How common is powdery mildew at that stage at this part of the season? Would a sulphur spray be effective or should I be using something more powerful?
Hi Jenni,It depends on the level of disease. If it is light leaf spotting like that shown in our pictures a few applications of sulphur between now and 30 days before harvest would be appropriate.There are more serious infections that require a different approach.Matt Wilson CropWatch agronomist says; “We have seen the most disease in the usual culprits; machine pruned monsters and breathless areas (sheltered vineyards with low airflow). These vines with heavy canopies increase the chances and longevity of leaf wetness and increase relative humidity.”Matt also says; “The best approach to disease management is to apply preventative fungicide sprays and use canopy management to keep uV light onto your fruit. Powdery (and downy mildew) are diseases that are difficult to control oncethey get a foothold. While we have many effective fungicides for preventative control of powdery mildew in grapes, not many fungicides can eradicate existing colonies. In fact, spraying systemic fungicides on raging infections is not very effective and can encourage fungicide resistance development.
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