Seasonal update 2022: GDD, precipitation, berry development and fungal disease management

Jeff Franklin, from AAFC Kentville, is sharing with us this week weather information after a second heat wave. Last week brought an important amount of heat units, in some cases it was possible to see the vines lightly limp and nothing of precipitation at all. At the beginning of this week the situation has changed, precipitations re-filled the soil profile to continue with the proper berry development.

The first table shows the temperature base 5⁰ C and 10⁰ C from 2019 until 2022 accumulated from March 1 until August 8. At the end of each section, it’s possible to see the average of the last 5 and 10 years respectively.

Category	2019	2020	2021	2022	5 year average	10 year average
Plant development (Base 5ºC)	1148.8	1264.2	1305.7	1329.4	1251.3	1256.4
Insect development (Base 10º)	645.3	777.0	763.4	791.9	739.4	741.0

Figure 1. Degree day accumulations as of August 8, 2022.  All data are taken from the Kentville weather station, based on a start date of March 1, and calculated using the single sine method.

At this time, we can see 2022, after the heat wave, with higher values than 2021. Also, compared to the 5- and 10-year average, it increased the accumulation in 2022 the last 7 days. This increase of temperature has accelerated in some places the berry growth and at the same it’s possible to see in grapes with sun exposure symptoms of sun burn.

In the following column graph, you can see the values from 2004 until 2021 and at the end the average of the last 5 and 10 years respectively.

Figure 2. Degree day accumulations as of August 8, 2022 base 10⁰ C. All data are taken from the Kentville weather station, based on a start date of March 1, and calculated using the single sine method.

As previously mentioned, the trend changed due the heat wave of last week. Currently, 2022 is higher than the 5- and 10-year average. Compared to previous seasons, the differences are smaller, it is slightly higher than 2021 and the most notorious year is 2006.

Figure 3. Precipitation in millimetres (mm) registered in July. All data are taken from the Kentville weather station.

Precipitations was very low throughout July, with only 36 mm registered in Kentville research station. Jeff commented that distribution of rain throughout the province has been different depending on the location. He mentioned ‘as an example, Greenwood is reporting 76mm of precipitation compared to our 36mm for July’. Therefore, the last precipitation received at the beginning of this week are welcomed.

Already mentioned, the heat wave brought an important accumulation of growing degree days to the area, which helps to grape development. In some cases, where the grapes were more exposed to the sun, it’s possible to see some sun burn symptoms on the grapes. This damage can stay on the grapes, it’ll be mainly on one side of the bunches, the side with more exposure to the sun. In the following photo it is possible to see a bunch with sun burn and mechanical damage.

Figure 4. On the left bunch with sun burn and mechanical damage and, on the right, additionally to the previous symptoms the small berries due humidity at pollination.

Berry development is still moving along, hybrids as usual are moving ahead of time compared to Vitis vinifera ones. In some cases, hybrids reached bunch closure, while in others the bunches are lighter due humidity conditions at bloom. On the other hand, vinifera ones are behind, depending on the location this condition can change. Like hybrids, it’s possible to see bunches without all the berries, which might be related with the humid conditions at bloom.

Figure 5. On the left Castel and on the right L’Acadie.

Figure 6. On the left Chardonnay and on the right Pinot noir.

Mentioned the last couple of weeks, Downy Mildew pressure has been quite high with the current conditions, high moisture, and warm temperatures. Even though the conditions have been changed to less humidity and warmer, such as last week, these conditions can be suitable for other diseases such as Powdery Mildew. It’s necessary to keep an eye in the vineyard for symptoms on the canopy or the clusters.

Figure 7. Leaf with desiccated Downy Mildew this week.

It has been recommended the last couple of weeks to:

• Scout minimum 3 times per week the vineyard
• Check the most susceptible varieties, and
• Spray according to the situation.

Moreover, it’s necessary to check other diseases as well, differentiate with other fungal diseases to spray the proper fungicide to keep control in the vineyard. For this information and to have an access to the Grape Production guide, please check the previous publication in the following link about Downy Mildew management tips.