Mummy Berry Forecast 2017 - #2

Wednesday, April 26, 2017

A quick reminder that primary infection of mummy berry disease in highbush blueberry requires three conditions to be met:

  1. Inoculum presence – mature sporulating apothecia cups;
  2. Susceptible bud development stage – vegetative buds have 5 mm of green tissue exposed and flower bud scales are separating (F2 stage);
  3. Suitable weather conditions – long wet periods at relatively warm temperatures.
On Tuesday April 25 we found a few dried up initials but no apothecia cups, and as such no inoculum at this time.  However, if we get rain, initials will likely continue to grow, or new ones will emerge.

Flower buds at F2 (bud scales separating)
There is a report from South West Nova Scotia that some varieties are at the 40% F2 stage. I have no reported fields in Central Nova Scotia that are at the 40% F2 stage. However, with the forecast of warm weather for the next several days, growers should begin monitoring their fields to determine the level of bud development.  Bud development differs greatly from one area to another, so growers must take the time to inspect their own fields and have the fields sprayed at the proper time.

Correct timing of the first spray is critically important for good control. Treatments should not be considered until greater than 40% of the fruit buds are past the F2 stage and there is no need to spray if you have no history of mummy berry disease on your farm. For more information and pictures refer to “Management of Mummy Berry in Highbush Blueberry”.

Table 1. Wetting duration (in hours) associated with mummy berry infection at different air temperatures in Nova Scotia, Canada (Data from Paul Hildebrand and Rick Delbridge).

Note that several fungicides registered for mummy berry disease (eg. Topas) have what is referred to as “back-action” activity and can effectively control an infection if applied within 72 hours of the beginning of the infection period. For a complete list of registered products please refer to “Highbush Blueberry Insect and DiseaseManagement Schedule”.

Finally, please remember that the observations and recommendations above are derived from data collected in Kings County, Nova Scotia and may not be applicable to your location. If you are to the south and/or west of Kings County you may well be ahead in development and if you are located to the east of the Valley you will generally be later. This forecast is to be used a guide only for mummy berry disease management in Nova Scotia. 

Look for the next update late in the afternoon on Friday, April 28th.