Why Are Wisconsin Cranberry Yields Declining?

WHY ARE WISCONSIN CRANBERRY YIELDS

DECLINING?

Bill Bland

Department of Soil Science

University of Wisconsin-Madison

As with most crops, yields of cranberry increased dramatically during much

of this century. Wisconsin cranberry acreage yielded about 20 bbls/acre through

the first 30 years of the century, after which a steady increase began. Between

1960 and the early 198Os, yields increased nearly 3 bbls/acre each year (Fig. 1).

Following the record statewide yield average in 1982, however, the per acre yield of

cranberry in Wisconsin appears to be declining, nearly 20% below early 1980 yields

and 50 bbls/acre below that expected if the 1960- 1980 rate of increase had

continued. While all crop yields fluctuate from year-to-year and IO-year periods of

little increase are in the Wisconsin cranberry record, the decrease that began in

the early 1980s appears to be more than just bad luck. With the accumulated

value of these missing berries in excess of $120 million, an explanation is needed.

The cause may be due to circumstances beyond our control, or it may be due to

factors that improved management and directed research can overcome. A

number of possible reasons for the decrease are being considered by a team of

UW-Madison researchers. In this paper, I investigate the evidence that the yield

decline is more than just chance, and test a number of candidate causes.

Cranberry Technology

One possible explanation is that the new technologies that propelled the

yield increase from the 1930s to the 1980s are no longer being introduced, or are

wearing-out. By technology, I mean the application of knowledge, be it through

design and use of machines and chemicals, or better understanding of how to best

manage both pests and the crop. Technologies such as chemical fertilizers,

overhead irrigation, water harvesting, and chemical pest control provided great

advantages and yield improvements. Are we out of new tricks? Do technologies

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