Soybean desiccation by drone and spider mite control

Spider mite in soybean: spraying in July

Spider mite outbreaks in soybean follow the weather: they appear as soon as it turns hot and dry, at 25 to 30 °C. Scouting therefore has to start as soon as summer warms up. Mites live on the underside of the leaf, which makes conventional spraying harder, but the drone gets around this: the strong downdraught from the rotors drives the droplets down to the lower leaves and their undersides.

The main problem is the two-spotted spider mite (Tetranychus urticae), which sucks sap from the plant. The first sign is fine greyish speckling on the upper side of the leaf; as the attack builds, the leaf turns yellow, then red, and finally drops, and fine webbing is clearly visible on the underside. Attacks almost always start at the field edges or on higher ground, so those spots are checked first. If the problem is caught early, only the hotspots need treating (PSSS, Poljosfera, 2023).

Like any summer spraying, the treatment is done late in the afternoon or in the evening, once the heat of the day has passed. Advisory services note that the treatment often has to be repeated after 10 days. The choice of product and rate is left to your agronomist, and our pilot Nikola mixes the product at the field. Before every insecticide treatment we notify local beekeepers so they can close their hives.

More on recognising the symptoms and timing control: spider mite in soybean: how to recognise and control it.

Soybean desiccation by drone: when and why

Soybean desiccation means drying the crop chemically just before harvest. It is done once soybean reaches harvest maturity: the leaves on most plants turn yellow and start to drop, and seed moisture falls to about 30 to 40%. Depending on the product and the weather, harvest can start 4 to 14 days after spraying (agromedia, citing advisory services).

Desiccation is often necessary because of how soybean grows: the plant builds a lot of leaf that can stay green even when the pods are fully ripe. This is especially marked in wet years, when soybean ripens unevenly. If that green material goes into the combine, the sieves clog, green and wet debris mixes with the seed, and the buyer deducts for high moisture.

Timing is critical. Desiccating too early cuts seed filling short, reducing yield and thousand-seed weight. Desiccating on time (when moisture reaches 40%) shortens the wait and clears the soybean off the field in time for the best sowing date for winter cereals (PSS Zrenjanin, Poljosfera).

This is where the drone has a clear advantage. A tractor in ripe soybean permanently flattens 5 to 6% of the plants, while the drone does the job without trampling a single stem, using only 15 to 20 litres of water per hectare. After rain, a tractor has to wait for days, while the drone needs only a dry access road to the field. To protect neighbouring crops, we fly only in winds of up to 3 to 5 m/s.

Everything about the process: desiccation by drone. For a longer article on timing and methods, see soybean desiccation: when and how.

Herbicides in soybean

We apply herbicides by drone very rarely, and only as a correction. The tractor is clearly the right tool here: in the early stages after sowing the sprayer runs close to the ground, so the coarse droplet covers the weeds well. We apply herbicides by drone only when heavy rain keeps the tractor off the field for too long and the crop gets ahead, and on the strict condition that the neighbouring fields carry the same crop, so drift cannot harm them.

The weed control programme has three stages: a treatment after sowing and before emergence; a treatment after the soybean and weeds have emerged; and a dedicated treatment against grass weeds, mainly rhizome Johnson grass (ADAMA Serbia). We always leave the choice of herbicide to your agronomist.

Soybean treatment calendar

These windows are standard practice; the exact day always depends on conditions in the field, the forecast and the agronomist.

How much soybean desiccation by drone costs

Soybean desiccation costs €25 per hectare up to 20 ha, €22 from 20 to 100 ha and €20 over 100 ha. Exactly the same price applies to insecticide, fungicide and foliar feeding treatments. You supply the product and the water. Travel within 50 km of Opovo is free; for more distant locations we charge €1 for every extra kilometre.

By comparison, tractor spraying costs about RSD 2,000 per cadastral jutro (around €30/ha), and the tractor also permanently flattens 5 to 6% of the crop.

Worked example: 25 ha near Debeljača (16 km from Opovo), a new client's first order.

A package saves money: three treatments on the same field in a season (for example spider mite, foliar feeding and desiccation) get 5% off, and five or more treatments get 10%. For those 25 ha, three treatments with the discount cost €1,546.60 (an average of €515.53 per treatment). You pay in stages, after each visit. Clients with a package get priority when booking.

Note: we take fields under 10 ha only within 20 km of Opovo.