2023 Updates and Seasonal Outlook for NS_ July 7_ GDD, Crop Development and Weather Updates; Leaf Diseases Management Reminder (Sprout Fields)

Friday, July 7, 2023

GDD, Crop Development and Weather Updates

2023 Degree Day Accumulations (Based on Kentville Data)


We are still below the 5- and 10-year averages for plant and insect development (Figure 1). Currently, it looks like we are only 2-3 days later than last year’s development. I will talk about wild blueberry GDD and crop development next.


Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to July 4 for the past 17 seasons. Provided by Jeff Franklin (AAFC).


·                     Approximately 5% less plant development heat units compared to the 5-year average, and 5% less compared to the 10-year average.

·                     Approximately 10% less plant development heat units compared to 2022, and 16% less compared with 2021.

·                     Approximately 8% less insect development heat units compared to the 5-year average, and 8% less compared to the 10-year average.


Wild Blueberry Weather Station GDD and Crop Development Updates


Figure 2. Wild Blueberry GDD_ July 5


Crop fields: Since we are still researching GDDs for different wild blueberry fruit stages, I don’t have fruit stage GDDs to share yet. Based on our five study sites in Cumberland and Colchester, we are starting to see a couple of blues in the early patches. Overall, most of the fields are heading to the late green fruit (blushing) stage with a small percentage of red fruits (Figure 3). Growers should start to monitor blueberry maggots and SWD shortly.


Figure 3. Wild Blueberry Late Green Fruit (Blushing) and Red Fruit Stages


In sprout fields, most of the mainland fields are around 50% tip-dieback stage (meaning the newly emerged stems stop elongating). Cape Breton fields are looking at around 25% tip-dieback. This information is very helpful in two ways: conducting soil/tissue sampling and developing a sprout field leaf disease management program for the coming weeks. As wild blueberry plants reach the tip-dieback stage, the nutrient leaves are most stable, so this is a good stage to conduct tissue sampling. Based on this season’s weather development, most of the mainland fields can start tissue sampling in 2 weeks. We will talk about the leaf disease management program in the next section.


Weather Update_ June Rainfall

I am sure that we all have the same feeling about June’s weather unless you weren’t present in Nova Scotia. It was wet!

The June weather certainly had impacts on yield this year, especially on pollination and botrytis blight. We didn’t have many good pollination days, but it was variable in regions. It rained almost the entire month with 20 days in June with measurable rainfall (Halifax weather data, from CBC). The below figure gives you a visual idea of how wet it was in June.


Figure 4. Halifax June rainfall (from CBC)

From other weather stations installed in research sites and wild blueberry fields, this past June, rain was recorded on a total of 20 days, whereas the average for June is 14 days of rain.

The last comment on rainfall was provided by my colleagues and this observation was based on Kentville weather data. In terms of quantity, the 25-year average for June is 87 mm but this year 239 mm of rain was recorded. Jeff Franklin explains that: "Extended rainy periods in June and July are not typical but do happen. The years 2019 (June), 2015 (June), 2014 (July) and 2011 (June) all had stretches of rainy weather with 30-day totals over 170 mm, or twice the monthly average. For the months of April, May and June combined we received 315 mm of rain in Kentville compared to the 25-year average of 244 mm. We have more than made up for the dry weather experienced in April and May."


Leaf Diseases Management Reminder (Sprout Fields)


I also like to get growers’ attention and ask you to start thinking leaf disease management program for sprout fields.


Leaf disease management in sprout fields is happening during the harvest period thus growers often invest their full energy into harvesting, which is understandable, but taking care of sprout-year fields is also important.


On the weather side, a humid condition is favourable for disease development (like the 2021 season) and this is what we are experiencing now at the beginning of July. The rainfall we got in June and early July humid weather would increase disease infection.


A few thoughts to share and I hope you can manage sprout fields well this summer.


1.      We have seen more leaf disease infections over the years because of our pruning practice (primally mowing, instead of burning which will help to reduce those diseases in fields) and the summer weather we got in the Maritimes (wet and hot summer days are favourable for disease development). If leaf diseases are severe in your fields, pruning by burning can be considered.

2.      We primarily use fungicides in the leaf disease management program in wild blueberry production. Two very important things to consider are the timings and choices of fungicide.

3.      Important wild blueberry leaf diseases and fungicide products. In Nova Scotia, three leaf diseases are the primary concern for wild blueberry sprout year management. They are Septoria leaf Spot, Leaf Rust and Powdery Mildew. Those diseases occur on a large scale and it was not hard to see them over the years in most of the wild blueberry fields in Nova Scotia. The below figure shows you when those diseases will show up in fields and the timings for a fungicide application to target them.


Figure 5. Sprout year leaf disease control (NB Wild Blueberry Factsheet C.3.3.0)


4.      If Septoria is a main concern for your fields, a fungicide application should be conducted early. Please note, some fungicides use in crop year during bloom and botrytis timing also provide a Septoria control feature.

5.      Most of the time, growers should consider starting their first fungicide application around mid-July (use Leaf rust- red line as your guide in Figure 5). To be efficient and effective, the first fungicide should be conducted prior to harvest. Those fungicides give protection and control ranging from 7-14 days. If needed, after a busy harvesting period, another fungicide application should be considered if the weather is favourable. The second application is to target leaf rush, which seems to be a main concern for NS fields, and powdery mildew. A sprout field with severe leaf rush will have early defoliation as early as August. Leaf rush has a very long infection period (Mid- July to November), so in any given year, if the weather is wet and humid in August, a second application for rush control should be considered.

6.      When considering fungicides, growers can use this guide to identify products: https://www.perennia.ca/wp-content/uploads/2018/03/Wild-Blueberry-Management-2023.pdf.  

A sprout field with beautiful rea and healthy-looking plants. The photo was taken in early November. 
The grower did a great job keeping leaves lasting until late fall which is helpful for floral bud development. 

Enjoy the sun! Have a great weekend!