Tuesday, 11 December 2018 12:23

Finger on the pulse of powdery mildew

Written by  Anna Lambourne and David Manktelow

Sprayer setup is the most important of the different factors that contribute to effective powdery mildew control.

It doesn’t matter if you have the perfect timing and use the perfect chemical strategy, if you don’t get good coverage it will fail. 

Sprayer setups need to be adjusted as your canopy grows through the season and tweaked to improve performance in different canopies. Significant improvements can be achieved from very simple fault checking and tuning of sprayers. 

 Key messages 

- Prioritise sprayer repairs and maintenance

- Use the ‘New Zealand Winegrowers - Setup guides’ to help you set your sprayer up correctly 

- Check coverage

- Recheck setup throughout the season

Prioritise repairs and maintenance 

Sprayer operators can only achieve good results if the equipment they use is up to standard. Prioritise repairs and maintenance on your sprayers. Far too many sprayers are being operated with needless and fixable faults – for example; bent dropper arms, kinked (obstructed) hoses, leaking air ducts, poorly cleaned filters and nozzles, asymmetric setups and, blocked or missing agitation systems. Leaving these type of problems unresolved will result in problems.

Make sure your sprayer is serviced, but remember a sprayer service will oil and grease, but will not check setup. 

Set up your sprayer

Use the ‘NZW Sprayer setup guides’ as a starting point for angles, numbers, pressures and speeds that have proven effective in most NZ canopies. 

Take time to look at your sprayer, park it in the row and check it over. Is the setup symmetrical – the same on both sides?  If one row side or the heads in adjacent rows are different then chances are that one side will be doing a better job than the other – decide which is best and make them all look like that. 

Chose which nozzles are needed and block off the rest. Check the nozzle distance from the canopy is correct and even? Are the nozzles pointing in the right direction? Then run the machine and watch, are there any blocked nozzles and is the spray hitting the target? Check spray coverage using water sensitive papers, if you’re not happy check your setup or your speed. 

Recheck your sprayer routinely throughout the season, especially before the critical growth stages -pre-flowering and pre-bunch closure. Things get bumped, nozzles get lost and things break. Look after your sprayer it is the last and most important line of defence against powdery mildew. 

Nozzle selection

For powdery mildew and botrytis sprays you want to achieve the best coverage in the bunch zone to protect the fruit. So split the spray output. Aim to have 60% of the output at the bunch zone and 40% to the rest of the canopy. To achieve this, consider what nozzle sizes you are using. 

Remember nozzles wear over time, resulting in inaccurate output rates, so make sure you replace them regularly, the cost to do so is tiny compared with the cost of chemicals and even smaller than the cost of pest of disease control failure. 

 

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