Post-harvest leaf canopy management worth the investment
By Brandy Rawnsley
Harvest is almost complete with the primary focus on producing the best grapes for purpose. During post-harvest, it’s time to focus on the leaves and setting up for vines for next season.
Leaves are critical for photosynthesis to occur and storage of carbohydrates after harvest. Dormant vines survive on their stored reserves from leaf fall. Carbohydrates, stored as starch and sugar, support new root and shoot growth in the following season.
Lower carbohydrate and nutrient reserves can contribute to poor bud burst, reduced bud fruitfulness and fewer flower numbers.
Premature leaf defoliation reduces the ability of the vine to store carbohydrates. Defoliation can occur by pests and disease, machine harvest impact and heat stress. Maintaining leaves for as long as possible after harvest ensures continued vine health.
Effective pest and disease management during the season is vital for maintaining good leaf canopy until leaf fall. With a well-managed vineyard, there should be no need to apply a fungicide after harvest.
Yet in hot growing regions, vines can retain their leaves up to 3 months until leaf fall. Powdery mildew can still pose a risk during this time. In humid conditions, powdery infections can take hold quickly leading to unexpected early defoliation.
Post-harvest sprays may only assist on vines with a long period until leaf fall, or on young non-bearing vines to prevent early defoliation. A single post-harvest application of a sulphur product such as THIOVIT JET® should protect the canopy from further infection. It’s good to consult your agronomist and consider disease risk before deciding to spray.
In vineyards with known powdery mildew infections, there is a high risk of overwintering structures developing called chasmothecia (formerly known as cleistothecia). These resting spores allow disease to be carried into the next season, especially in bark and on mummified bunches. Remove all mummified bunches from vines to stop carry over of the disease.
If disease has been a problem this season, now is a good time to review your fungicide spray program. Consider factors like product selection, spray interval, application and coverage to set up early disease control.
Together with strategic irrigation and nutrition, maintaining a good canopy prior to leaf fall lays the foundation for success next season.
Dr Belinda (Brandy) Rawnsley is a Syngenta Technical Services Lead for Viticulture and Horticulture.