Written by Darryl Matthews
Selective spraying is the technology of detecting weeds in a crop or on fallow ground and only spraying the weed. The reduction in herbicides can be between 60% and 90%, depending on the weed density in the field.
Detecting weeds in a fallow field is a technology that has been around for nearly 20 years and treats large acres in the southern hemisphere’s growing regions of the world. The fallow selective spray system detects a green plant in the fallow ground and only sprays the green plant.
There are two types of selective spray systems: brown on green, which detects green plants in fallow ground only (John Deere See & Spray Select, PTx Trimble WeedSeeker 2, Weed-It,) and green on green, which can detect weeds within a crop (John Deere See & Spray Ultimate, PTx Trimble Bilberry, Greeneye Technology, and One Smart Spray). Depending on the system, the selective spray system uses either a camera or a near-infrared sensor.
What The Tech Can Do
Selective spray systems can significantly reduce the amount of herbicide applied and reduce the costs of controlling weeds in certain crops. All selective spray systems generate a map during the spraying process, giving the grower a visual map of weed location and density. The visual weed map can be a valuable tool for your agronomist and in understanding what is happening in your field with weed pressure year over year. Selective spray can help in managing herbicide-resistant weeds by allowing the application of two different modes of action, particularly with a two-tank system.
Selective spray systems can locate a weed as small as 1/4".
What The Tech Can’t Do
There are limitations to green-on-green systems. They require a slower application speed of 9 mph to 12 mph to identify and spray the weed quickly when crossing the field. Like anything, the application speeds will increase given time and improved technology.
Selective green-on-green spray systems require distinguishable contrast between the weed and crop. Some weeds and crop are very similar in their leaf structure and growth characteristics. The best example is wild oats in a wheat crop; they look almost identical in the early growth stages when only experienced agronomists can identify the differences.
Using a green-on-green system requires access to a weed and crop identification library. John Deere confirmed at CES 2024 that the See & Spray Ultimate green-on-green system requires a $4 per acre fee for access to the corn libraries. The science behind the selective spray green-on-green system is the weed/crop image libraries all companies are generating, which teach the cameras to identify what they are seeing and to identify the weeds in the crop.
Selective spray systems only work with contact herbicides, which can kill the weed when applied to the weed leaves. Selective spray systems do not sense and precisely spray residual herbicides, which require broadcast application across an entire field and control weeds before
emergence. Systems with dual tank setup enable the application of a spot spray and a residual in one pass.
Spraying at night with selective spray green-on-green systems requires additional lights or different cameras. Some green-on-green systems can work at night, and
others cannot. The green-on-brown fallow system uses a different sensor to detect the green foliage in the field and can spray at night.
Future of Selective Spray
As selective spray technology matures, crops and weed image libraries will increase. Selective spray green on green is a new tool to help manage resistant weeds while reducing the amount of herbicides applied on a field.
Darryl Matthews, with more than three decades in the technology industry, brings his business sense and tech know-how to reveal opportunities for farmers.
