6 August 2024:
Hello
Dear Readers!
I have been
out on the road again last week… checking in on growers and seeing the seasonal
progression. I will be in the Malagash area this week and looking forward to
seeing you again. A report of my visits will be posted in my next blog.
In the
meantime- some updates:
OFCAF
Cover Cropping Session:
A big thank
you to everyone who participated and attended the Perennia-OFCAF Cover Cropping session last
week. We had a good turnout, many questions and good insights. A follow-up
session will be organized in due time. Please
remember- cover crops do much more than allow for machinery re-entry after
adverse weather conditions. Contact us for more information and find out how OFCAF
can support you and your vineyard.
As we continue
into August, and as mentioned previously, I will be posting the Blogs more often.
The
Weather:
I am sure
most, if not all of us received the flood warning on Sunday. According to our
Davis weather stations, the North Shore received no rain over the weekend while
Kentville-Wolfville about 7.5mm; Bear River about 1.2mm over the weekend.
Disease
and Spray Schedule:
With the combination
of humidity and the significant precipitation here in the valley and wider out,
many growers have been contending with Black Rot and Downy Mildew. Pease do
make sure that even if you don’t have black rot, you spray for it regardless.
Here is some
Black Rot Information you may find useful:
Acknowledgement
goes to Wendy McFaden Smith and Marton Szabo et al. Please see the citations at
the end of this article if you require further information and links for
further reading.
Black
Rot:
Below is a
diagram of Black Rot Development and explanation of why Black Rot is so
damaging to vineyards.
Figure1. Disease cycle of black rot of grapes.
Source: Black
Rot of Grapes (Guignardia bidwellii)—A Comprehensive Overview. Horticulturae
2023, 9, 130. https://doi.org/10.3390/ horticulturae9020130; Statistical Report
on World Vitiviniculture. https://www.oiv.int/en/statistiques/recherche.
The pathogen is active for several infection cycles in one season. The inoculum produced in one season can be carried over to the next one, leading to the accumulation of inoculum over the years. This is why it is so difficult-almost impossible to eradicate.
Conditions
for Infection:
A constantly
moist leaf surface is needed for the infection process to begin; the lower the
temperature, the longer this process takes. When these conditions are met, the
spores can germinate in 36–48 h and then penetrate young plant cells. About two
weeks later, at the sites of the penetration, brownish lesions are observed on
leaves, shoots and berries on which black spots appear. These spores again reproduce
repeatedly and attack all parts of the plant during the growing season.
Early
Springtime Infection:
Depending on weather conditions, vines are most susceptible 1‐5 weeks after flowering.
The
fungus spores form in the springtime under adverse weather and infect the green
vine tissue. The majority of the spores are dispersed, and the plant infected by
the end of flowering. What was not released during the dry period continues to do
so after further rainfall events. Additionally, any spores from mummies left on
the ground can be released not just in the beginning of the growing season but
from bud break through mid‐summer.
Continuous
Infection:
Spores
continue to be produced into late summer from mummies that are retained in the
canopy, thus providing continuous primary infection. Spores are also air borne
and can therefore travel wide distances. The secondary infection occurs
as rain drops splash and carry the infection.
Infections generally
decline in late July and disappear by late August- at full berry development.
Fully
developed adult leaves and berries after the onset of veraison are not
susceptible to infection.
The
fungus can, however, persist on infected vine debris for up to 2 years.
PREVENTION
Sanitation is Key
- After harvesting, the amount of infective material can be reduced below critical level by cutting and removing mummified clusters.
- The removal and destruction of the first infected, symptomatic leaves found during shoot thinning is a beneficial method for cluster protection.
- If equipment is being shared or moved from a black rot affected vineyard, remove all debris from the equipment to avoid further contamination and black rot dispersal.
- An airy, thinned canopy and keeping rows free of weeds will ensure that leaves dry quickly after rainfall, reducing the risk of infection.
- Low cover cropping can also reduce relative humidity in the canopy.
- Any practice that limits or prevents physical damage to grapes and clusters is important.
- A balanced supply of nutrients reduces the susceptibility of the vine to diseases. It is strongly advisable to avoid excessive nitrogen supply to prevent extreme vegetative growth.
A Combination of Strategies
To To achieve successful black rot control, strategies should combine sanitary measures, cultural techniques and the timely use and good coverage with effective fungicides.
Fungicide options can be found in the Online Perennia Spray Guide. Excellent coverage can be obtained from immediate pre‐bloom stage through 4 weeks post bloom. Spraying should start at least 2 weeks before flowering if the disease was severe the previous year.
Please note
that for organic practices, only prevention options are available. Application must
be repeated more frequently if rainfall events occur.
Aim of Fungicidal
Sprays:
The aim of
the treatments is to prevent the accumulation of infective material by
all possible means, because it is not the mass of infective material
accumulated in a given year, but the mass of infective material
accumulated over several years that pose serious risk of epidemics.
I hope that this was helpful. If you require further information, please contact me.
Before I sign
off, here is a quick GDD update from Jeff Franklin at the Kentville Research
Station. The follow up to this post will include growth stage updates and
cultural practices going into Veraison.
Table 1. Precipitation totals for the Kentville Research and Development Centre by month.
|
Month |
25-Year
Average (mm) |
Current
Year (mm) |
|
April |
81.5 |
54.0 |
|
May |
74.0 |
29.8 |
|
June |
95.5 |
83.0 |
|
July |
81.3 |
201.7 |
|
August |
94.5 |
*0.0 |
|
September |
104.1 |
|
|
October |
115.8 |
|
* Up
to August 1, 2024
Table 2.
Growing degree days
and Sine degree days up to August 1, 2024. All temperature data were recorded
at the Kentville Research and Development Centre.
|
Single
sine degree days, base of 0 °C starting on April 1 |
Growing
degree days, base of 10 °C starting on April 1 |
||
|
Current
Year |
10-Year
Average |
Current
Year |
10-Year
Average |
|
1785.1 |
1681.1 |
715.4 |
609.4 |
Thank you all for your time and see you soon.
Cheers!
Katarina
Sources:
Black Rot of Grapes (Guignardia bidwellii)—A Comprehensive Overview. Szabó, Márton et.al. Horticulturae 2023, 9, 130. https://doi.org/10.3390/horticulturae9020130. https://www.researchgate.net/publication/367260346_Black_Rot_of_Grapes_Guignardia_bidwellii-A_Comprehensive_Overview
Why is black rot so bad in some Ontario vineyards in 2024?
McFadden Smith, Wendy. July 26, 2024
Katarina Vucic
Viticulture Specialist
Perennia Food and Agriculture
Email kvucic@perennia.ca
Office 902-678-7722
Cell 902-599-1390
