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IPM Message for Cranberry Growers: Jul 25, 2016

July 25, 2016

We had our first report of early rot late last week (July 22).  This is caused by the fungus, Phyllosticta.  Remember that resistance development to Abound, Indar, and Proline is a real and serious threat.  Applications of these fungicides should be made PRE infection rather than POST infection (now).  For RM purposes, it is best to use multi-site contact fungicides, like chlorothalonil or mancozeb, later in the bloom period (fruit set).

You should confirm any restrictions that your handler might have concerning pesticide use at this point in the season.  Ocean Spray growers selling export cannot use chlorothalonil or Evito after July 25; Sevin and Belay cannot be used after Aug 1.

To clarify the “150” number for assessing increased risk of injury (degrees F + humidity) when applying herbicides and adjuvants (mentioned last message), this is borrowed from weed scientists working in agronomic and row crops.  It is simply a guideline to help you gauge when injury might be more likely. A grower asked me what temperature should they use, shelter or vine canopy? My best response would be to use vine canopy as that is where the herbicide and adjuvant would be applied. 

Our July 22 newsletter (see link on home page) has extensive discussions on managing cranberries during hot conditions.  Stem gall has also been seen on several sites in MA.  Erika has photos and descriptions in the newsletter.  It is a sporadic disease but you should familiarize yourself with the symptoms; no chemical control is recommended.  Efforts to reduce unnecessary damage during harvest and providing good frost protection are generally good enough in most years. Erika also requests that if you see signs of possible virus symptoms, you can send samples to her and she can get them processed free of charge via grant monies; this is the last year. See the newsletter for sample collection information and/or call Erika at ext. 18.