Spray workshops

In March, TNZ hosted 2 practical spray workshops to address some issues that might be hindering growers when they spray their crops. Dr David Manktelow is a spray application specialist and had many tips and tricks to share. We are currently editing a video which we hope to be able to share with you soon after this magazine is published, but in the meantime here are some things you can already think about: 

Know where the pest you’re targeting sits in your crop and the coverage requirements of the agrichemicals you use. For example, whitefly adults are likely to be in the top section of the plants, on the underside of leaves.  Efficacy for most soft whitefly control chemicals requires direct contact with the pest. 

The 110o flat fan nozzles that are fitted to many tomato vertical spray booms, project about half their output downwards, which means spray coverage to leaf undersides is compromised.  In the workshops, David demonstrated how a pair of 40o hollow cone nozzles more efficiently projected spray upwards into the canopy and significantly improved under-leaf coverage.     

The workshops emphasised the need to visualise spray coverage and then compare coverage achieved from changes to spraying practices by using folded water sensitive papers.  Two ways to use the papers are 1) pinning them through your crop target area, and 2) clipping horizontal and vertical papers up a vertical spray pole. These are shown in the coming video. 

Before spraying always check your filters and nozzles, clean them if required.  

Always check the product labels for application rates and other use instructions.  Once you have an appropriate spray tank mix, the size of the spraying target should dictate how much spray volume you need to apply.  

You will need to make adjustments according to the age of the plant – a plant with more or less foliage and the density of plants will require different volumes of spray. 

There is no point in spraying past the point of run off as this will mean you are essentially spraying the floor and wasting your money! 

If your spray equipment allows it, spraying opposite row sides from the opposite travel direction will almost always provide better spray coverage than spraying both sides from the same travel direction.    

Because greenhouse growing means there’s no rain to disperse the spray mix, it needs to land in the right place. Using an appropriate adjuvant can help improve spray coverage.  That is a large subject that deserves its own article and video! 

Make notes and take photos! Each time you make a change to your sprayer set up, use water sensitive papers to determine if the change was positive or not. Your photos and notes will allow you to repeat what worked well. 

Finally for now, if you have the ability to add air assistance to your sprayer, this can significantly help to improve spray coverage and it opens up an opportunity to use lower volume concentrate sprays.  Again this is a large subject that deserves its own coverage. 

There’s a guide to sprayer set ups available here and when ready the video will be posted here too: www.tomatoesnz.co.nz  

Thank you to NZ Gourmet for allowing us to host this workshop in one of their capsicum GHs. 

Spray papers before adjustment

 

Spray papers after adjustment

 Greenhouse maintenance