May (Maine Cranberry Management Calendar)

  • After terminal bud has broken dormancy & begun to swell or grow: The approximate window for spraying for Upright Dieback control is April 30 – May 20. For Washington County growers, the target window is likely a bit later (May 6 – 26). But, exact timing depends on whether the variety is early or late-season. Remember, too, that if a chlorothalonil application is used at this time, that leaves only two more available that you can use for fruit rot control. For a list of available fungicides you can use, and details about the disease, consult the Maine Cranberry Pest Management Guide. Note: Bravo® does not control upright dieback if applied later than early bloom—by this time the fungus has apparently invaded shoots and is out of reach of the material. Fungicides will not cure upright dieback but will prevent the spread of the infection.
  • Callisto® for weeds just starting to emerge (but avoid using it year after year so as not to encourage resistance): (best if <5″ tall, yet growing  actively) (~From May to 45 days before harvest or flooding, and not during bloom) Callisto® is reportedly an extremely good choice for weed control, having both pre-emergence activity as well as post-emergence activity (especially when weeds are <5″ tall), and you are encouraged to wait for that stage.  If you apply too early, some weeds with vast root systems–such as cinquefoil–can quickly recover. Thus, for cinquefoil, wait until the first flush of new growth has taken place.  The maximum application rate is 8 oz/acre/application; no more than two apps. per season, and split apps. need to be at least 14 days apart. Callisto® is effective against a large number of different weeds (will control most all annual broadleaf weeds if under 5″ tall), but plan on several years of treatment in order to achieve permanent control of many perennial weeds, especially yellow loosestrife/swamp candles. Birdsfoot trefoil and other Lotus members are very sensitive to Callisto® (but more difficult to control if they are completely covering over the cranberry canopy). Cranberry vines are highly tolerant of Callisto® – they can readily metabolize its active ingredient (mesotrione).
  • ~May 14 – May 31(vegetative buds elongated 1/2″ and flowering buds at bud break stage): Cranberry tipworm begins! (Flies appear first, followed by eggs and larvae once new tips begin to grow) Overwintering pupae will be hatching out into flies (the length of this period is a bit uncertain and probably varies from year to year).  Individual flies only live for about 3 days (5 at most), so right out of the gate they are busy mating and laying eggs on the terminal leaves of uprights (mostly on the tips of brand new uprights sprouting up from the runners).  The more dormant the upright, the less likely its chances of being chosen for egg deposition by the female tipworm fly. Conventional wisdom is to treat at the peak of egg hatch, or slightly before that period in the case of any material that provides a good residual or has systemic activity.  The window for either of these timings is somewhat narrow. See also: Degree Day Model
  • ~May 20th – Early June (tip elongation):
    • False Armyworm larvae begin (If no Late Water flood was used). These cutworms have been consistently found in significant numbers on Maine cranberry beds annually. The larvae feed on leaves, stems and buds (basically consume entire uprights), and get quite big when mature (2” long), at which point (late June into July) they feed almost exclusively at night. Sweepnet First Dates (Average First Date = May 24th): 6/6/97, 5/28/98, 5/28/99, 5/24/00, 5/31/01, 5/13/02, 5/24/05, 5/25/07, 5/14/08, 5/14/09
    • 1st-generation Blackheaded fireworm larvae begin! Spend some time visually scanning for upright tips with terminal leaves that have been webbed tightly together!  Break off any tip of that sort, and carefully tease apart the terminal leaves.  If a small larva suddenly squirms out, wriggling backwards and possibly right across your hand and down to the ground (often attached to a strand of silk)…and if this happens before you’ve even blinked, then you’ve probably encountered a fireworm larva. You should then sweep to see if you pick up any in your net.  They do not get picked up in sweeps very easily, so if you average even just one larva per 25 sweeps, you may well be justified in taking action (depending on your history with this pest, your expected crop value, etc.). View the Maine Cranberry Pest Management Guide for the most current recommended Action Threshold (AT) to consider using (traditional AT is 1), and for a list of control materials.  Infestations of 2nd-generation larvae are far more dangerous, because their numbers are much higher, especially, of course, if any 1st-generation populations are left uncontrolled.  Infestations of both generations are usually patchy, at least at first, and larvae tend to be more numerous along edges. Spot-treatment is desirable in such cases. Sweepnet-captured ‘First Dates’ for 1st-generation larvae: 6/12/06, 5/25/07, 5/14/08, 5/14/09, 5/16/13, 5/20/14, 5/27/17, 5/21/18 (Average of these = May 22nd); See also the Pest Report each year for news of Maine’s first detection of 1st-generation fireworm larvae.

Disclaimer: Pesticide registration status is subject to change and varies from state to state; therefore the author and the University of Maine Cooperative Extension cannot assume liability for any pesticide recommendations. It is the responsibility of the pesticide applicator to verify the registration status of any pesticide before applying it. The label is the law! Always read and follow the label when applying pesticides. Use of product names does not imply endorsement.