Fairy Ring Impact and Management on Cranberry Beds in New Jersey

item Oudemans, Peter - RUTGERS UNIVERSITY
item Polashock, James

Submitted to: North American Cranberry Research and Extension Workers Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: September 16, 2005
Publication Date: October 24, 2005
Citation: Oudemans, P., Polashock, J.J. 2005. Fairy Ring Impact and Management on Cranberry Beds in New Jersey. North American Cranberry Research and Extension Workers Annual Meeting.

Technical Abstract: Fairy ring is a disease found on cranberries in the eastern growing regions, especially New Jersey and Massachusetts. Recommended treatments for this disease include application of Ferbam (carbamate) at a rate of 0.43kg/m2 which works out to approximately 4305kg/ha. Although treatments are typically made to the symptomatic areas (which is generally much less than the area under cultivation), this recommendation represents an extreme expense. In our research, we were interested in assessing the yield effects of fairy ring and developing a model for estimating impact. The first part of the study included development of a GIS representing the area affected by fairy ring over a course of 15 years. This data was collected from georeferenced aerial imagery and later from GPS files created by walking the perimeter of fairy rings. Yield effects were determined by sampling berries from inside and outside of the rings. Fruit rot estimates were also made at harvest. During the growing season, flowering phenology was measured. Ring growth rates were determined from the imagery and GPS data within the GIS and were found to range from 0.5-0.75m in radius per year. However, as rings grew, they often merged with neighboring rings making accurate measurements difficult. Yields within rings were generally 50%-70% less than unaffected areas of the bed. These estimates included the effects of fruit rot which ranged from 20%-70%. Fruit rot levels were typically higher within the rings than outside. This was presumably due to earlier flower development within the rings leading to fruit development prior to fungicide applications for fruit rot. One observation that has been made regarding Fairy Ring is an increase in genetic heterogeneity of the vines in affected beds. This is likely due to increased fruit rot and subsequent ¿seeding¿ of the bed when the fruit decompose. To test this, DNA fingerprinting methodology was used to compare genetic diversity of the cranberry vines inside and outside of the rings. These results suggested that genetic diversity within the fairy ring affected areas averaged three times higher than unaffected areas within the same beds. In addition, weed pressure was measured and we found that weeds were more likely to establish within the damaged areas of the bed. Although the crop loss does not, in general, justify repeated use of Ferbam at the labeled rate, this disease does cause some rather cryptic effects that can jeopardize the crop by providing a foothold for intrusive weed species and possibly increasing the genetic diversity and promoting rogue cranberry genotypes that can reduce crop yield once established.

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