In-row weeders increasingly handy, manual labor almost redundant

In-row weeders, machines that drive between plants and remove weeds, are gaining popularity. Weeding between rows, especially with the advent and success of camera-controlled hoes, is technically no problem. But now there are also several machines that hoe in the row, between the plants. At a demonstration by Ceres Horti Advice and Delta Plan for Agricultural Water Management in the Netherlands, five manufacturers showed what they could do by completely hoeing a field of iceberg lettuce in one pass. Two of the machines shown, the Steketee IC Weeder and the Garford Robocrop Inrow, have been on the market for several years.

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Hoeing sugar beets with an in-row weeder is possible

Ferrari has also had the technology for a while. K.U.L.T.-Kress is well-known in hoeing technology. This manufacturer is relatively new to this market with its K.U.L.T.iSelect in-row weeder. Completely new to the Dutch market is the Oliver Agro Optyma.

One thing the machines have in common: they work. Currently, the application is mainly in horticulture. Iceberg lettuce is well suited for an in-row weeder, as are various types of cabbage and celeriac. Hoeing sugar beets is also possible in principle, although it is a bit more difficult in practice.

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Software is crucial for in-row weeders​

The principle of the in-row weeder is the same for all providers: a camera recognizes the crop and ‘knows’ where it is. The computer then controls a hoe blade that moves between the plants. Different manufacturers claim to have their own camera. But what they mainly mean is that they develop the software themselves that is needed to recognize plants; or, in most cases, they have a camera developed under their own direction by an external specialist.

Camera technology is not a problem. Translating the photo into correct control of the hoe blades, that is the real art. And also the secret of the blacksmith. For a crop like iceberg lettuce, this is relatively simple. The plants are large, clearly recognizable, and planted in regular intervals. In theory, this would apply to sugar beets as well. But they are more difficult for camera recognition. Lettuce or celeriac are planted, so you start with a clearly recognizable plant that is fairly sturdy in the ground a few days after planting.

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Weeds germinatuie before the beets

In sugar beet fields, weeds often germinate before the beets. There can already be quite a lot when the beets reach the four-leaf stage, the stage that is necessary before you can start hoeing. If the weeds already stick out above the beets, then it’s difficult for the cameras to distinguish the plants. Moreover, for example, fat-hen at certain stages looks a bit like a beet, as they know at Steketee. This company has now managed, by using artificial intelligence, to hoe beets with the IC Weeder. This is currently happening on a limited scale in Germany in organic farming.

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Two blades per row

Recognizing the crop plant is step one. The next step is controlling the hoe. Apart from Steketee, which moves the hoe blades with air pressure, manufacturers opt for hydraulically operated blades. Kress, Ferrari, Oliver, and Poulsen (Robovator) work with two blades moving towards each other. Steketee uses sickle-shaped blades to hoe around the plant as well as possible. Garford is the only one that works with rotating blades. By controlling the speed of rotation, these blades turn around the crop plant. This can be either hydraulic or electric drive. Electric allows the speed to be varied a bit faster, which benefits the maximum achievable driving speed.

Driving speed of in-row weeder: 3 kilometers per hour

As for the driving speed: for all systems, 3 kilometers per hour is a normal driving speed to make the hoe work well. Driving faster is possible, but at the expense of accuracy. Moreover, at too high a driving speed, the blades throw soil up, causing clods to land on the crop plant. Not a big deal with celeriac, cabbage, or a sugar beet, but with iceberg lettuce, a clod can grow into the head.

The Steketee IC Weeder has air on board, and the manufacturer can equip the machine with ‘Airclean.’ Then each plant gets a blast of air to blow clods off the plant. This requires a lot of air for large working widths, and thus a large compressor with a corresponding energy need.

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Further development

The current in-row weeders, with camera technology that continues to recognize crops well and can quickly control a hoe, have an important basic component for other plant-oriented applications, such as spot spraying. Although there does not seem to be a demand for this yet, it’s only a matter of time before the market asks for it. Manufacturers can still perfect their hoes to their heart’s content, but the combination with an autonomous vehicle is also obvious. The capacity of the in-row weeder is not the biggest point for most users. The most important thing is the accuracy with which the hoe works, and especially the amount of manual labor that the machine saves. The camera systems, like those at Steketee, can also be read and adjusted remotely. You don’t need to be on the tractor for that.

Labor savings with in-row weeders

Kress had equipped his machine at the demo in Heerhugowaard with extra cameras, so that the driver can assess the result of the work. That too can be done remotely in principle. In combination with an autonomous vehicle, one person can then keep several in-row weeders at work. This makes the labor savings even greater and the work possibly safer. Because working with a well-functioning in-row weeder at 3 kilometers per hour is boring for a driver, and the temptation is then great to occasionally step off along the way. This happens a lot, and several very serious accidents have occurred as a result.

What does such a machine cost? It depends on the number of hoeing elements, but count on around € 100,000 for a five or six-row machine. Electrically driven and equipped with all options, this can rise to well over € 170,000 at Garford.