Cooperative Extension: Maine Wild Blueberries

Monilinia infections from May 3 to May 5th 2022

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Midcoast

Monilinia cups are still present in the fields as of Monday May 2nd.  Some cups were starting to dry up but they were still active cups present.  Plants are still susceptible in all of the fields.  In Waldoboro, many flowers were close to opening, and there were some open flowers.

Downeast

Monilinia cups were present in all of the fields checked on Tuesday.  Plants are at susceptible stages.

Monilinia infection

There were conditions for Monilinia infection from Tuesday May 3rd through to early morning on Thursday May 5th in most fields with weather stations.  Two monitored fields, Crawford and Eastbrook, had too cold temperatures with not long enough rain to have infection starting on Tuesday; instead both fields had Monilinia infection periods that started on Wednesday May 4th.

I expect these will be the last Monilinia infections this season considering the warm and dry weather forecast for the next week.  I suspect we will start seeing symptoms of past Monilinia infections (from prior weeks) starting next week.  If there are no mummy berry cups in your field, applying fungicides after symptoms occur is not recommended.  A fungicide application this close to bloom may disrupt bee pollination, since bees do not like the “smell” of some fungicides.  Bees transport the spores from tissue killed by mummy berry disease to healthy flowers, and those spores infecting the developing fruit to produce mummy berries. Usually by the time you see symptoms on the plants, the bees have already started transferring the spores to flowers and may have been doing so for days. A fungicide application right before bloom will only decrease flower infection and the number of mummy berries produced but probably not enough to typically warrant the expense of the fungicide.

If you have applied fungicide after April 26th (7 days) or April 23rd (10 days), your plants would have been protected during this infection period.  If you have not applied fungicide, you have approximately 72 hours after the start of the infection period to apply propiconazole or fenbuconazole to possibly decrease infection.

Botrytis blossom blight

Now is the time to look for Botrytis blossom blight on early developing clones.  Conditions, long period of leaf wetness with warmer temperatures, that could have caused Botrytis infection on T5 (almost open) or open flowers did occur in Waldoboro, Hope, Liberty, Ellsworth, Eastbrook and Steuben this week.  You will only get infection if the fungus was already present in your fields.  Three to seven days after a possible infection is when you should start looking for Botrytis disease.