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IPM Message for Cranberry Growers: May 7, 2021

May 7, 2021

There have been reports from early scouting of very small larvae; they are likely green spanworm or winter moth. It is very hard to tell them apart when they are so small.  We have also had reports of weevil, but mostly on edges near the woods.  We would not recommend spraying right now anyway for high weevil numbers.

Sprays for upright dieback should be made after the bud has broken dormancy (at bud break and/or early bud expansion) and has begun new growth. This is usually somewhere around mid-May but will vary by location and by variety.  Be sure that the fungicide you are using (chlorothalonil or copper) is labeled for URD use.  Not all fungicides (especially many of the generics) are labeled for URD. If the Phytophthora diagnosis is confirmed and bog drainage is improved, the first application could be made between April 25 and May 15. The spring application could slow down the infection. The ideal time for Phytophthora fungicide applications is when soil temperatures are conducive for root development and pathogen multiplication (May, June, July and August). Be sure you have a diagnosis for Phytophthora and improve your drainage before spending money on fungicides.

We received about 1 inch of rain per week in the past 2 weeks for a total year rainfall of 16.6 inches.  Highlights from the frost report.

• On May 6th, Elongation stage bud tolerance for Early Black and Howes is 27°F; for Ben Lear and Stevens it is 29.5°F. Cabbage head stage tolerance for Stevens is 27°F.

Note: starting with cabbage head stage, development continues even when visual stages appear not to change. Each stage, starting with cabbage head, only lasts 5-7 days!

• The Dee model predicts bud swell at 150 GDD (degree days). On April 28th, East Wareham reached that benchmark. Bud swell was observed in the field on April 26-27th.

The Dee model predicts cabbage head at 200 GDD; East Wareham reached that benchmark on May 3rd. We first observed this stage on April 30th.

We will be hosting a lunchtime bogside workshop this coming Wednesday May 12, from noon-1 pm.  The zoom link is: