Integrated Management of Cranberry Insect, Weed - Disease Pests Using Fall - Spring Floods

Integrated Management of Cranberry Insect, Weed - Disease Pests Using Fall - Spring Floods

Summary

Overview
Post-harvest floods on cranberry beds have been shown to eliminate cranberry fruitworm in the overwintering stage, or hibernacula, and to suppress dewberry (Rubus sp.) growth by about 30 percent as compared with unflooded beds. A three-week flood appears sufficient to control fruitworm, but at least four weeks are required for effect on dewberry. To date, no adverse effect on yield has been found, but reduced fruit set in the year following the flood bears further study. A fall flood followed by a spring flood reduced yield with no additional pest control benefit. Shortened spring floods of about two-and-a-half weeks were significantly less effective than four-week floods in suppressing cranberry fruitworm.

Objectives
The overall objective of this project is to examine the use of flooding—four-week post-harvest; two-to-three week spring; short post-harvest—for the integrated control of cranberry weed, insect, and disease pests, thus extending our current knowledge of the impact of flooding on certain key pests and developing a strategy for reduced pesticide management that minimizes adverse cranberry crop and plant impacts. Preliminary observations have shown that post-harvest floods have less impact than spring floods on yield while seeming to offer at least some control of pests.

Methods
This project is third stage IPM, integrating harvest methods with management of multiple pests. Specifically we examine the effects of three-to-four week post-harvest floods, short post-harvest sanitation floods, or spring floods (short-term or combined with fall floods) on cranberry fruitworm (CFW), grub species, southern red mite, Rubus sp. weeds, fruit rot, and Phytophthora root rot. As any management for cultural control of pests must not only control the pests but also have no adverse effect on crop productivity, we also examine effects on cranberry growth and yield. Study sites are paired with unflooded control bogs.

Results
Five pairs of fall-flood sites were studied in 1998 and1999. A three-week flood was sufficient to control CFW while a longer flood may be required for dewberry control.

Flood length CFW mortality Change in dewberry crowns
4 weeks 100% (80% in control) -27% (+3% in control)
4 weeks 100% (80% in control) -31% (+3% in control)
3 weeks 100% (88% in control) +7% (-3% in control)
3 weeks 100% -41%
3 weeks 100% +2% (-35% in control)

An additional flood in the spring, after a fall flood, did not afford additional control of dewberry and resulted in crop reduction compared to the control bog and the fall-flood-only bog.

Four pairs of short spring flood sites were studied for effect on CFW mortality. At two sites, comparison to a four-week flood was made. Short floods improved CFW mortality compared to unflooded sites, but the traditional four-week flood afforded much better control (below). Based on these data, a short flood would not be a recommended practice for CFW control.

Site Flood length CFW mortality
1 2.5 weeks 50% (28% in control)
2 2.5 weeks 45% (13% in control)
3 2.5 weeks 40% (34% in control)
4 weeks 98% (20% in control)
4 3 weeks 41% (37% in control)
4 weeks 94% (71% in control)

To date, the effects of fall floods on cranberry growth and yield have been studied at two paired sites, comparing pre- and post-flood years for length and fruit set, and comparing to previous four-year average yield. While yield was lower on the flood bed compared to the control bed at Site 1, yield was greater than the previous four-year average (pre) for that bed, indicating no substantial negative yield effect. However, the decline in fruit set in the post-flood year bears investigation.

Site Yield (bbl/A) Upright length (mm) Percent fruit set
Pre Post Pre Post Pre Post
1 (Flood) 143 161 64 67 42.3 32.5
1 (control) 182 231 79 71 44.7 45.7
2 (Flood) 111 79 82 62 50.1 37.7
2 (control) 113 75 57 78 65.7 56.9

Impacts and Potential Contributions
By establishing a team of growers, researchers, industry, and extension professionals for this project, we hope to encourage wide adoption of the results. Flooding for these pests has the potential to reduce pesticide use and reduce the need for fumigating with harsh chemicals in order to eliminate dewberry prior to replanting the beds. Our outreach plan for this project will be targeted primarily at cranberry growers, industry representatives, and IPM providers. Grower participants in this project are well respected members of the cranberry growing community in Massachusetts and will, no doubt, be excellent distributors of positive project outcomes to their peers.

Reported November 2000

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