Guide · Dairy Australia field video

Fall armyworm: getting the best aerial (drone) application

Drones are a great tool for treating fall armyworm — but they're not the only tool, and not every operator is doing the right thing. Here's what to look for, and what to ask for, so you get the best application at the best value.

Produced by All Flight for Dairy Australia.

"I'm a third-generation pilot from the manned industry and I've been a chief pilot for the last 10 years of rotary helicopters. The drone industry has expanded at a rate the manned industry could only dream of — good, because the technology and cost-effectiveness keep improving; bad, because there are people who now have access to some serious machines and don't really understand them."— Michael Barnes, All Flight

Start with the operator's attitude

The first thing to look for in a drone applicator isn't the drone — it's the operator. Are they rushing, or do they care about your problem? Are they open to discussing the application? Are they appropriately qualified, licensed and insured? And are they thinking beyond the paddock — neighbouring properties, buffer zones, susceptible crops, bees, waterways?

A last-minute loose job gets you loose results. "I can do it cheaper" from the new guy on the block is a red flag — corners are likely being cut.

The paperwork is the point

Before the job, you should have filled in a request-for-application form that sets out your requirements and agrees the application against an aerially-approved chemical label. That's your record-keeping — and it's a legal requirement for both you and the operator. If you're not signing something like this, there's probably not good record-keeping going on. If an application goes sideways without paperwork, you'll be the one left holding the ball.

Proof, not marketing

There's a gap between what manufacturers market and what's real. We pattern-test our applications before every new job, using the Dropflight app. We lay out water-sensitive paper set one metre apart across 20 targets and fly the centre line, which lets us account for drift and calculate fines. That gives us a baseline of our swath, our droplet size and the actual coverage at target — the app calculates effective swath and uses an overlap model so we can tune swath width for the best coverage.

Every application's water rate, droplet size and speed is different depending on the target, crop size, condition and foliage density. Ask your applicator about their swath testing — you might be surprised to find they haven't done it.

Timing: kill them before they enter the cob

With fall armyworm in maize, the most critical spray is at the silk stage — when the silks are fresh and hanging out the end of the cob, and the moths are laying eggs on them. Once the grubs are into the cob you can't get chemical to them, so you have to kill them on the silks before they go in. The best time to spray always depends on the stage of the crop and the pest — it's a conversation between the farmer, the agronomist and the applicator.

Coverage beats water rate

You want high coverage at the target — and that's not the same as a high water rate. Droplet size is what matters: every time you halve the droplet size, you increase the number of droplets by up to eight. Flying slower also helps — it gives better circulation through the crop and better overall coverage.

Finer droplets come with considerations — always follow the label, use the recommended surfactants, and comply with maximum winds, buffer zones and minimum droplet sizes. Spray systems should be tested regularly for droplet-size accuracy, percentage of fines and true effective swath.

Weather: wind and Delta T

Winds have to be on-label, and Delta T within limits — an important factor for aerial application that isn't used much in the ground-rig world. Delta T is the difference between the wet and dry bulb temperatures: a high Delta T evaporates smaller droplets and gives a poor application, while a very low Delta T can leave droplets suspended and cause drift. We use a Kestrel handheld weather station to check the actual numbers at the point of application — the readings Bluetooth to your phone, which is excellent for record-keeping.

From the field

Testing on maize, Tyler and I started at 50 L/ha at 3 m height — but the target is actually a metre into the crop, not at ground level, so we brought the height down to 2 m and got far better penetration (dropping from 3 m to 2 m costs nothing extra). Comparing an 80 L pass to a 50 L pass, the heavier rate was a bit better but nowhere near eight times better — and either way, more litres just means it takes the operator longer to get the product out, which costs the farmer more. The lesson we took: keep the pest under control from the start; once they get bad you can't pull them up.

For about $250 of gear — fluorescent dye (around $15 a test) and a UV torch ($100–150) — you can actually see your coverage in the field at night. It removes the guesswork and shows exactly where the chemical is landing.

The bottom line

Drone application is a powerful, cost-effective tool — but only when it's used correctly and responsibly. Experience, attitude, proper licensing, compliance and verified pattern-testing matter far more than price or marketing. Effective spraying is about droplet size, coverage, weather conditions and label compliance — not simply higher water rates. Smaller, correctly-managed droplets can dramatically improve coverage and results while reducing cost, but they have to be used within the label's environmental limits. Choose an operator who tests, records, complies and takes accountability — because in aerial application, shortcuts lead to poor results and serious risk.

Advisory only — always use registered products to the label, follow APVMA requirements, and treat based on monitoring and your agronomist's prescription. Reference: Dairy Australia — Fall Armyworm.