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.
Hugh