Mummy Berry Forecast - April 29, 2016

Once again, primary infection for mummy berry disease in highbush blueberry requires three conditions to be met:

1. Inoculum presence - mature sporulating apothecia cups,
2. Susceptible bud development stage – bud scales separating in flower buds (F2 stage), and
3. Suitable weather conditions – long wet periods at relatively warm temperatures.

Also, it is not recommended to spray until 40-50% of buds of a given variety are at the F2 stage and there is no need to spray if you have no history of mummy berry disease on your farm.

Observations as of Thursday April 28^st:

• Mature apothecia cups are now present and actively sporulating so we have inoculum present at this time.

• The early variety ‘Bluetta’ had 70% of flower buds at the F2 development stage while the mid-season variety ‘Bluecrop’ was found to have 50% of its flower buds at the F2 stage. The late mid-season variety ‘Nelson’ was at 10% F2 while the late varieties ‘Jersey’ and ‘Burlington’ were at 0% F2. Surprisingly, the early variety ‘Duke’ was only found to be at 10% F2 but it appears most early and mid-season varieties are now at the ideal development stage for infection.

• A 15.5 hr long wet period from Saturday afternoon April 23^rd through to early Sunday morning April 24^th would have been sufficient for a high risk infection period but most (if not all) varieties would not have been at a susceptible bud stage and very little (if any) active spores were present at that time in Kings County; however, we can now say that we are now in the primary ‘mummy berry infection season’ and must either use a “fixed sprayed schedule” to protect bushes from infection or a ‘weather based spray program’ to control infections using controls that have “back-action” capability (eg. Topas).

Recommendations:

A ‘fixed spray schedule’ may be used to manage the disease whereby the first fungicide spray should be applied when 40-50% of the flower buds have reached the F2 stage (flower bud scales separating). One or more additional sprays may be required on a 7-10 day schedule. As such, most early and mid-season varieties would benefit from their first cover as soon as possiblewhile sprays to later season varieties may be delayed until their bud-development reaches the recommended 40-50% F2 stage.

 

Alternatively, a ‘weather based spray schedule’ may be employed. This strategy uses temperature and leaf wetness duration to determine if an infection period has occurred. If an infection period occurs and mature apothecia are present, and flower buds have reached the 40-50% F2, then the grower has up to 72 hours after the start of the wet period to apply Funginex, Mission, or Topas. An additional spray(s) may be required, depending on weather conditions, 7-10 days later. Identification of infection periods for back-action control will be communicated through this forecast in the coming weeks so please stay tuned and have your sprayers ready.

 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. Once again, if you are to the south and/or west of Tim’s location in 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.