By Kathryn Carter, Dr. Wendy McFadden-Smith and Amanda Green, OMAFRA
The hot weather has continued to push degree day accumulations (GDD) forward and as of June 15, 2020 the GDD from this year are now ahead of last year’s growing degree day accumulations. The GDD accumulations for 2020 (base 5 °C) for the Niagara Parkway South area are 561 GDD, as compared to the 6 year average (2014-2019) of 588.5 GDD.
Day time high temperatures over the past week have ranged between 17.3 to 22.7 °C. We are expecting the rain storms early in the week next week (Monday and Tuesday) which will be welcome, as soil moisture levels are starting to dry out.
Tender Fruit and Fresh Grape
In Niagara and southwestern Ontario peaches and nectarines are 25 cm and pits are still soft. Plums are 29 mm and pears are 20 mm. Tart cherries 18 mm and are starting to colour up. Fresh grapes are starting to bloom.
Pruning stone fruit trees continues. Fruit thinning has started in orchards.
Bacterial spot symptoms have started to become apparent on foliage in peach, nectarine, plum and apricot blocks following the warm rainy weather we’ve experienced in Ontario recently. Bacterial spot multiplication in leaves is favored by wet conditions that cause water congestion in plant tissue. Rains, dew and high relative humidity assist bacterial entry into plants and multiplication. Fruit are very susceptible to infection as soon as they are exposed at shuck split through pit hardening but new infections can develop until harvest. Severe fruit infections are more common when frequent periods of rainfall or even extended heavy dews and very high humidity occur from late bloom to near pit-hardening. Cueva (copper octonoate) is the only product labeled for bacterial spot in stone fruit. Sprays should be applied prior to rainfall but with enough time for the product to dry. Slow drying conditions will increase the probability of injury to leaves by copper sprays as will repeated applications.
Peaches are most susceptible to peach scab during the shuck-split stage of growth. Because they lack fuzz, nectarine fruit can be infected earlier than peaches: 1–2 weeks after petal fall. Although fruit may become infected shortly after shuck split and continue to be susceptible to infection throughout the growing season, symptoms are typically not visible on fruit for six to ten weeks so only those infections which are initiated between shuck split and six weeks before maturity will exhibit symptoms before harvest. Fungicides with activity on peach scab should be used in blocks with a history of peach scab until 6 week pre-harvest.
Nectarine fruit are now susceptible to powdery mildew infection. High humidity and overcast skies are optimal conditions for powdery mildew proliferation.
Cherry leaf spot and powdery mildew should be managed in tart cherry orchards, even if crop has been lost to hail or frost. These diseases can defoliate trees and reduce tree cold hardiness and productivity in subsequent years if left uncontrolled.
Fire blight infections in pear were promoted by bloom infections followed by severe weather. Infected shoots should be removed (broken off if possible) once terminal growth is completed. Hatch of eggs for second generation has started. Growers should be monitoring the population to determine spray timing and choosing products with activity on motile stages.
Vitis vinifera cultivars have not started bloom yet or are just starting to bloom. Hybrids like Foch and Seyval are at 50-80% cap fall. There are many factors that impact fruit set in wine grapes including weather, vine nutrition and health, vine vigour/balance and cultivar. To learn more about factors affecting fruit set in grape download this weeks podcast on the blog: https://onfruit.ca/podcast. The podcast is also available on most podcast platforms including Apple Podcast, Spotify, Google Podcast, TuneIn and Stitcher.
Vineyard planting is continuing and shoot thinning and suckering is ongoing.
Sporulating downy mildew has been found on foliage and flower clusters in some vineyards. Infections this early in the growing season usually mean it will be a challenging one to manage fruit infection as well. Black rot lesions have also been found in low severity. Powdery mildew is also likely present in trace amounts but hasn’t been detected yet. Growers should focus their most effective fungicides for the early bloom through bunch close to protect fruit during their susceptibility period. A reminder that Rovral is no longer an option for bunch rot control in grapevines as of June 20, 2020. Potato, grape, three banded and Virginia creeper leafhoppers are becoming more prevalent in vineyards with the warmer dry weather.
Nutrient levels in grapes can be assessed either at bloom or at veraison. Petiole sampling provides the opportunity to address any nutrient deficiencies this growing season. Although soil samples provide useful information petiole samples really provide important information on what nutrients the vine is accessing and are helpful in determining nutrient deficiencies.
At bloom collect a total of 100 petioles from leaves located opposite the first or second flower cluster from the bottom of the shoot. Collect no more than 1 or 2 petioles per vine. Dry petioles at room temperature in a brown paper bag for 24 hours and submit sample to lab for analysis. For additional information on petiole sampling refer to Soil Management, Fertilizer use, Crop nutrition and Cover crops for Fruit.