Location: Vegetable Crops Research Unit
Title: When and how long to flood for insect control Authors
Submitted to: Cranberry Crop Management Newsletter
Publication Type: Trade Journal
Publication Acceptance Date: June 3, 2014
Publication Date: N/A
Technical Abstract: Flooding in late spring (late May or early July) can remove tremendous numbers of arthropods from cranberry beds. For over 100 years, the Wisconsin cranberry industry has used flooding as a way to suppress arthropod populations. One critical element of this strategy is the trade-off between lethality for insects and harm to the cranberry plant. One basic question underlying our flooding research, therefore, has been the following: How late can we push the flood timing to hit the caterpillars, and how long can we hold the water without hurting the plant? In collaboration with Wisconsin pest management consultants and growers, we set up a large-scale experiment in central Wisconsin in 2011. This work involved 23 pairs of flooded and unflooded beds (46 beds total, among 11 commercial growers), and we included not only arthropod metrics (Sparganothis fruitworm, cranberry fruitworm, and black-headed fireworm densities), but also plant metrics (chlorophyll, upright growth, flowers/upright, harvestable crop) and surface water metrics (temperature, dissolved oxygen, and pH). In parallel, we conducted a submergence tolerance study in a greenhouse setting, where we could concurrently manipulate the effects of water temperature (cool, warm regimes) and submergence duration (0, 48, and 96 hrs) on three different cranberry varieties (‘Stevens,’ ‘Ben Lear,’ and ‘GH1’). From our field data, we showed that springtime surface waters in Wisconsin were generally well-oxygenated and cool (8.2 ppm at flooding, and then 7.7 ppm as water drained; 64-65°F). As water temperature rose, dissolved oxygen (DO) declined. Altogether, our findings suggest that 30-40 hours of flooding in late spring do not affect the cranberry harvest, and the floods do help to suppress insect populations. Growers flooding for longer periods will want to watch dissolved oxygen levels in their floodwater, because over time, dissolved oxygen levels slowly decline.