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IPM Message for Cranberry Growers: May 14, 2021

May 14, 2021

As of May 12, we had 24 possible frost nights; 8 were called as dangerous and 7 as possible.  9 nights had no frost predicted. The recent string of frost nights may contribute to waterlogged areas on the bog, so improving (managing) drainage is very important. Proper soil drainage results in optimal aeration of roots, healthy vines and improved fertilizer use efficacy. Poor drainage prevents rapid drying, weakens vines, and makes the plants susceptible to the infections by fungal pathogens (Phytophthora root rot and fruit rot). Poorly aerated root zones limit the plants ability to acquire nutrients from the soil.

If your bog had >5% upright dieback severity and you choose to spray chlorothalonil or copper fungicides, sprays should be made after the bud has broken dormancy (at bud break and/or early bud expansion) and has begun new growth. Most of the varieties are at or around that stage now. Please monitor the bud on your bog and make a timely decision.

Most people are finding low numbers of weevil and low winter moth/green span. Only one report of tiny spag and tiny black-headed fireworm. We did hear of a few reports of high weevil on edges (20+). Weevil will be more active on warm sunny days, which look to be in our future next week.  This also means black-headed fireworm and spanworms will be more active.  Intrepid may be a good choice sooner and maybe wait on applying Actara for 1 week or so.

Just to clarify from last week’s message about holding off for treating weevil; I was referring to low numbers as a time not to treat. However, if you have "treatable" weevil, you should treat with Actara . (That is, if you have a 20 count, or whole piece averaging 6 or more, then that would be a treatable population!!)

For those of you who held late water (LW), management after late water is as important as the practice itself to reap the benefits of this cultural practice.

Irrigation: For at least 2 weeks after the LW flood is withdrawn, there should be no need to irrigate (unless protecting for frost). We recommend that you schedule irrigation based on soil moisture status determined by sensors or tensiometers.

Frost protection: After LW flood, buds are sensitive to frost injury. Frost management after the LW should be based on the actual duration of the flood, rather than the appearance of the buds.

1-week early spring flood: No impact on frost tolerance. Protect the buds based on appearance.

>1 - 2 weeks LW flood: Protect the buds for 27˚F

> 2 weeks LW flood: Protect the buds for 30˚F

Fertilizer use: LW bogs respond readily to fertilizer. Nitrogen (N) dose should be reduced to avoid overgrowth. However, do not decrease fertilizer N by more than 40%, a rate that would adversely impact the following season’s crop. The best tactic is to add no fertilizer for at least 2 weeks after the flood withdrawal and then time your applications by the plant’s development. No fertilizer should be needed until bloom.

< 3 weeks flood: standard fertilizer regime

> 3 weeks flood: Reduce N dose (30-40%) by eliminating the spring application.

Herbicide usage: Casoron and QuinStar may be applied after the LW flood is withdrawn for dodder management. After LW, low rates of Casoron (<40 lb/acre) are recommended. QuinStar could offer management of dodder, yellow loosestrife (YLS) and other broadleaf weeds. Up to two applications of QuinStar can be applied at 30-day interval at 8.4 oz/acre. No other preemergence herbicides are recommended after LW. POST herbicides can be applied when weeds have emerged, according to the label.