Detecting Canada Thistle in Spearmint with the Dual Camera System


Share | 11/02/2020

Canada Thistle
Canada Thistle. Photo by Jon Sailer on Unsplash

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Canada thistle, also known as creeping thistle, is an aggressive and noxious weed declared as a major agricultural pest. It threatens the productivity of croplands by competing for light, nutrients, and moisture with planted crops.

JSH Farms, an essential oil producer with farms along the Columbia River Basin of Washington and Oregon, has seen its peppermint and spearmint production threatened by infestations of this weed. The fact that both its peppermint and spearmint are perennial crops brings unique weed control challenges compared to annual crops.

To prevent major yield and quality losses, JSH Farms relies on Anderson Geographics LLC, a provider of GIS and remote sensing consultative services, to provide spot-spray prescription maps from weed classifications.

A Challenging Crop

In 2019 Anderson Geographics LLC used the MicaSense sensors RedEdge-MX and Altum to map several thousand acres of peppermint and provide spot-spray prescription maps for weed control. However, when following the same workflow on spearmint fields, the data captured resulted in too many false positives, even with precise training data captured via GPS throughout the field. The reason: the physiological characteristics of the spearmint.

Even though peppermint and spearmint are both species of mint, peppermint has higher levels of menthol (40%), a darker green coloration, and narrower leaves, while spearmint has lower menthol content (1%) and brighter-green spear-like leaves. The high variation of green across the spearmint field made it challenging to differentiate weeds from the planted crop.

A 10-band Solution

Looking to provide precise prescription maps for the spearmint field, Anderson Geographics LLC used the RedEdge-MX Dual Camera Imaging System, a 10-band solution that includes five bands in the red to red-edge region of the light spectrum for advanced species classification.

After flying the field with a DJI Matrice 100 equipped with the Dual Camera System and subsequently processing the data with Agisoft MetaShape, an accurate classification of thistle clumps was generated and provided to JSH farms where a total of 0.7 acres of thistle was detected in a  63.5-acre field.

Without the information provided by the Dual Camera System, the total spray area would have been 5.6 acres (7.7% more). The prescription map created from the Dual Camera imagery translated into $905-982 saved, as the cost of spraying with Stinger, a particularly aggressive herbicide, is $15.63 per acre. Furthermore, Anderson Geographics LLC only tested the Dual Camera System on half of a 125-acre field, thus a full field treatment would have equated to a product savings of $1,810-1,964 per field, per treatment, adding up to significant savings over time and across JSH’s extensive operations.

In addition to the potential cost savings, the employment of automated spot-spraying instead of broadcast treatment applications avoids unnecessary crop damage and increases product quality by lowering chemical signatures in the resulting mint oil.


The 10 bands on the Dual Camera System assisted detection and increased confidence in classification outputs. Furthermore, Anderson Geographics LLC determined that the additional bands included on the Dual Camera System could prove useful in future operations aimed at providing accurate prescription maps for managing Canadian thistle in spearmint.

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