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Should I spray after a frost?

It’s been great weather for surfing monster swell at Streaky Bay but we’ve had a few chilly nights in the last few days and a few more coming by the looks – so should we be spraying or not?

Spraying around frosts can affect efficacy and in some cases give crop damage. Ideally plants need to uptake the chemical sprayed on them and they need to actively growing to do this.

The old rule used to be:

1. After one frost – don’t spray for 24 hours

2. After two frosts in a row – don’t spray for 48 hours

Recent work by Chris Preston, University of South Australia, has shown that the weather AFTER spraying has more effect on efficacy than BEFORE spraying. His results (below) showed that that cold weather before his application had little effect but cold weather after spraying had a larger effect. The amount of clethodim required to reduce biomass by 50% doubled with frost treatment after the first application.

Taking this into account a better rule would be:

1. Don’t spray if frost is forecast for the following day

2. If frost or extreme cold weather occurs after application expect a variable result or a very slow result.

3. There are many different types of frosts – some plants are still frosted at lunchtime whilst others are gone by 9am – but ensure the plants are actively growing to get the best spray result.

Please take this into consideration when spraying over the next few weeks especially if you are grass-freeing.

We might be better off waxing up the surfboard and heading to Streaky for a few days!!

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