Monilinia Blight Forecast Post #9 May 17th

Friday, May 17, 2024

The weather forecast has changed drastically for Saturday going into Sunday with warm temperatures and rain.   For sites with active apothecia this will represent a significant risk of infection and growers should keep an eye on this system.  

If growers have not sprayed in the last week, with a product covering Monilinia they should do so either before the rain event or use a product containing a group 3 directly afterwards.  

Growers may want to chose a product with a broader range of activity at this time to cover Botrytis and Anthracnose as well as Monilinia Bligh such as Miravis Neo or Propulse.  

On a positive note a little soil moisture is very welcome, as we head into bloom, as adequate soil moisture can aid in pollination.  If this rain event does not occur growers should make sure they are on top of their irrigation though bloom in order to help with pollination.   

Monilinia Blight Forecast Post #8 May 17th

Across all sites from Waterville to Aylesford, apothecia that I have found have dried up and are no longer releasing spores.   Therefore, there is little risk of infection going forward (or for the past week as it has been dry).

Looking back over the past month and a half it has been a relatively poor (but good for growers) season for Monilinia blight infection.  There were really only 2-3 serious infection periods for the valley area.  Northern Nova Scotia may have experienced more frequent periods with their more frequent rain events.

The other factor, besides moisture, growers should keep in mind is temperature.  When rain events occurred this year, the temperature tended to be quite cool.  Monilinia at a minimum requires 10 hours of leaf wetness at 8c for infection to occur.  If the temperature is warmer than 8c the infection takes much less time.

All this to say, I don’t believe we will see a lot of infection this year because we didn’t receive a lot of precipitation when the apothecia were active, temperatures were cool during the rain events and growers had time to apply fungicides between rain events.   

Growers should take time over the next few weeks to scout for infections, noting were hot spots for Monilinia blight occur and which varieties are susceptible.  This will show growers where to concentrate scouting and treatments in the future. 

The first signs of infection will show up as blighted tissue (image a and b).  Fungal conidia will then be moved from the infected tissue to flowers by bees (image c) causing mummy berries to develop.  

Image taken from: McArt, Scott & Miles, Timothy & Rodriguez-Saona, Cesar & Schilder, Annemiek & Adler, Lynn & Grieshop, Matthew. (2016). Floral Scent Mimicry and Vector-Pathogen Associations in a Pseudoflower-Inducing Plant Pathogen System. PLOS ONE. 11. e0165761. 10.1371/journal.pone.0165761.

The picture below is a great diagnostic aid to help growers distinguish between Monilinia infection and Botrytis twig blight.

Taken from University of Maine Extension.  

As the weather remains dry going into bloom growers are reminded that proper irrigation is essential through the bloom period to help with pollination, keeping the pollen sticky and flowers attractive to bees!