Cooperative Extension: Maine Wild Blueberries

5.21.14 Mummy Berry Infection and Botrytis Blossom Blight

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Knox, Lincoln and Waldo Counties

Botrytis Blossom Blight

This is the time of year to scout for Botrytis blossom blight on early blooming blueberry clones.  Look at dead open flowers, and any dead or dying tissue (leaves or flowers) you see on weeds near or in your fields.  The symptoms are dead, open, flowers with black hairs sticking out of them. You will probably need a magnifying glass or hand lens to see the hairs. Your flowers may also be killed by mummy berry disease, which will not have the black hairs sticking out of the dead tissue. If you do have Botrytis in your field and are getting a lot of bloom, this wet weather over the next week may cause infections by this fungus.  It is only worthwhile to apply fungicides for Botrytis blossom blight if you are sure you have this disease in your field.  If you do not have this fungus in your field, no matter how much wet weather you get during bloom you will not get Botrytis disease.  Be careful to protect pollinators if you do have to spray for this disease, spray when pollinators are not in the field.

Hancock and Washington Counties

Mummy Berry Disease

There were mature spore-producing cups found in a few plots around the barrens on Tuesday.  Most locations the cups were drying up. I expect there are still a few cups around in the barrens and they will be finishing up this week.  If you have a later or wetter field there is a chance you may have had infection periods in the past few days. Infection periods occurred overnight on Monday, May 19 and Tuesday, May 20 (please see chart below). Wet weather is expected to continue the end of this week.

Infection Periods and Fungicide Applications

Your fungicide application should protect your plants for about seven to ten days.  With heavy rainfall, there may be a bit shorter protection than ten days. With the infection periods in the last two days, you have until about three days from the start of the infection to treat your plants to protect them.

If you would be applying a second application of propiconazole, it would be a good idea to switch to a different fungicide with a different mode of action to help prevent resistance to propiconazole developing in your field (Please see the 2014 Maine Wild Blueberry Pesticide Chart, Fungicides (PDF)). Other fungicides should be applied as protectants and before infection periods occur.