the authors recommend a density of 1.5 to 2 colonies/acre with a preference towards the higher end of the range.
Colony Placement: Colonies were observed to be most often positioned in windbreaks along bog edges. This is a wise and recommended practice. Due to solid planting systems and frequent wetting conditions, colonies cannot be placed in bogs. The relatively small size of individual bogs and the clustering of bogs permits the efficient placement of colonies next to natural windbreaks while at the same time having the colonies close enough to the bogs to affect pollination. Nearly all colonies observed were found to have early and full exposure to sunlight. This is another encouraged practice as it allows the foragers to leave the colonies as soon as the flight requirements of temperature and light intensity are met.
Competitive bloom: Cranberries, Vaccinium macrocarpon, have a comparatively long flowering period which, especially during the early stage of bloom, is concurrent with a number of native (wild) nectar and pollen sources available to honey bees. It has been frequently observed in eastern cranberry growing regions that honey bees forage on cranberries primarily for pollen as little nectar is produced. In recognition of this McGregor (1976) stated: "Because cranberries are not highly attractive to honey bees, the bee population should overflood or saturate the competing plants so the bees will visit the cranberry flowers." We fully concur with McGregor's statement.
Timing: Rental hives should be moved adjacent to the bogs no earlier than 10% bloom and no later than 25-30% bloom. As each year's bloom phenology varies it is difficult to establish calendar recommendations. 1987 was an unusual year in the earliness of bloom which also exacerbated the problem of competing bloom.
Colony strength: Appendix II reviews the average colony strength for each cooperating beekeeper and the average colony strength from all sampled colonies. The average colony did not meet the Grade A standard (1000 in2 of live brood sand 24,000 adult workers). By allowing for a 10% grading tolerance r the average colony did meet the Grade B standard (750 in of live brood and 18,000 workers). In reviewing individual colony data it is seen that 28% of the colonies (25 of 90) were at Grade A and an additional 18% of the colonies (16 of 90) were at Grade B. This means that 46% of the examined colonies meet either Grade A or B; conversely, 54% of the colonies failed to meet grade.
The most common failure in meeting grade was the lack of sufficient adult bees. The majority of colonies did possess enough brood (eggs, larvae and pupae) as did the average colony, however a colony must have both sufficient brood and adults in order to meet grade. Of the eight surveyed beekeepers only one had a colony average of Grade A, with an additional three beekeepers averaging Grade B.
Diseases: It has been a frequent observation by beekeepers who pollinate cranberries, both in the eastern and western cranberry growing regions, that certain bacterial infections are commonly observed in honey bee colonies during the cranberry bloom period. The most routinely observed disease has been European foulbrood, a pathogenic condition which will weaken but not kill a colony. Contrary to these observations, we found no European foulbrood, but did encounter five colonies infected with the more serious American foulbrood, which will ultimately kill a colony if not treated. The fungal disease chalkbrood was found in the majority of colonies examined. Chalkbrood, a disease for which there is no recommended or even known medicament, is presently in an epidemic state throughout the U.S. and its presence in a colony is largely out of any individual beekeeper's control. Like European foulbrood, chalkbrood will not kill a colony but it does reduce a colony's effectiveness by elevating brood mortality.
Queenless colonies, while not a disease, are greatly reduced in value as pollination units due to the lack or reduction in the amount of brood in colonies so affected. Twenty-one percent of the sampled colonies were queenless. The majority of queenless colonies we observed and recorded were not caused by colonies undergoing a swarming phase. Swarming colonies, while not necessarily possessing a laying queen, will have either pupal or virgin queens present. The queenless colonies we encountered were void of any queen state.
Recommendations:
The ultimate question in the grower's mind regarding pollination is; are there sufficient bees present to optimize fruit set? For 1987 we would conclude, based on colony density (1.6/a) and the average colony strength, that the honey bee population for the average bog was somewhat less than adequate. We caution however, that this assumption is based on observations for only a single growing season for what we conceive as the average bog in the Bandon cranberry area.
To insure adequate pollination service in future years we would make the following recommendations/observations:
1. Use of a pollination contract between individual growers and beekeepers. The Cranberry Growers Association should give some thought to the design of a "standard" contract for use by member growers. As an assist to this recommendation, interested parties should consult Extension Bulletin PNW 245, Evaluating Honey Bee Colonies for Pollination (Burgett et al. 1984), which outlines the contents of a pollination contract.
2. Increase the number of colonies rented. The observed density of 1.6 hives/a is at the low end of the recommended density range. An average of 2.0+ colonies/a is a suggested target. Associated with this should be a grower effort towards uniformity of density, meaning adjacent bogs owned by separate growers should possess similar colony densities. 3. Pollination economics. It was interesting to observe that an informal 'standard' pollination fee was in existence, i.e. $26.50/colony. We discovered only a few growers who were paying a fee different than the 'standard.' Therefore, for 1987 the average pollination cost per acre, based on the observed average colony density of 1.6 colonies/a, was $42.40. Published reports show a 1986 average yield/a of 97 bbl at $53.00/bbl. This is a gross return/a of $5141. The pollination cost is therefore, 8/lOth of one percent relative to gross return. By increasing the colony density to 2/a, the average grower's pollination cost would increase by 2/10ths of one percent, based on statistics provided by the OSU Extension Service. V
Acknowledgements:
We wish to thank all cooperating beekeepers and growers who participated in this study and the Oregon Cranberry Growers Association for funding. It is our hope that this report will result in an increased understanding and appreciation of the value of honey bees as supplemental pollinators and ultimately their more efficient use in commercial cranberry production.
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Literature Cited:
Burgett, M. and I. Burikam. 1985. Number of adult honey bees (hymenoptera: apidae) occupying a comb: a standard for estimating colony populations. J. Econ. Entomol. 7S: 1154-56.
Burgett, M., Fisher, G.C., Mayer, D. and C.A. Johansen. 1985. Evaluating honey bee colonies for pollination: a guide for growers and beekeepers. Ext. Serv. PNW 245. 8 pp.
McGregor, S.E. 1976. Insect pollination of cultivated crop plants. USDA Agri. Handbk. No. 496. 411 pp.
Miles, S. 1986. Oregon county and state agricultural estimates. Spec. Rep. 76}. OSU Ext. Serv. 13 pp.
Williamson, P., Marousek, D. and G. Miller. 1987. Oregon Crop-Weather. Oregon Agricultural Statistics Service. 87(10): 2. Appendix I
Oregon Department of Agriculture colony strength regulations. [From Oregon Administrative Rules, Chapter 603, Section 55-005, filed with the Secretary of State August 17, 1960, as Administrative Order AD 643] 55-005-Bees. (1) As used in this section:
(a) European foulbrood shall be deemed serious if 20 or more larvae are found dead from this disease and more than 20% of the cells in the capped brood area are vacant.
(b) A queen shall be deemed a normal laying queen if her eggs that are in the worker cells are producing worker bees as indicated by the brood present.
(2) Oregon Standard (or Grade A) Field colony of bees for pollination shall be one that meets the following requirements:
(a) Free from American foulbrood and not seriously infected with European foulbrood or other bee disease.
(b) 3,000 square inches of comb, 1000 square inches of which shall be occupied by live brood.
(c) Bees to cover well all brood. There shall be enough bees to cover well 10 standard Hoffman frames of comb or their equivalent.
(d) 10 pounds of honey or its equivalent of suitable bee food other than pollen or pollen substitute.
(e) A normal laying queen present.
(3) Oregon B grade Field colony of bees for field crop pollination shall be one that fails to meet the requirements of a standard field colony on amount of bees and brood by not over 25% but does meet all other requirements of a standard field colony.
To allow for variations incident to proper grading, a tolerance of 10% shall be allowed on all defects other than diseases and queens.
[For a more complete explanation of ODA colony grading regulations interested parties should consult the Cooperative Extension Publication PNW 245, Evaluating Honey Bee Colonies for Pollination.]
| Ave. In.2 brood | Ave. No. adults | Grade A colonies | Grade B colonies | Queenless colonies | |
| Beekeeper A | 1,429 | 26,375 | 9 of 10 | 0 of 10 | 0 of 12 |
| Beekeeper B | 1,170 | 20,700 | 4 of 12 | 2 of 12 | 2 of 12 |
| Beekeeper C | 960 | 18,700 | 3 of 12 | 5 of 12 | 1 of 12 |
| Beekeeper D | 840 | 20,700 | 4 of 12 | 2 of 12 | 4 of 12 |
| Beekeeper E | 960 | 17,700 | 1 of 10 | 2 of 10 | 2 of 10 |
| Beekeeper F | 1,073 | 17,300 | 2 of 12 | 4 of 12 | 4 of 12 |
| Beekeeper G | 943 | 12,740 | 1 of 12 | 1 of 12 | 2 of 12 |
| Beekeeper H | 523 | 10,300 | 1 of 10 | 0 of 10 | 4 of 10 |
| Average Colony | 990 | 18,000 | 25 of 90 (28%) | 16 of 90 (18%) | 19 of 90 (21%) |
ODA Grade A 1,000 24,000
ODA Grade B 750 18,000
Standard 0
CODA standards lists 10 Hoffman combs covered with adult bees. One Hoffman comb covered with bees = 2,400 adults.