Mummy berry forecast – April 25, 2013

Thursday, April 25, 2013

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.

On Monday this week I reported that there was no inoculum so there was no need to spray.

I can now report that as of Wednesday morning this week, numerous apothecia cups, mostly immature pinheads, were observed at Tim Strong’s farm in King’s County.  The majority would not have been mature enough to sporulate but will be maturing quickly under the warm conditions yesterday and today.

I can also report that early flowering varieties like Bluetta (40-50% F2 stage) are highly susceptible to infection as of yesterday evening, but that most other varieties including Duke (5%), Bluecrop (5%), Nelson (0%), Jersey (0%) and Burlington (0%) were not at a susceptible stage for infection at this time.

Finally, there were suitable weather conditions for infection on Tuesday evening through to Wednesday morning but there have not been suitable conditions since then.

What does all this mean?  Well, at worst there would have been a very small amount of inoculum present at the time of the infection period late Tuesday night through to Wednesday morning and only the earliest flowering varieties would have been susceptible to infection at that time in Kings County.  Growers have the opportunity to spray Topas, Mission, or Funginex within 72 hours of the start of an infection period (7 p.m., Tuesday the 23rd) which would mean that they would need to spray before 7 p.m. on Friday May 26th for “back-action” control of any infections.  In my opinion there would have been very little inoculum present during the infection period in question and it would be highly questionable if a back-action spray would be beneficial and would certainly not be warranted for most varieties that are not at susceptible bud development stage. However, these fungicides are also excellent protectants and if growers wish to make a spray on early flowering varieties for both back-action and protectant benefits for the next 7-10 days this may be beneficial.

Lastly, please keep my comments in the context of the conditions in Kings County.  If your blueberries are further developed than Tim’s in King’s County and/or you had a longer wet period you may well benefit from a back-action spray as discussed below.  Conversely, if you are behind in bud development a back-action spray would not be beneficial at all at this time.

The other take home message from this report is that we are essentially entering the mummy berry infection season and we have to be on guard for infection conditions over the next 3-4 weeks.  To review the combination of conditions (leaf wetness and temperature) required for infection you may find it beneficial to review the mummy berry management factsheet on Perennia’s website.

No comments: