Monilinia Blight Forecast Post #8 May 17th

Friday, May 17, 2024

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!