8th Blight Update and Seasonal Outlook for Nova Scotia- May 18, 2022 (Frost Advisories!)

Wednesday, May 18, 2022

 This update includes frost advisory and blueberry frost risks, monilinia infection period, and recommendations on field activities.


Frost Advisory and Blueberry Frost Risks


Frost Advisories are issued in Annapolis, Colchester (Cobequid Bay, Truro and South, North), Cumberland (Minas Shore, North and Cobequid Pass), Digby, Hants and Kings. https://weather.gc.ca/warnings/index_e.html?prov=ns.


Please check the link above for areas in the province affected by frost this evening.


As we are starting to see open flowers and bee hives ready to go out, concerns raised about spring frost injury.


Frost injury is a combination of low temperatures, freeze duration and plant growth stage.

As blueberry plants advance into the bloom stage, they are less tolerant to cold than when they are in the bud stages. Please check the figure below for general blueberry stages and each stage’s minimum cold tolerance temperature. When blueberry plants have fully open flowers, any temperature below -2.2c for a couple of hours could damage those flowers.


Figure 1. Blueberry Frost Risks



Monilinia Infection Period


We had an infection period for the last two days through most areas in the provinces. Besides late fields and the Cape Breton area, most fields are quickly approaching the end of the blight infection season. Flowers are starting to open and some growers are starting to put bees out this weekend.

In Cape Breton, just by talking to growers in the area, it is at the 40% F2 stage so closely monitoring weather conditions in those areas is important for growers managing fields in Cape Breton. Fields that have just reached the 40% F2 stage would be susceptible to infection.

                       Figure 2. Wild blueberry susceptible stages to monilinia blight infection

We had a small infection period (the first one for the season for most areas) starting May 4 evening to May 5 morning, but at this time, I haven’t seen any symptoms of infection. I will report if I start to see symptoms.


Recommendations on Field Activities



For the last two weeks, we observed fast plant development and flowers are starting to open. In some fields and areas, it is ready for pollination. I already heard from a couple of growers who already placed their hives in fields and some are considering putting them out this weekend. Please start your communication with your beekeepers and make sure you talk to them if you decide to spray any products when bees are in the fields.



Botrytis blight:

If you are in areas where typically more prone to botrytis infection, such as coastal areas, wet/fog areas and if your fields are weedy (sheep sorrel is an important host) with very dense patches, you should consider and monitor the situation for treatment application. The fungus begins to sporulate at early bloom, so the best time to apply (if needed!) the first application is when about 30-40% of the flowers are open. Closed flowers are resistant to infection. A second spray can be applied about 7-10 days later.