The yellow test papers that indicate spray coverage on your crop is one method of evaluation, Ion Staunton* writes.

There is another. It is called a bioassay and it takes you less than 30 minutes to set up and find out what the optimum travel speed, pressure, droplet size and nozzle angles to deliver the best coverage/kill possible.

It is real. You will definitely know how many pests are killed… or missed; you’ll find out how effectively your equipment is delivering droplets to the target pests. That’s the ultimate assessment.

We know that pressure affects droplet size. So does the choice of nozzle type. The combination of the two plus speed of travel delivers your L/ha (or L/tree).

Large droplets follow the same general trajectory away from the nozzle until they hit (or miss) the plant. The really small droplets can float off without settling on the plant or the insects eating it. Somewhere between these two extremes is what you will settle on as your application technique into the future.

If you find out you can get close to 100% kill with less litres than your current set-up… that will be money saved. Or you might find out you’re missing too many pests with your current technique/rate which could be why you are applying more often… or losing money from less presentable produce.

You might even decide that you have the wrong equipment for your crop. That will cost you, but you’ll get it back over time.

Here’s what you need to do a simple bioassay and find your ideal set-up:

- Living pests in your crop

- Adjustable equipment

- 30 minutes or so to make test sprays and compare results

- An instant-kill insecticide, so the 30 minutes doesn’t become half a day.

Py-Bo Natural Pyrethrum Insecticidal Concentrate kills every insect it contacts… almost instantly. It is registered for use on all fruit and vegetable crops, cut flowers and ornamentals for the widest range of pests so legally, you can use it on almost anything.

Pests die in a couple of minutes (large caterpillars will take, say 20 minutes, but at least you’ll know they’ve been contacted because they will be twitching/convulsing within the first couple of minutes and will bail out from the tree, suspended on a thin silk strand).

Natural pyrethrum is rapidly degraded by mammals so what gets on your hands as you touch your crop looking for dead/living pests will be metabolised by bedtime. You can’t build up to chronic symptoms. And you can pick tomorrow if necessary because there is only a 1-day withholding period.

Procedure for the Dead-Pest-Test:

1. Dilute 1ml/litre of Py-Bo in your tank (1L/1000L)

2. Find a patch of crop with living pests

3. Using your current set up, spray to both sides of say the last 2–3 trees in a row

4. Stop. Spend a few minutes checking. Dead/dying insects have definitely been hit

 - Insects unaffected after a couple of minutes… haven’t been hit by the chemical

5. Adjust something physical: pressure/droplet size/angle or type of nozzles/speed

6. Spray another couple of trees, next row over

7. Check the results; if needed adjust again.

However, if you got 100% the first time, reduce the application a little. You can’t kill them deader than dead so, re calibrate and re-test as above and if you’re still getting close to 100%, you’ve saved chemical, time and money… forever!

If you’re a commercial grower and want to see if I really am biased or not, scan this QR code, scroll down to the yellow panel, and I’ll post you a free 1 litre to try… that’s 1000L of spray to play with.

*Ion Staunton is an entomologist and manufactures Py-Bo Natural Pyrethrum Insecticidal Concentrate. Pestech.com.au 0407 30 88 67.