Frost Protection: Know the tolerance levels for your variety or varieties, and monitor your bud stage throughout the month (use the bud stage that the majority of your vines are showing).
Mid to Late April: Pre-emergence herbicides need to be applied before cranberry vines break dormancy. For a list of herbicides, and individual target weeds, check the weeds portion of the Maine Cranberry Pest Management Guide.
Late April: Late-Water Flood (MS Word) | Late-Water Flood (pdf). Do not apply this flood if the buds have broken dormancy, or if the winter has been severely cold and long, oxygen deficiency conditions are suspected, or if the bed has been sanded since the preceding fall. The flood provides very good control of fruit rot fungi, boosts keeping quality, and kills overwintering Cranberry Fruitworm and may eliminate the need for sprays for this insect during the Late-water year (Expect 90% or more Cranberry Fruitworm control if the flood is held for four weeks, 40-50% control if less than four weeks); virtually wipes out Southern Red Mite infestations and may suppress False Armyworm and Gypsy Moth larval populations; can delay the development of weeds (suppresses growth of some perennials, most notably brambles; the flood does not control dodder)
